Inaugurated in 1994 in Como, Italy, this series of conferences has become an important forum for scientists working on strong interactions, stimulating exchanges among theorists and experimentalists as well as across related fields.
The aim of the conference is to bring together people working on strong interactions from different approaches, ranging from lattice QCD to perturbative QCD, from models of the QCD vacuum to QCD phenomenology and experiments, from effective theories to physics beyond the Standard Model.
The scope of the conference also includes the interface between QCD, nuclear physics and astrophysics, and the wider landscape of strongly coupled physics. In particular, the conference will focus on the fruitful interactions and mutual benefits between QCD and the physics of condensed matter and strongly correlated systems.
The fifteenth edition of this conference series will take place at the University of Stavanger, Norway, August 1st - 6th, 2022.
I discuss how objects with topological charge 1/N can arise in CP(N-1) models in 1+1 dimensions, and in SU(N) gauge theories, without dynamical quarks, in 3+1 dimensions. The ansatz involves multivalued functions: a Z(N) vortex in the former, and a Z(N) monopole in the latter. Unlike classical instantons, such a quantum instanton has a fixed size on the order of the scale for confinement. They thus smoothly connect to the configurations found by Unsal, Poppitz et al. on a femto-slab. In gauge theories, as the object carries magnetic charge, they are confined by the presence of dynamical quarks. I discuss how they might affect the topological susceptibility in QCD at low temperatures and especially for cold, dense QCD.
In this talk I will discuss how mixed 0-form/1-form anomalies arise in the Hilbert space of gauge theories in 4d for arbitrary gauge group. I will show how the anomalies reveal an exact degeneracy of states for an arbitrary torus size. Finally, I will discuss some of the implications of our results for semiclassics, the infinite volume limit, and dualities.
The increasing accuracy in the experimental measurements of several hadronic observables related to weak processes, which in many cases is smaller than $\mathcal{O}(1\%)$, requires the inclusion in theoretical calculations of subleading corrections that were neglected so far. Over the past decade isospin breaking effects due to electromagnetic interactions and to the up-down quark mass splitting have been included by different collaborations in lattice QCD calculations of the hadron spectrum and of weak decays of mesons. In this talk we present the first RBC-UKQCD lattice calculation of the leading isospin-breaking corrections to the ratio of leptonic decay rates of kaons and pions into muon and neutrino, $\Gamma(K_{\ell 2})/\Gamma(\pi_{\ell 2})$. This computation is performed using domain wall fermions with close-to-physical (light and strange) quark masses. The QED effects are implemented using a perturbative approach and infrared divergences are regulated according to the QED$_\mathrm{L}$ prescription. We describe the strategy to extract the relevant hadronic matrix elements from Euclidean correlation functions and we discuss the important role of finite volume effects in this calculation.
I will present some recent state-of-the-art lattice QCD results revealing partonic structures of pion and kaon. These results will include valance parton distribution function of pion, pion distribution amplitude as well as electromagnetic form factor of kaon at large momentum transfers.
We have calculated the axial-vector form factors for the hyperon semileptonic decays $B_i \rightarrow B_f l \bar{\nu}$ in the chiral constituent quark model ($\chi$CQM). The decays considered here are the strangeness changing as well as strangeness conserving semileptonic decays of the hyperons. The conventional dipole form of parametrization has been used to analyse the $Q^2$ dependence of the axial-vector form factors ($g_i^{B_iB_f}(Q^2)$) as well their decay constants. The results have been compared with the experimental data and are found to be in good agreement with existing available data.
Most of the exotic quarkonium states have been observed in transitions to standard quarkonium states plus light-quark hadrons. However, so far very little is known of these transitions widths in the Born-Oppenheimer picture of exotic quarkonium, that is when exotic quarkonium are considered as heavy-quark-antiquark bound states over the spectrum of static energies for any given set of light degrees of freedom. In this talk we present the computation of the transitions for isospin I=0 exotic quarkonium to standard quarkonium with one or two light-quark mesons in the final state.The computation has two distinct parts: the heavy quark transition matrix elements, which are obtained in a nonrelativistic EFT incorporating the heavy quark, multipole and adiabatic expansions; and the hadronization of the gluonic operators into the light-meson final states. The single mesons production is obtained through the axial anomaly and a standard pi0-eta-eta' mixing scheme. Two pion and kaon production is obtained by solving the coupled Omnès problem.
In order to understand the nature of the XYZ particles, theoretical predictions of the various XYZ decay modes are essential. In this work, we focus on the decays of the heavy quarkonium hybrids in the EFT framework. We start with the weakly coupled potential NRQCD effective theory that describes systems with two heavy quarks and incorporates multipole expansions and use it to develop a Born-Oppenheimer effective theory (BOEFT) to describe the hybrids and compute the inclusive decay rates and semi-inclusive decay rates into traditional quarkonium. We find that our results of the decay rates are different from the previous theoretical studies and we also compare with the experimental data in PDG. We develop a systematic EFT framework in which the theoretical uncertainty can be systematically improved.
The diabatic approach in QCD [1-3] allows to describe a quarkoniumlike meson in terms of heavy quark-antiquark and open-flavor meson-meson pairs, interacting through a coupled-channel potential inferred from lattice calculations of string breaking [4]. In this talk, we present a systematic analysis of $J^{PC}=1^{++}$ charmoniumlike mesons with energies up to $4.0$ GeV within the diabatic framework. We show that the spectrum contains only two bound states: one conventional, assigned to the $1P$ charmonium state $\chi_{c1}(1P)$, and one unconventional, located very close below the $D^{0}\bar{D}^{\ast 0}$ threshold, which may be naturally identified with $\chi_{c1}(3872)$. The rest of the spectrum consists in a continuum of $D^{0}\bar{D}^{\ast 0}$ and $D^{+}D^{\ast -}$ scattering states, whose analysis indicates the presence of a resonance near $3960$ MeV, with a width of about $70$ MeV. We illustrate how this resonance, called $\chi_{c1}(2P)$ as it may be assigned to a mostly conventional $2P$ charmonium state, is likely overshadowed in its expected main decay channels, $D^{0}\bar{D}^{\ast 0}$ and $D^{+}D^{\ast -}$, by the threshold enhancements due to the loosely bound state, $\chi_{c1}(3872)$. Finally, we discuss alternative discovery channels.
[1] R. Bruschini, P.Gonzalez, Phys.Rev.D 102, 074002 (2020).
[2] R. Bruschini, P.Gonzalez, Phys.Rev.D 104, 074025 (2021).
[3] R. Bruschini, P.Gonzalez, Phys.Rev.D 105, 054028 (2022).
[4] G. S. Bali, H. Neff, T. Düssel, T. Lippert and K. Schilling (SESAM Collaboration), Phys. Rev. D 71, 114513 (2005).
The strongly intensive quantity $\Sigma$ is a new observable, introduced recently to the domain of heavy-ion physics. In superposition models which assume independent particle production from statistically identical sources, $\Sigma$ is insensitive to the number of sources and its fluctuations, contrary to the standard forward-backward correlation coefficient ($b_{\rm corr}$). Therefore, it provides direct information on the multiplicity correlations and fluctuations from a single source.
This talk presents new results on forward-backward correlations studied with the quantity $\Sigma$, measured by ALICE at the LHC in Xe--Xe reactions at $\sqrt{s_{\rm NN}}=5.44$~TeV and in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ and $5.02$ TeV.
The data are shown as a function of the gap between forward and backward pseudorapidity ($\eta$) intervals and the centrality of the collision. The study is made with two independent centrality estimators. An opposite trend of the values of $\Sigma$ as a function of centrality class in Pb--Pb and Xe--Xe collisions is observed for the experimental data and MC HIJING simulations. This nontrivial discrepancy implies that the physical mechanism of particle production differs from that predicted by the models.
NA61/SHINE is an experiment at the CERN Super Proton Synchrotron. The main goals of the experiment are the search for the critical point of strongly interacting matter and study the properties of the onset of deconfinement. In order to reach these goals, the two-dimensional scan in beam momentum (13A-150A GeV/c) and system size (p+p, Be+Be, Ar+Sc, Xe+La, Pb+Pb) was performed.
In the final stage of the collision, when resonance decays and re-scattering are important, the spectra of protons are not as affected as of pions, due to the large difference in mass. Thus, proton rapidity distribution is especially sensitive to the onset of deconfinement.
This contribution presents experimental results on proton production relevant for the onset of deconfinement. Experimental techniques and methods used to analyse hadrons will be reviewed. Examples of transverse momentum and rapidity spectra will be also shown. Moreover, a comparison with the existing data will be given.
We present the most recent results from the FASTSUM collaboration for hadron properties at high temperature from anisotropic lattice QCD. This includes the temperature dependence of the light and charmed meson and baryon spectrum, as well as properties of heavy quarkonia. We also present the status of our next generation gauge ensembles.
Determining the phase structure of Quantum Chromodynamics (QCD) and its Equation of State (EoS) at densities and temperatures realised inside neutron stars and their mergers is a long-standing open problem.
I will present a framework for the EoS of dense and hot QCD that describes the deconfinement phase transition between a dense baryonic and quark matter phase via the holographic V-QCD model.
This model is then used in fully general relativistic hydrodynamic simulations of binary systems that are consistent with the first ever observed neutron star merger event GW170817 and the consequences on the formation of quark matter and the emitted gravitational wave signal are studied.
This presentation is based on 2112.12157 and 2205.05691.
Description of nuclear matter in the core of neutron stars eludes the main tools of investigation of QCD, such as perturbation theory and the lattice formulation of the theory. Recently, the application of the holographic paradigm (both via top-down and bottom-up models) to this task has led to many encouraging results, both qualitatively and quantitatively. In this talk, I will present our approach to the description of neutron star cores, relying on a simple model of the (double) hard-wall type: I will discuss results concerning the nature of homogeneous nuclear matter at high density emerging from the model including a quarkyonic phase, the mass-radius relation for neutron stars, as well as the rather stiff equation of state we have found.
I will show how, despite the very simple model employed, for an appropriate calibration we were able to obtain neutron stars that only slightly fall short of the observational bounds on radius and tidal deformability. Finally, I will show results from simulations of mergers of neutron star pairs, including the characteristic gravitational waves signal and its frequency spectrum.
I will discuss the recent description of realistic neutron stars using a model derived from holography in [2111.03374,2112.10633]. After a brief review of beta-equilibrated isospin-asymmetric dense holographic baryonic matter within the Sakai-Sugimoto model, I will discuss how the resulting equation of state is used for constructing the full compact star within a single framework with only two free parameters. This includes both the core and (a simplified version of) the crust, so that the location of the crust-core transition can be computed fully dynamically. Within a physically reasonable window of the parameters space, the resulting stars have radii, masses and tidal deformabilities that satisfy all known astrophysical constraints. Moreover, by combining our theoretical results with the latest astrophysical data, we are able to derive more stringent constraints than given by the data alone. For instance, our calculation predicts -- independent of the model parameters -- an upper limit for the maximal mass of the star of about 2.46 solar masses and a lower limit of the (dimensionless) tidal deformability of a 1.4-solar-mass star of about 277.
This study explores the utility of a kernel in complex Langevin simulations of quantum real-time dynamics on the Schwinger-Keldysh contour. We give several examples where we use a systematic scheme to find kernels that restore correct convergence of complex Langevin. The schemes combine prior information we know about the system and the correctness of convergence of complex Langevin to construct a kernel. This allows us to simulate up to $2\beta$ on the real-time Schwinger-Keldysh contour with the $0+1$ dimensional anharmonic oscillator using $m=1, \; \lambda=24$, which was previously unattainable using the complex Langevin equation.
Gauge/gravity duality is a great vehicle to guide one's path when strongly coupled. We show that this duality will explain many unusual scaling laws for bipartite entanglement entropy and quark-anti-quark potentials present in the numerical data we obtain from the lattice Yang-Mills theory in three- and four dimensions. We also discuss their dual gravity descriptions.
Finding order parameters for the detection of critical phenomena and self-similar behavior in and out of equilibrium is a challenging endeavour in non-Abelian gauge theories. Tailored to detect topological structures in noisy data and accompanied by stability and limit theorems, persistent homology allows for the construction of sensible and sensitive observables. Based on state-of-the-art hybrid Monte Carlo simulations of SU(2) lattice gauge theory I will show how the persistent homology of filtrations by chromoelectric and -magnetic fields, topological densities and Polyakov loops can be used to gauge-invariantly and without cooling algorithms uncover interpretable features of the confinement-deconfinement phase transition. In classical-statistical simulations far from equilibrium persistent homology observables reveal clear self-similar scaling related to a nonthermal fixed point, demonstrating the universality of scaling beyond correlation functions. Our results showcase the extensive versatility of persistent homology in non-Abelian gauge theories.
Recently, the introduction of relevant physical information into neural network architectures has become a widely used and successful strategy for improving the network's performances. In lattice field theories, such information can be identified with gauge symmetries, which are incorporated into the network layers of our recently proposed Lattice Gauge Equivariant Convolutional Neural Networks (L-CNNs) [1]. Previously, we showed how L-CNNs can generalize better to differently sized lattices than traditional neural networks and that they are robust against adversarial gauge transformations.
In this talk, we present our progress on possible applications of L-CNNs as a tool to modify gauge field configurations such as Wilson flow or normalizing flows.
Our methods are based on ordinary differential equations (ODE) parametrized by neural networks (neural ODEs) which allow us to modify link configurations in a gauge equivariant manner.
For simplicity, we focus on simple toy models to test these ideas in practice.
[1] M. Favoni, A. Ipp, D. I. Müller, D. Schuh, Phys.Rev.Lett. 128 (2022) 3, 3 [arXiv:2012.12901]
After examining the mass and pressure decompositions of hadrons in the stress-energy-momentum tensor, it is found that the glue part of the trace anomaly can be identified as originated from the vacuum energy of the glue condensate and gives a CONSTANT restoring pressure which balances that from the traceless part of the Hamiltonian (quark and glue kinetic energies) to confine the hadron, much like the cosmological constant Einstein introduced for a static universe. From a lattice calculation of this anomaly in the charmonium, we deduce the associated string tension which turns out to be in good agreement with that from a Cornell potential calculation which fits the charmonium spectrum.
One notices that the analogy extends to type II superconductors where the potential for the magnetic field in the Ginzburg-Laudau equation is the number of Cooper pairs times the energy gap of each pair. This gives a negative pressure to balance the pressure from the magnetic energy in the normal phase. Thus, all three confinement mechanisms mentioned above are related to the presence of a condensate.
A misery of why the pion mass approaches zero at the chiral limit is solved. The pion mass can be expressed by the sigma term and the trace anomaly. While the sigma term vanishes as \sqrt{m_q}, the trace anomaly has no quark mass dependence. Why does it approach zero at the chiral limit? A lattice calculation of the trace anomaly reveals that it changes sign in its spatial distribution as the quark mass decreases which is like the ring-shaped type II superconductor. This is perhaps the only example that the structure of the conformal symmetry breaking is dictated by the chiral symmetry breaking.
In this talk I will give an overview on recent results on the spectrum and properties of
conventional mesons and exotic mesons (glueballs and four-quark states) as obtained in
the framework of Dyson-Schwinger and Bethe-Salpeter equations with particular focus on
states with the quantum numbers of a scalar.
I will discuss the spectrum of (quenched) glueballs and compare with results from lattice
gauge theory. For four-quark systems I will summarize results for light quarks and discuss
mixing effects with conventional meson states. I will also highlight recent progress on
discriminating between four-quark, molecule or hadro-quarkonium configurations in heavy-light
systems.
Confinement of 4d gauge theories is usually the strong-coupling problem, and it is a difficult task to understand even its qualitative features. We are trying to develop its semiclassical understanding based on the idea of volume independence or adiabatic continuity. We conjecture that the strong-coupling regime of many 4d gauge theories is continuously connected to the weak-coupling theories on small $\mathbb{R}^2\times T^2$ with the nontrivial 't Hooft flux. We explicitly confirm the fractional theta periodicity for pure YM and chiral Lagrangian for QCD can be derived in this small $T^2$ regime, which partly justifies our conjecture. We also uncover why this is possible in view of anomaly-preservation of this compactification.
The last two decades have witnessed the discovery of a myriad of new and
unexpected hadrons. The future holds more surprises for us, thanks to
new-generation experiments. Understanding the signals and determining
the properties of the states requires a parallel theoretical effort. To
make full use of available and forthcoming data, a careful amplitude
modeling is required, together with a sound treatment of the statistical
uncertainties, and a systematic survey of the model dependencies. In th
talk, I will highlight several exciting studies made by the Joint
Physics Analysis Center in the field of spectroscopy of light hadrons.
The flow of information in high-energy collisions has been recently investigated by various groups. Entanglement entropy of the proton becoming classical information entropy of pdfs, jet splitting affecting entropy, or the entropy in hadron decays have already been reported in the literature. Here we examine aspects of fragmentation functions in this context, including their entropy as probability distributions and the relation of Barone, Drago and Ma between FFs and pdfs.
We investigated the two scalar glueball
scattering and the possible emergence of a bound state,
that we call glueballonium. The scalar glueball, the lightest particle of the
YM sector of QCD, has a lattice predicted mass of about
$m_{G}\simeq1.7$ GeV. We performed this study in the context of a
widely used dilaton potential, that depends on a single dimensionful parameter $\Lambda_G$. The unitarization considered by us allowed us to predict the lowest partial waves in the elastic window. Furthermore, we
also show that a glueballonium forms if $\Lambda_{G}$ is small enough. In particular, for
$\Lambda_{G}$ compatible with the expectations from the gluon condensate, the glueballonium has a mass of about $3.4$ GeV.
The Belle experiment at the KEKB energy-asymmetric e+-e- collider
accumulated dataset with integrated luminosity of 1/ab, including
Upsilon(nS) on resonances, off-resonances, and Upsilon(5S) scan data. And
the Belle II experiment is a substantial upgrade of the B factory facility,
with much higher instantaneous luminosity and will accumulate 50/ab of
data. Belle II has already accumulated about 400/fb of dataset, as well as
the Y(10750) scan data at four energy points with the luminosity of
19.22/fb. With these datasets, Belle and Belle II would be able to search
for new states on charmonium, bottomonium, and baryons spectroscopies, and
measure their properties. In this presentation, we will review the latest
spectroscopy results from Belle and Belle II.
We report our analysis for the static energy in (2+1+1)-flavor QCD over a wide range of lattice spacings and several quark masses, including the physical quark mass with ensembles of lattice-gauge-field configurations made available by the MILC Collaboration. We obtain results for the static energy out to distances of nearly 1fm, allowing us to perform a simultaneous determination of the lattice scales r1 and r0 as well as the string tension, σ. For the smallest three lattice spacings we also determine the scale r2. While our results for r0/r1 and r0 √σ agree with published (2+1)-flavor results, our result for r1/r2 differs significantly from the value obtained in the (2+1)-flavor case, which is most likely due to the effect of the charm quark. We study in detail the effect of the charm quark on the static energy by comparing our results on the finest two lattices with the previously published (2+1)-flavor QCD results at similar lattice spacing. We find that for r > 0.2fm our results on the static energy agree with the (2+1)-flavor result, implying the decoupling of the charm quark for these distances. For smaller distances, on the other hand, we find that the effect of the dynamical charm quark is noticeable. The lattice results agree well with the two-loop perturbative expression of the static energy incorporating finite charm mass effects. The perturbative expression features decoupling at large distances, an effective running with four massless quarks at very short distances, and finite charm mass effects at distances comparable with the inverse of the charm mass. This is the first time that the decoupling of the charm quark is observed and quantitatively analyzed on lattice data of the static energy.
The existence of the X(3872) resonance extremely close to the D∗0 D0-bar threshold implies that neutral charm mesons have an approximate nonrelativistic conformal symmetry. Systems consisting of these mesons with small kinetic energies produced in a short-distance reaction are unparticles that can be created by an operator with definite scaling dimensions in a nonrelativistic conformal field theory. There is a scaling region in which their energy distribution has power-law behavior with an exponent determined by the scaling dimension of the operator. The unparticle associated with two neutral charm mesons produces a peak in the recoil momentum spectrum of K± in inclusive decays of B±. The scaling dimensions of the unparticles associated with three neutral charm mesons are calculated. They can be determined experimentally by measuring the invariant mass distribution for X D0 in prompt production at the Large Hadron Collider.
One of the primary goals of heavy-ion physics is to understand the transport properties of the quark-gluon-plasma (QGP) which comprises the tiniest constituents, quarks and gluons, that prevailed in the first few microseconds after the Big Bang.
The present most challenging part of the research is pinning down the critical point of the QGP, where the shear viscosity over entropy ratio ($\eta/s$) is at its minimum and very close to the lowest value in nature $1/(4\pi)$. Significant advances based on flow harmonic analysis have been made up to date. However, there are still few remaining challenges in experiments and theory to constrain the temperature dependence of $\eta/s$ and $\zeta/s$ of the QGP. In this talk, I will highlight the latest results from LHC experiments in this regard and discuss aforementioned challenges.
Collective phenomena have proved to be crucial probes to the transport properties of the quark-gluon plasma (QGP) created in ultrarelativistic heavy-ion collisions. One manifestation of these effects is the anisotropic azimuthal distribution of the particles produced in such collisions, which can be parametrized with two distinct degrees of freedom: the flow amplitudes v_n and the symmetry planes 𝛹_n. The measurements of the correlations between two different flow amplitudes, using the Symmetric Cumulants (SC), have shown the importance of investigating the intercorrelations among different flow amplitudes v_n and v_m, as they present more sensitivities in constraining the QGP properties.
In this talk, we highlight the advancements made in the measurements of the correlated fluctuations between multiple flow harmonics. We demonstrate how the well-known SC observables have been generalised to more than two harmonics and to different moments of those, using the cumulant formalism. We also show a newly developed estimator for correlations between 𝛹_n for the first time without the influence of correlations between v_n.
The existence and location of the QCD critical point is an object of both experimental and theoretical studies. The comprehensive data collected by the NA61/SHINE during a two-dimensional scan in beam momentum (13A-150A GeV/c) and system size (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb) allows for a systematic search for the critical point – a search for a non-monotonic dependence of various correlation and fluctuation observables on collision energy and size of colliding nuclei. In particular, fluctuations of particle number in transverse momentum space are studied. They are quantified by measuring the scaling behavior of factorial moments of multiplicity distributions.
This contribution reviews ongoing NA61/SHINE studies to search for the critical point of the strongly interacting matter.
NLO evolution of the Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner (JIMWLK) equation with massless quarks was derived a few years ago. We make a step further to compute the evolution kernels focusing on the effects due to finite quark masses. To this goal, the light-cone wave function of a fast moving dilute hadronic projectile is computed up to ${\cal O}(g^3)$ in QCD coupling constant. Compared with the massless case, a new IR divergence emerges, which is eventually canceled by a mass dependent counter term. Our results extend the theoretical tools used in physics of gluon saturation and aim at improving precision in future phenomenological applications.
We present predictions for the second- and fourth-order curvature coefficients of the QCD phase transition line using the NNLO HTLpt-resummed thermodynamic potential. We present three cases corresponding to (i) $\mu_s = \mu_l = \mu_B/3$, (ii) $\mu_s=0$, $\mu_l = \mu_B/3,$ and (iii) $S = 0$, $Q/B = 0.4$, $\mu_l = \mu_B/3$. In all three cases, we find excellent agreement with continuum extrapolated lattice QCD results for $\kappa_2$, given current statistical uncertainties. We also make HTLpt predictions for $\kappa_4$ in all three cases, finding again excellent agreement with lattice extractions of this coefficient where available.
A well known technique to determine the decay amplitudes of non-leptonic B meson processes is QCD factorization. One of the main issues faced by this procedure is the analytical determination of power suppressed terms, for instance of annihilation topologies. In this talk we describe the extraction of the annihilation contributions from data. Our method is based on establishing a set of rules which allow to transform the SU(3)-invariant description of B decay amplitudes into pairs of psudoscalar particles and the QCD factorization decomposition. Our approach provides not only the size of this contributions from phenomenological considerations but also a formal proof of the maximal number of degrees of freedom in the SU(3)-invariant, the topological and the QCD-factorization representations of B decay amplitudes into Pseudoscalar particles.
Cold and dense matter can be explored in a systematic way both in the high-density (perturbative QCD) and low-density (Chiral EFT) regime. However, the path connecting them is yet to be discovered. As a result, these descriptions are usually extrapolated into the intermediate density regime and then connected at some transition point. In this work I will present a model that has features of both, but within a unified description. The model contains hadronic degrees of freedom and is calibrated using nuclear matter properties; yet it exhibits a phase transition towards a “quark matter” phase that has approximately restored chiral symmetry, strangeness, and asymptotes to the conformal limit of the speed of sound. While this model can describe different qualitative scenarios regarding the phase transition and the strangeness onset, empirical constraints significantly narrow down the allowed parameter range. Moreover, hybrid stars above two solar masses are predicted, exhibiting a stiff “quark matter” core. This approach has implications for the hyperon puzzle and is also crucial for future exploration of inhomogeneous phases and the surface tension between hadron and quark phases.
Lattice methods are spectacularly successful in measuring thermodynamic properties of strongly interacting matter described by Quantum Chromodynamics (QCD) at small baryon densities, however the existing lattice techniques cannot be easily extended to large densities due to the infamous "sign problem". In this work we have studied the hadronic phase of QCD using relativistic nuclear mean field models for a large range of baryon densities. We have specifically chosen two hadronic models which are well constrained from the neutron star merger data. We have compared different thermodynamic observables like the fluctuations of baryon number, electric charge, strangeness, etc calculated within these models at $\mu_Q/\mu_B=0.4$ and zero net strangeness to the exact results available from lattice QCD. This may allow one to better constrain such models, and in understanding the relative importance of different hadronic interactions. We have also estimated the line of constant energy density, as obtained from lattice QCD near the crossover region at $\mu_B=0$, for a wide range of net-baryon densities. Furthermore choosing the two models, one with and other without strangeness, allows us to understand the relative importance of the latter near the chiral pseudo-critical region for a wide range of $\mu_B$.
The possible existence of hybrid stars is studied using several multi-quark interaction channels. The hadronic phase consists of an EOS with presently accepted nuclear matter properties and the quark model constrained by the vacuum properties of several light mesons. The dependence of several NS properties on the different quark interactions is analyzed. We show that the present constraints from neutron stars observations allow for the existence of hybrid stars with a large strangeness content and large quark cores.
In the context of warped five-dimensional models formulated to understand the physics beyond the Standard Model (SM), we will discuss the prediction of a continuum of Kaluza-Klein modes on top of the SM zero modes, with a mass gap. We compute the Green’s functions for gauge bosons and describe how the continuum is reached from a discretized theory. We also study the Green's functions for the graviton and the radion, as well as the couplings of these fields with SM matter fields. This work is based on Refs. [1-3]. Other related references are [4-8].
[1] E. Megias, M. Perez-Victoria, M. Quiros, "Spectral properties of warped models", in preparation (2022).
[2] E. Megias, M. Quiros, “Analytical Green's functions for continuum spectra”, JHEP 09 (2021) 157. arXiv:2106.09598[hep-ph].
[3] E. Megias, M. Quiros, “Gapped continuum Kaluza-Klein spectrum”, JHEP 08 (2019) 166. arXiv:1905.07634 [hep-ph].
[4] L. Randall, R. Sundrum, “A Large mass hierarchy from a small extra dimension”, PRL 83 (1999) 3370-3373.
[5] C. Csaki et al., “Continuum Naturalness”, JHEP 1903 (2019) 142.
[6] C. Csaki et al., “Continuum Dark Matter”, arXiv:2105.07035 [hep-ph].
[7] G. Giudice et al, “Clockwork/Linear Dilaton: Structure and Phenomenology”, JHEP 1806 (2018) 009.
[8] L. Randall and G. Servant, “Gravitational waves from warped space”, JHEP 0705 (2007), 054.
We analyze [1] the next to leading order (NLO) graviton-graviton scattering amplitude via the Inverse Amplitude Method (IAM), well known to low-energy QCD practitioners [2]. Like the electroweak chiral lagrangian, successfully used for low-energy QCD, the Einstein-Hilbert (EH) lagrangian is a non-linear and non-renormalizable theory whose most relevant operator is a dimension two one containing two derivatives of the dynamical lagrangian. Both lagrangians contain a dimensionful constant in four dimensions: $f_\pi$ for the pion lagrangian and the Planck mass $M_P$ for the EH lagrangian. However, the EH lagrangian describing gravity is a gauge theory.
We use the tree-level graviton-graviton scattering amplitude given in [3] and the NLO computation done by Dunbar and Norridge [4] using string theory methods. Only counterterms proportional to $\mathcal{R}^2$, $\mathcal{R}_{\mu\nu}\mathcal{R}^{\mu\nu}$ and $\mathcal{R}_{\alpha\beta}^{\gamma\delta}\mathcal{R}_{\gamma\delta}^{\alpha\beta}$ are needed [3]. On-shell (lowest order equations of motion) these counterterms vanish, so that the theory is UV finita at NLO.
Dispersion relation via the inverse amplitude method [2,5] are used to seek for hypothetical graviton-induced resonances similar to those appearing in QCD. We focus on the $++++$ and $----$ helicity channels and analyze the $J=0$, $2$ and $4$ partial waves. We look for resonances on the second Riemann sheet as well as for artifacts in the first Riemann sheet. The study of these artifacts is necessary since their appearance can mean that the inverse amplitude method is being applied beyond its validity conditions.
[1] R.L.Delgado, A.Dobado, D.Espriu, to appear on arXiv
[2] A.Dobado, J.R.Pelaez, Phys.Rev.D{\bf 56} (1997) 3057-3073
[3] G.'t Hooft, M.Veltman, Ann.Inst.H.Poincaré A{\bf 20} (1974), 69
[4] D.C.Dunbar, P.S.Norridge, Nucl.Phys.B{\bf 433} (1995), 181-208
[5] Rafael L.Delgado, A.Dobado, F.J.Llanes-Estrada, Phys.Rev.D{\bf 91} (2015) 7, 075017
Strongly-coupled dark sectors offer natural UV-complete extensions to the Standard Model that are challenging to access experimentally if they are only weakly coupled to the Standard Model. In this talk, I will present the possibility to test these dark sectors via gravitational-wave signals from the dark confinement phase transition. Due to the non-perturbative nature of the QCD-like sectors, we adapt Lattice data to effective Polyakov-loop models from which we can compute the bubble nucleation in the early Universe and eventually the statistical gravitational-wave signal. I will present results for general SU(N) Yang-Mills sectors allowing a birds-eye view on the dependence on the number of dark colours.
The talk is based on: "Testing the dark SU(N) Yang-Mills theory confined landscape: From the lattice to gravitational waves" (https://arxiv.org/abs/2012.11614)
The identification of universal properties from minimally processed data sets is one goal of machine learning techniques applied to statistical physics. Here, we study how the minimum number of variables needed to accurately describe the important features of a data set - the intrinsic dimension (Id) - behaves in the vicinity of phase transitions. We employ state-of-the-art nearest neighbors-based Id-estimators to compute the Id of raw Monte Carlo thermal configurations across different phase transitions: first-, second-order and Berezinskii-Kosterlitz-Thouless. For all the considered cases, we find that the Id uniquely characterizes the transition regime. The finite-size analysis of the Id allows not just to identify critical points with an accuracy comparable with methods that rely on a priori identification of order parameters, but also to determine the corresponding (critical) exponent in case of continuous transitions. Our work reveals how raw data sets display unique signatures of universal behavior in the absence of any dimensional reduction scheme, and suggest direct parallelism between conventional order parameters in real space, and the intrinsic dimension in the data space.
The design of optimal test statistics is a key task in frequentist statistics and for a number of scenarios optimal test statistics such as the profile-likelihood ratio are known. By turning this argument around we can find the profile likelihood ratio even in likelihood-free cases, where only samples from a simulator are available, by optimizing a test statistic within those scenarios. We propose a likelihood-free training algorithm that produces test statistics that are equivalent to the profile likelihood ratios in cases where the latter is known to be optimal.
We consider the massless charge-N Schwinger model and its deformation with two four-fermion operators. Without the deformations, this model exhibits chiral symmetry breaking without confinement. It is usually asserted that the massless Schwinger model is always deconfined and a string tension emerges only when a mass for the fermion field is turned on. We show that in the presence of these four-fermion operators, the massless theory can in fact confine. One of the four-fermion deformations is chirally neutral, and is a marginal deformation. The other operator can be relevant or irrelevant, and respects a ℤ_2 subgroup of chiral symmetry for even N, hence forbidding a mass term. When it is relevant, even the exactly massless theory exhibits both confinement and spontaneous chiral symmetry breaking. The construction is analogous to QCD(adj) in 2d. While the theory without four-fermion deformations is deconfined, the theory with these deformations is generically in a confining phase. We study the model on ℝ_2 using bosonization, and also analyze the mechanism of confinement on ℝ×S1, where we find that confinement is driven by fractional instantons.
Ample numerical evidence from lattice calculations shows a strong connection between the confining properties of gauge theories at finite temperature and the localisation properties of the low-lying Dirac eigenmodes. In this talk I review recent progress on this topic, including results for QCD at imaginary chemical potential ${\mu}_I/T = \pi$ at temperatures above the Roberge-Weiss transition temperature. These confirm the general picture of low modes turning from delocalised to localised at the deconfinement transition, in a previously unexplored setup with a genuine, physical transition in the presence of dynamical fermions. This further supports the use of Dirac eigenmodes as a tool to investigate the mechanisms behind confinement and the deconfinement transition.
Using the approach based on conformal symmetry we calculate the two-loop coefficient function for the axial-vector contributions to two-photon processes in the MS¯ scheme. This is the last missing element for the complete next-to-next-to-leading order (NNLO) calculation of the pion transition form factor γ*γ→π in perturbative QCD. The corresponding high-statistics measurement is planned by the Belle II collaboration and will allow one to put strong constraints on the pion light-cone distribution amplitude. The calculated NNLO corrections prove to be rather large and have to be taken into account. The same coefficient function determines the contribution of the axial-vector generalized parton distributions to deeply virtual Compton scattering (DVCS) which is investigated at the JLAB 12 GeV accelerator, by COMPASS at CERN, and in the future will be studied at the Electron Ion Collider EIC.
Recent years have brought a breakthrough for calculations of partonic distributions on a Euclidean lattice. In this talk, I will discuss our progress in extracting generalized parton distributions (GPDs) from the quasi-distribution approach. I will present both the leading-twist GPDs and our exploratory studies of selected twist-3 cases.
We perform lattice QCD simulations in order to calculate nucleon four-point functions, which can be used to extract Mellin moments of double parton distributions (DPDs). In this first study, we consider the first DPD Mellin moment of the unpolarized proton. We employ an $n_f = 2+1$ ensemble with pseudoscalar masses of $m_\pi = 355~\mathrm{MeV}$ and $m_K = 441~\mathrm{MeV}$, the results are converted to the $\overline{\mathrm{MS}}$-scheme at the scale $\mu = 2~\mathrm{GeV}$. Our calculation includes all Wick contractions, where for almost all of them a good statistical signal is obtained. We analyze the dependence on the quark flavor and the quark polarization. Furthermore, the validity of frequently used factorization assumptions is investigated.
In recent years, the BESII and BESIII collaborations have provided a lot of new and accurate data on baryon decays of S-wave charmonium states.
These data indicate about sizable effects associated with power corrections to the well known leading-order approximation.
In my talk I will discuss a description of $J/psi\to B\bar B$ decays within the effective field theory framework (NRQCD & QCD collinear factorisation) and discuss the role of power corrections provided by the valence higher twist operators, which appear in the light-cone expansion of baryon wave functions.
The peak region in heavy quark production is best described in boosted heavy quark effective theory, where its mass is integrated out. Within this approach the cross section can be factorized into hard, jet and soft func- tions, and large logs associated with the mass can be summed up to all orders.
In this talk we present the computation of the missing pieces to get the bHQET thrust and heavy-jet-mass distributions with non-vanishing secondary quark masses at NNLO: the jet and hard functions. The differ- ence with respect to the massless case is encoded in the massive bubble diagrams. For its computation we use a dispersive integral method that permits expressing the result as an analytic, fast-converging expansion in powers of a small parameter rather than integrals that can only be solved numerically.
We also obtained the matching coefficient that shows up when integrat- ing out the secondary quark mass as well. It is necessary for a continuous top-down running and to verify a very important consistency check.
Heavy quarkonium production of high transverse momentum ($p_T$) in hadronic collisions can be pursued in the QCD factorization formalism with heavy quarkonium fragmentation functions (FFs). The scale evolution of quarkonium FFs enables us to resum logarithmically enhanced corrections $\alpha_s\ln(p_T^2/m^2)$ with heavy quark mass $m$, which is an essential piece to explore the nonperturbative process of bound quarkonium formation. Boundary conditions of the evolution equations of the FFs at $p_T\sim 2m$ are given by combining perturbatively calculable coefficients in NRQCD and long-distance-matrix elements (LDMEs) for different intermediate states of a produced heavy quark pair. LDMEs correspond to relative weights of individual terms after expanding the input FFs in quark velocity $v$, and should be determined by data fitting.
We demonstrated in Ref.[1] that the QCD factorization approach at leading-power in $1/p_T$ with single parton FFs at twist-2 describes LHC data on the differential cross-section for $J/\psi$ production in hadronic collisions at $p_T$ much larger than the heavy quark mass scale. Meanwhile, at $p_T= \mathcal{O}(2m)$, the subleading power contribution with double parton FFs at twist-4 is more significant than the leading power contribution. In this talk, we will emphasize the role of the subleading power corrections in hadronic quarkonium production. Our recent analysis of the scale evolution of the twist-4 double parton FFs will be shown [2], and the application of the QCD factorization approach to other quarkonium production processes will be discussed.
[1] K.Lee, J.-W.Qiu, G.Sterman, and K.Watanabe, [arXiv:2108.00305 [hep-ph]].
[2] K.Lee, J.-W.Qiu, G.Sterman, and K.Watanabe, in preparation.
One of the key challenges of hadron physics today is understanding the origin of strangeness enhancement in high-energy hadronic collisions, i.e. the increase of (multi-)strange hadron yields relative to non-strange hadron yields with increasing charged-particle multiplicity. What remains unclear is the relative contribution to this phenomenon from hard and soft QCD processes and the role of initial-state effects such as effective energy. The latter is the difference between the total centre-of-mass energy and the energy of leading baryons emitted at forward/backward rapidities. The superior tracking and particle-identification capabilities of ALICE make this detector unique in measuring (multi-)strange hadrons via the reconstruction of their weak decays over a wide momentum range. The effective energy is measured using zero-degree hadronic calorimeters~(ZDC).
In this talk, recent results on $\mathrm{K^0_S}$ and $\Xi^\pm$ production in- and out-of-jets in pp collisions at $\sqrt{s}=13$ TeV using the two-particle correlation method are presented. To address the role of initial and final state effects, a double differential measurement of (multi-)strange hadron production as a function of multiplicity and effective energy is also presented.
The present results suggest that out-of-jet processes give the dominant contribution to strange particle production and provide new insights on the role of initial state effects in strangeness enhancement in pp collisions.
We develop a new approach to the initial state of heavy-ion collisions by extending the weak field approximation of the Color Glass Condensate formalism beyond the boost invariant limit [1]. Our analytical calculation yields surprisingly simple results for the color fields and the field strength tensor of the Glasma produced in the collision. As an explicit check, we demonstrate quantitative agreement with non-perturbative 3+1D lattice simulations in the weak field limit. We further investigate how longitudinal color charge correlations within the nuclei determine the rapidity profile of the transverse pressure of the Glasma and discuss ideas for new 3+1D initial state models using our framework.
[1] A. Ipp, D. Müller, S. Schlichting and P. Singh, Phys.Rev.D 104 (2021) 11, 114040 [arXiv:2109.05028]
The recently observed 4.2-$\sigma$ tension between experimental measurement and theoretical prediction of the muon magnetic moment highlights the need for improved control of uncertainties. On the theoretical side, one of the contributions of interest is the hadronic light-by-light (HLbL). In the dispersive data-driven evaluation of the HLbL, certain short-distance constraints obtained by means of operator product expansion techniques play a central role, as explained thoroughly in the white paper [2006.04822]. In this talk, we will present previous work [1908.03331,2008.13487,2101.09169] and on-going efforts on such constraints for different kinematical regions occurring in the HLbL loop-integrations, and their impact on the muon g-2.
The discrepancy between the fixed-order (FOPT) and contour-improved (CIPT) expansions for tau hadronic spectral function moments has been a subject of intense investigations for more than a decade and constituted a major theoretical uncertainty for strong coupling determinations from hadronic tau decay spectral data. Recently, it has been shown by some of us that a discrepancy between the FOPT and CIPT expansions arises in the presence of IR renormalons in the underlying Adler function perturbation series, and that the CIPT expansion is inconsistent with the standard form of the OPE corrections. The observed CIPT-FOPT discrepancy at the 5-loop level may be due to this property. The discrepancy that is caused by the IR renomalon associated to the gluon condensate OPE correction plays the most important numerical role. We show that the FOPT and CIPT expansions can be reconciled by adopting a renormalon-free scheme for the gluon condensate that is in close analogy to scheme changes from the pole quark mass to short-distance heavy quark masses. This removes the discrepancy between the FOPT and CIPT expansions, improves their convergence and may lead to more precise determinations of the strong coupling. In the talk we review the conceptual background of the original FOPT-CIPT discrepancy related IR renormalons and show how the discrepancy is removed exactly in large-order renormalon models. We demonstrate how well the scheme can be applied in practical phenomenological analyses based on the known loop corrections, where the strength of the gluon condensate renormalon is only known approximately and uncertainties related to scheme-variations for the renormalon-free gluon condensate must be accounted for.
The LHCb Collaboration has recently discovered a structure around 6.9 GeV in the double-$J/\psi$ mass distribution, possibly a first fully-charmed tetraquark state $X(6900)$. Based on vector-meson dominance (VMD) such a state should have a significant branching ratio of decaying into two photons ($\gamma \gamma$). We show that the published ATLAS data for the light-by-light scattering may indeed accommodate for such a state, with $\gamma \gamma$ branching ratio of order of $10^{-4}$, which is larger even than the value inferred by the VMD. The spin-parity assignment $0^{-+}$ is in better agreement with the VMD prediction than $0^{++}$, albeit not significantly at the current precision. Further light-by-light scattering data in this region, clarifying the nature of this state, should be obtained in the Run 3, and probably in the high-luminosity phase of the LHC (Run 4 etc.).
In this talk, I will discuss the phase diagram at finite isospin density using
two and three flavor chiral perturbation theory. I will also discuss the quark and pion condensates in the pion-condensed phase at T=0. Moreover, the pion-condensed phase has many interesting properties. At small chemical potentials, the system behaves as a dilute nonrelativistic Bose gas with an effective s-wave scattering length given by
chiral perturbation theory. In the chiral limit, the Goldstone boson has an exact
linear dispersion relation. Using effective field theory methods, one can construct
a low energy theory for this massless modes. The couplings in this Lagrangian can be determined order by order using matching. The massless mode moves with a speed
slower than the speed of light due to the medium and renormalization effects
involving the s-quark.
Chiral perturbation theory in the presence of the chiral anomaly predicts a so-called chiral soliton lattice in the presence of a magnetic field and a baryon chemical potential. This phase becomes unstable with respect to charged pion condensation if the magnetic field is further increased. I will point out that this instability bears a striking resemblance to the well-known instability at the second critical magnetic field of a type-II superconductor. This analogy is exploited to analytically construct an inhomogeneous superconducting phase of charged pions in coexistence with a supercurrent of neutral pions. The resulting phase is energetically favored over the chiral soliton lattice and exhibits spatially oscillating topological baryon number in the plane perpendicular to the magnetic field.
[Reality of the Crosssover Scenarios]
Because the ab-initio EOSs from the $\chi$EFT and the pQCD are both soft, it is unlikely to have a 1st-order phase transition to quark matter that would make the EOS even softer. These calculations as well as observational data and discussions of quark-hadron continuity / quarkyonic matter support the scenario of smooth and continuous realization of quark matter. I will make a quick overview of these arguments first.
[Subtleties]
A 1st-order phase transition is not yet excluded and the quark-hadron continuity could be violated by topological probes such as vortices. This subtlety is not clarified but is extremely interesting. I will propose a possible resolution in this talk.
[Gravitational Wave Signal]
One might think that a smooth and continuous change to quark matter is difficult to see, but the pQCD EOS branch is very soft, and the EOS below the quark matter onset should thus be stiff, inevitably leading to rapid softening. I will show that the post-merger gravitational wave signal is sensitive to the EOS softening, so that properties of quark matter can be sufficiently quantified.
[Interpretation]
There are still uncertainties and it is important to identify the robust predictions. I will discuss the interpretation of our results of the gravitational wave signal and also point out that further constraints could be available from electromagnetic signals.
In our previous work, we have been using Lattice results and Polyakov Loop model to explore the non-perturbative dark deconfinement-confinement phase transition and the generation of gravitational-waves in a dark Yang-Mills theory. In this work, We further include fermions with different representations in the dark sector. Employing the Polyakov-Nambu-Jona-Lasinio (PNJL) model, we discover that the relevant gravitational wave signatures are highly dependent on the various representations. We also find a remarkable interplay between the deconfinement-confinement and chiral phase transitions. In both scenarios, the future Big Bang Observer experiment has a higher chance to detect the gravitational wave signals.
We propose a programme towards the understanding of confinement in QCD by means of the development of a geometrical version of the renormalization group flow for the Standard Model of Particle Physics. This is based on a stochastic version of the Ricci flow, which encodes both changes of topology and topological braiding. The proposed formalism enables the rescaling of fixed topologies through conformal transformations, while complementing the renormalization group flow in interacting contexts. The complementary stochastic quantization method a la Ricci that is proposed can be applied to the Wilsonian formulation of Yang-Mills theories, considering their background interaction with the gravitational field that affects the electric and magnetic Yang-Mills configurations, and re-interpreting matter interaction in terms of geometric quantities. We finally discuss how to apply this framework in order to provide a proposal for QCD confinement.
In order to understand the puzzle of the free energy of an individual quark in QCD, we explicitly construct ensembles with quark numbers $N_V\neq 0\!\!\mod\! 3$, corresponding to non-zero triality in a finite subvolume $V$ on the lattice. We first illustrate the basic idea in an effective Polyakov-loop theory for the heavy-dense limit of QCD, and then extend the construction to full Lattice QCD, where the electric center flux through the surface of $V$ has to be fixed at all times to account for Gauss's law. This requires introducing discrete Fourier transfroms over closed center-vortex sheets around the spatial volume $V$ between all subsequent time slices, and generalizes the construction of 't Hooft's electric fluxes in the purge gauge theory. We derive this same result from a dualization of the Wilson fermion action, and from the transfer matrix formulation with a local $\mathbb{Z}_3$-Gauss law to restrict the dynamics to sectors with the required center charge in $V$.
We test a method for computing the static quark-antiquark potential in lattice QCD, which is not based on Wilson loops, but where the trial states are formed by eigenvector components of the covariant lattice Laplace operator. The runtime of this method is significantly smaller than the standard Wilson loop calculation, when computing the static potential not only for on-axis, but also for many off-axis quark-antiquark separations, i.e., when a fine spatial resolution is required. We further improve the signal by using multiple eigenvector pairs, weighted with Gaussian profile functions of the eigenvalues, providing a basis for a generalized eigenvalue problem (GEVP). We show results with the new method for the static potential with dynamical fermions and demonstrate its efficiency compared to traditional Wilson loop calculations. The method presented here can be also applied to compute hybrid or tetra-quark potentials and to static-light systems.
We study new symmetries of the Cardy-Rabinovici model and their dynamical applications. The Cardy-Rabinovici model is a 4d $U(1)$ gauge theory with electric and magnetic matters, which is a good playground for studying the dynamics of the Yang-Mills theory with $\theta$ angle. In this model, the electromagnetic $SL(2, \mathbb{Z})$ self-duality is not realized in a naive way. Still, the $SL(2, \mathbb{Z})$ transformations become legitimate duality operations by appropriately gauging the $\mathbb{Z}_N$ 1-form symmetry. We construct new noninvertible symmetries from this duality at self-dual points and determine their non-group-like fusion rules. As an application, we can rule out the trivially gapped phase for some self-dual parameters due to a mixed gravitational anomaly of this new symmetry. We also show how the conjectured phase diagram of the Cardy-Rabinovici model is consistent with this anomaly matching condition. This talk is based on arXiv:2204.07440.
In this talk I will discuss how one can be more differential in
event-shape distributions by measuring the angle defined by the thrust axis
and the beam. As was shown in an earlier publication, the angular
dependence can be parametrised in terms of the well-known angular-averaged
cross section and the so called “angular” distribution. I will show that,
even though for jets initiated by light quarks the angular distribution
starts at O(alphaS), quark mass effects bring a non-vanishing contribution
already at at O(alphaS^0), making it a potential candidate for precision
measurements with flavour-tagged jets, and an important correction to the
massless limit. In the rest of the talk I will show how to setup the NLO
computation, highlighting how to analytically cancel the IR divergences
when adding up real- and virtual-radiation contributions, and show our
results. We find a universal coefficient for the plus function, a closed
integral form for the delta coefficient and a numerical result for the
non-singular terms that can be computed with high precision.
An array of high-priority HEP measurements are increasingly limited by the
precision of nucleon and nuclear parton distribution functions (PDFs) and
related quantities. Curiously, as the accuracy of perturbative QCD
calculations steadily improves, there is a growing need for parallel
enhancements to control a variety of nonperturbative QCD, electroweak, and
methodological effects in global PDF fits. In this talk, I will highlight a
number of recent cross-cutting developments in these areas spanning nucleon
and nuclear PDFs; I will also emphasize the potential for a combination of
future data from the LHC and EIC to drive further theory developments for
hadron structure.
Factorization theorems are known to be extremely powerful tools in high-energy particle physics. Processes like SIDIS, Drell-Yan vector-boson production, Higgs-boson production through gluon fusion and $e^+e^-$ to jets and/or hadrons are just some examples of processes that have been thoroughly investigated by applying rigorous factorization formulae. Furthermore, if in these processes the transverse momentum $\textbf{q}_T$ of the vector boson or final-state hadrons is measured, in the limit of small $\textbf{q}_T$, leading-power transverse-momentum-dependent (TMD) factorization is an established tool to obtain further insight into the internal structure of hadrons (like spin and helicity distributions, sea quark contributions) and/or jets involved. However, in order to properly exploit increasingly precise experimental data, it is important to investigate sub-leading contributions. In this talk, we present a novel method to compute next-to-leading-power and next-to-next-leading-power contributions to TMD cross sections. In the specific example of a Drell-Yan process, we show how our analytic results allow us to achieve next-to-next-to-leading logarithmic (NNLL) resummation, recover both the leading-power TMD factorization and collinear factorization expressions up to next-to-next-to-leading order in the small $\textbf{q}_T$ limit and provide a description of the cross section valid also at intermediate $\textbf{q}_T$. The implications for the phenomenological extraction of TMDPDFs are also discussed.
We review the status of tensions in the flavour sector, with particular
attention to semileptonic BBB decays and ∣Vxb∣|V_{xb}|∣Vxb∣
determinations.
In the context of lepton flavor universality violation (LFUV) studies, we study different observables related to the $b\to c\tau \bar{\nu}_\tau$ semileptonic decays. These observables are expected to help in distinguishing between different NP scenarios. Since the $\tau$ lepton is very short-lived, we consider three subsequent $\tau$-decay modes, two hadronic $\pi\nu_\tau$ and $\rho\nu_\tau$ and one leptonic $\mu\bar{\nu}_\mu\nu_\tau$, which have been previously studied for $\bar{B} \to D^{(*)}$ decays. This way the differential decay width can be written in terms of visible (experimentally accessible) variables of the massive particle created in the $\tau$ decay. There are seven different $\tau$ angular and spin asymmetries that are defined in this way and that can be extracted from experiment. In addition to these asymmetries, we study the $d^2\Gamma_d/(d\omega d\cos\theta_d)$, $d\Gamma_d/d\cos\theta_d$ and $d\Gamma_d/dE_d$ distributions. We present numerical results for the $\Lambda_b\to\Lambda_c\tau\bar{\nu}_\tau$ semileptonic decay, which is expected to be measured with precision at the LHCb.
Charged mesons in the charmonium mass region are a clear indication of the existence of states beyond the naive quark model. After the discovery of the Zc(3900) and Zc(4020) by the BESIII and Belle Collaborations, the Zcs(3985) was discovered by the BESIII Collaboration in the K+ recoil mass spectrum in e+e- collisions.
A natural explanation of the Zc states in the quark model can be obtained as charmed meson molecules, that allows to introduce the neccessary light degrees of freedom, since the states are close to these thresholds. If one then change a light quark by an strange quark, one should expect to have some strange partners.
In this contribution we will show the results of such a picture in a chiral quark model that have been widely use in the study of heavy hadrons.
Stunning discoveries of the hadronic states that are manifestly different to the conventional meson and baryons have energized the field of spectroscopy in recent years. New exotic states keep appearing thanks to the excellent detector performance of the LHCb experiment and scrupulous data analysis. In this talk, fresh findings on the heavy-flavour pentaquarks and tetraquark families at LHCb will be discussed.
This talk will summarise the experimental status on jet measurements in heavy-ion collisions.
Over the last decades, the theoretical picture of how hadronic jets interact with nuclear matter has been extended to account for the medium’s finite longitudinal length and expansion. However, only recently a first-principle approach has been developed that allows to couple the jet evolution to the medium flow and anisotropic structure in the dilute limit. In this talk, we will show how to extend this approach to the dense regime, where the resummation of multiple in-medium scatterings is necessary. Particularly, we will consider the modifications of the single particle momentum broadening distribution and single gluon production rate in evolving matter. The resummation is performed by either computing the opacity series or starting from the all order BDMPS-Z formalism. We will also discuss the (novel) resulting modifications to jets' substructure.
As a consequence of the theoretical improvements and the wide range of accurate experimental measurements, our understanding of the collective phenomena in heavy-ion collisions has advanced significantly over the past years. The Global Bayesian analysis played a substantial role in this advancement. In this talk, we present a global Bayesian analysis to infer the transport properties of Quark-Gluon Plasma, using the latest Large Hadron Collider Pb-Pb data at $\sqrt{s_{\text{NN}}}$=2.76 and 5.02 TeV. We show that including the latest multi-harmonic flow measurements significantly improves the uncertainties of the inferred specific shear and bulk viscosities. This observation shows the necessity of accurate measurements of collective flow independent observables in the future. We also discuss the challenges in modeling the observed flow-like signals in the small systems including some results from the Bayesian analysis and its prospects for future improvements.
Comparing the complex structure of the models of the quark gluon plasma is a useful way to better discern the physics following a heavy ion collision, in particular in the vicinity of a phase transition. In this talk, I will focus on quasinormal modes and the collisions of poles in the complex plane, first by using the chiral phase transition as an illustrative example (2005.02885,2101.10847,2111.03640). Then, recognizing the interplay between weak and strong coupling sectors in a typical collision, I will introduce a hybrid model with a weakly broken symmetry (2108.02788) which has a rich quasi-hydrodynamic phenomenological description where hydrodynamic and non-hydrodynamic poles are unified by a common dispersion relation. I will show that energy transfer occurs initially from the soft to the hard sector before irreversibly transferring back to the soft sector at late times, and that the model reproduces many features common to dissipative systems with a weakly broken symmetry including the k-gap.
Local quantum field theory (QFT) provides a framework for establishing the non-perturbative constraints imposed on finite-temperature correlation functions. In this talk I will discuss how the locality of fields has significant implications for the spectral properties of finite-temperature QFTs, in particular that the peak-broadening effects experienced by particle states can be directly extracted from imaginary-time correlation functions. As an application, I discuss the calculation of the pion spectral function from Euclidean data.
We analyze the sensitivity of the rare decays $\eta^{(\prime)}\to\pi^{0}\gamma\gamma$ and $\eta^{\prime}\to\eta\gamma\gamma$ to GeV-signatures of a leptophobic $B$ boson.
A controlled theoretical description of the amplitudes, based on vector meson dominance and the linear sigma model, along with the current experimental data, has allowed us place limits on the $B$ boson properties, i.e. baryonic gauge coupling $g_{B}$, mass and width.
While the discovery potential offered by these processes is very promising, the experimental situation is not conclusive and it will not be possible to make a categorical statement until the arrival of new and more precise data, e.g. from the KLOE and JEF experiments.
In the present work, we have studied the T-even subleading twist TMDs in the light-front quark-diquark model. Exclusively, we have studied their relations with the leading twist TMDs in the same model and, the question, how such relations are model (in)dependent, is discussed. We have also compared our results with the other quark models.
In this talk, we will discuss the BFKL leading logarithmic resummation, relevant for the Regge limit behavior of QCD scattering amplitudes, in the IR regulated effective action, which satisfies exact functional renormalization group equations. Using this framework we study, in the high-energy limit and at larger transverse distances the transition to a much simpler effective local Reggeon field theory, and investigate the critical properties. Moreover, we perform numerical analysis of the spectrum of the BFKL Pomeron by the introduction of a Wilsonian infrared regulator to understand the properties of the leading poles (Pomeron states) and its contribution to the high-energy scattering
We outline the role that an early deconfinement phase transition from normal nuclear matter to a color superconducting quark-gluon plasma phase plays for the phenomenology of supernova explosions and binary neutron star mergers. To this end we extend the compact star equation of state (EoS) from vanishing to moderately high temperatures that become accessible in the CBM experiment at FAIR. We study the connection of such hybrid EoS with the mass-radius relation of cold compact stars, including the intriguing possibility of additional families, as a consequence of the presence of an early and strong phase transition. Special emphasis is devoted to the simultaneous fulfillment of the new NICER mass and radius constraint from PSR J0740+6620 and the tidal deformability constraint from GW170817 which require the EoS to be soft at about twice saturation density and then to stiffen. Such a pattern is provided by an early and strong deconfinement transition. Dynamical scenarios are being considered, such as binary compact star mergers including the subsequent emission of gravitational waves and supernova explosions of massive supergiant stars where neutrinos play the role of messengers.
Black hole–neutron star mergers (BHNS) are astrophysical phenomena of great interest because they not only produce gravitational-wave signals but also can have very energetic electromagnetic counterparts in particular in the form of kilonova explosions. The disruption of the neutron star produces the dynamical ejection of some material and the formation of a disk of hot matter around the black hole, and, in turn, these processes can be at the origin of a kilonova (KN) signal. The amount of ejected material is directly related to the stiffness of the equation of state (EoS). We compare the predictions obtained by considering equations of state of neutron star matter satisfying the most recent NICER observations (J0740+6620) and assuming that only one family of compact stars exists with the results predicted in the two-families scenario. In the latter a soft hadronic equation of state produces very compact stellar objects, while a rather stiff quark matter equation of state produces massive strange quark stars, satisfying NICER results. The expected KN signal in the two-families scenario is very weak: in particular, the hadronic star–black hole merger produces a much weaker signal than in the one-family scenario because the hadronic equation of state is very soft. Moreover, according to the only existing simulation, the strange quark star–black hole merger does not produce a KN signal because the amount of mass ejected is negligible.
The fundamental constituent of matter at high temperature and density has intrigued physicists for quite some time. Recent results from heavy-ion colliders have enriched the Quantum Chromodynamics (QCD) phase diagram at high temperature and low baryon density. However, the phase at low temperature and finite (mostly intermediate) baryon density remain unexplored. Theoretical QCD calculation predicts phase transition (PT) from hadronic matter (HM) to quark matter (QM) at such densities. Presently, the best labs available to probe such densities lie at the core of neutron stars (NSs). In this presentation, I will present our recent results of how such PT signatures can be probed using gravitational waves (GWs) both in isolated NSs and NSs in binaries. The isolated NS would probe the very low-temperature regime whereas NSs in binaries would probe finite baryon density in the intermediate temperature regime. We would also discuss whether the GW signature of such PT is unique and the detector specification needed to detect such signals.
We analyze the recent astrophysical constraints in the context of a hadronic equation of state (EoS) in which the baryonic matter is subject to chiral symmetry restoration. We show that with such EoS it is possible to reconcile the modern constraints on the neutron star (NS) mass, radius, and tidal deformability (TD). We find that the softening of the EoS, required by the TD constraint of a canonical $1.4 M_\odot$ NS, followed by a subsequent stiffening, required by the $2M_\odot$ constraint, is driven by the appearance of $\Delta$ matter due to partial restoration of chiral symmetry. Consequently, a purely hadronic EoS that accounts for the fundamental properties of quantum chromodynamics linked to the dynamical emergence of parity doubling with degenerate masses of nucleons and $\Delta$ resonances can be fully consistent with multi-messenger data. Therefore, with the present constraints on the EoS, the conclusion about the existence of quark matter in the stellar core may still be premature.
The D0-matrix models of string theory have gained much attention in the latter years. I will discuss the physics one can extract from these using lattice-based simulations and the gauge/gravity duality to understand gravitational theories. In particular, I will show how the confinement-to-deconfinement transition corresponds to a topology change of the geometry in the supergravity theory and how at low temperatures conforms to the study of the M-theory region.
Beyond the standard model theories involving early universe first order phase transitions can lead to a gravitational wave background that may be measurable with improved detectors. Thermodynamic observables of the transition, such as the latent heat, determined through lattice simulations can be used to predict the expected signatures from a given theory and constrain physical models. Metastable dynamics around the phase transition make precise determination of these observables difficult and often lead to large uncontrolled numerical errors. In this talk, I will discuss a prototype lattice calculation in which the first order deconfinement transition in the strong Yang-Mills sector of the standard model is analysed using a novel lattice method, the logarithmic linear relaxation method. This method provides a determination of the density of states of the system with exponential error suppression. From this, thermodynamic observables can be reconstructed with a controlled error, providing a promising direction for accurate model predictions.
Many models of composite dark matter feature a first-order confinement transition in the early universe, which would produce a stochastic background of gravitational waves that will be searched for by future gravitational-wave observatories. I will present work in progress using lattice field theory to predict the properties of such first-order transitions. Targeting SU(N) Yang-Mills theories, this work employs the Logarithmic Linear Relaxation (LLR) density of states algorithm to avoid long autocorrelations at the transition.
We study the thermal transitions of dense two colour QCD with two flavours of Wilson fermions at a fixed chemical potential $\mu=443$MeV on a coarse isotropic lattice $a=0.18$fm.
The results on a larger lattice volume ($N_s=24$) are compared with earlier results with the same lattice spacing but a smaller lattice volume ($N_s=16$). Only small finite volume effects are found.
We also present first results from simulations with a finer lattice spacing and lighter quarks than previously studied.
In view of the usually encountered complexity of the quantum-field-theoretic approach to (two-particle) bound states by means of the homogeneous Bethe‒Salpeter equation, this formalism is frequently subjected to various simplifying approximations. If carried to its extremes, this procedure ultimately yields semirelativistic equations of motion believed to reproduce, at least coarsely, the basic features of the bound-state solutions sought. Whether or not this belief is justified may be scrutinized by taking into account a couple of evident boundary conditions on the predicted discrete spectra, expected to hold on rather general grounds and straightforwardly applicable as soon as the underlying interaction has been specified.
The magnetic fields generated in non-central heavy-ion collisions are among the strongest fields produced in the universe, reaching magnitudes comparable to the scale of strong interactions. Backed by model simulations, the resulting field is expected to be spatially modulated, deviating significantly from the commonly considered uniform profile. In this work, we present the next step to improve our understanding of the physics of quarks and gluons in heavy-ion collisions by adding an inhomogeneous magnetic background to our lattice QCD simulations. We simulate $2+1$ staggered fermions with physical quark masses for a range of temperatures covering the QCD phase transition. We assume a $1/\cosh(x)^2$ function to model the field profile and vary its strength to analyze the impact on the chiral condensate and the Polyakov loop. These order parameters show non-trivial spatial features due to the interplay between the sea and the valence effects as the system approaches the crossover temperature. After the continuum limit extrapolation, we use these quantities to draw the phase diagram in the $T$-$B$ plane and understand the implications of an inhomogeneous $B$ to QCD physics. We also find that in this set-up, the system develops steady electric currents which flow in equilibrium. We use these currents to present our new method of obtaining the magnetic susceptibility of the QCD medium and compare it to previously established methods.
In this article [1], we have explored the very important quantity of lepton pair production from a hot and dense QCD medium in presence of an arbitrary magnetic field for simultaneous nonzero values of both the parallel and perpendicular components of momentum. As opposed to the zero magnetic field case (the so-called Born rate) or the lowest Landau level approximated rate, where only the annihilation process contributes, here we observe contributions also arising out of the quark and antiquark decay processes. We found the encouraging result of considerable enhancement of lepton pair production in presence of a magnetic field. We further decompose the total rate into different physical processes and make interesting observations for both zero and nonzero baryon density. The whole analysis is then subjected to an effective model treatment, which leads us to some further interesting observations.
Aiming at a self-consistent description of multiquark hadrons (such as tetraquarks, pentaquarks, hexaquarks, etc.) by means of QCD sum rules, we note that the entirety of contributions to two- or three-point correlation functions involving, respectively, two or one multiquark interpolating operators may be straightforwardly disentangled into two disjoint subsets comprising of unambiguously identifiable members:
• On the one hand, there are all those “multiquark-phile” contributions that indeed may support the multiquark state of interest. In the case of flavour-exotic tetraquarks, by definition composed of four (anti-)quarks of mutually different flavours, such tetraquark-phile contributions necessarily involve at least two gluon exchanges of appropriate topology.
• On the other hand, there are all those contributions that definitely do not bear any relation to the multiquark in the focus of interest and, consequently, should be discarded from one’s multiquark analysis by application of some QCD sum-rule formalism.
Needless to say, exclusively the former subset should enter any “multiquark-adequate” QCD sum-rule description of exotic hadrons.
We study the production of charm quarks in hot QCD medium utilizing the quasiparticle model (QPM). The deconfined matter is composed of the dynamical quarks and gluons dressed by the effective temperature-dependent masses. The temperature dependence is specified by a running coupling deduced from lattice QCD thermodynamics [1]. For the evolution of the QGP, we employ the results of hydrodynamic simulations [2] incorporating the shear viscosity computed in the quasiparticle model [3].
In heavy nuclei, the distribution of neutrons extends out further than the proton distribution forming a so-called “neutron skin”. An accurate experimental determination of the neutron skin thickness of heavy nuclei would provide a unique constraint on the symmetry energy of the nuclear Equation Of State, which strongly depends on poorly constrained three-body forces. Photons have an advantage over other nuclear probes for this purpose since they can interact with the whole volume of the nucleus. Consistently, coherent neutral pion photoproduction on nuclei is sensitive to the distribution of nucleons. The information on the neutron distribution can be extracted by comparing the diffraction pattern of the measured photoproduction cross section with theoretical calculations.
The method of coherent pion photoproduction provides an efficient tool to study the neutron skin however requires a reliable theoretical model. Because the cross section is strongly affected by final-state interactions of the pion on the way out of the nucleus, this effect has to be accounted for in the model calculations.
Our goal is to build a universal model that describes both pion scattering and photoproduction.
In this work, we develop a new momentum space model in the distorted wave impulse approximation framework. To reliably account for the pion-nucleus final-state interaction, we design the effective second-order pion-nucleus potential, which includes analysis of the in-nuclear medium the Delta(1232) self-energy modification by fitting pion-carbon scattering data. In the following, the pion-nucleus potential not only participates in calculating the effect of the final state interaction but also is the base for constricting in-medium modified photoproduction amplitude.
We use complex Langevin simulations to study the QCD phase diagram with two light quark flavours. In this study, we use Wilson fermions with an intermediate pion mass of ~500 MeV. By studying thermodynamic quantities, in particular at lower temperatures, we are able to describe the equation of state.
We present a novel strategy to strongly reduce the severity of the sign problem, using line integrals along paths of changing imaginary action. Highly oscillating regions along these paths cancel out, decreasing their contributions. As a result, sampling with standard Monte-Carlo techniques becomes possible in cases which otherwise requires methods taking advantage of complex analysis, such as Lefschetz-thimbles or Complex Langevin. We lay out how to write down an ordinary differential equation for the line integrals. As an example of its usage, we apply the results to a 1d quantum mechanical anharmonic oscillator with a $x^4$ potential in real time, finite temperature.
We present a data-driven analysis of the $\gamma\gamma\to D^+D^-$ and $\gamma\gamma\to D^0\bar{D}^0$ reactions from threshold up to 4.0 GeV in the $D\bar{D}$ invariant mass. For the $S$-wave contribution, we adopt a partial-wave dispersive representation, which is solved using the $N/D$ ansatz. The left-hand cuts are accounted for using the model-independent conformal expansion. The $D$-wave $\chi_{c2}(3930)$ state is described as a Breit-Wigner resonance. The resulting fits are consistent with the data on the invariant mass distribution of the $e^+e^- \to J/\psi D\bar{D}$ process. Performing an analytic continuation to the complex $s$-plane, we find no evidence of a pole corresponding to the broad resonance $X(3860)$ reported by the Belle Collaboration. Instead, we find a clear bound state below the $D\bar{D}$ threshold at $\sqrt{s_B} = 3695(4)$ MeV, confirming the previous phenomenological and lattice predictions.
The complexity of strong dynamics has triggered many different techniques used depending on the phenomena to be described. Often, they rely on quantization over the plane of constant time in Minkowski space, but there are other possibilities: when quantization is carried out over a light front, the theory is manifestly invariant under the boost transformation along the direction of the light-front and the structure of the groundstate simplifies, since the vacuum decouples. These simplifications make it easier to consider Hamiltonianeigenvalue problems and give rise to the front-form of Hamiltonian dynamics, which can be used to study QCD bound-state problems [1].
However, the Hamiltonians obtained after a canonical quantization procedure are very badly divergent and regularization parameters and counterterms are needed. The renormalization group procedure for effective particles, RGPEP [2, 3, 4], was developed by Głazek and Wilson to obtain finite, physical predictions using effective particles of size s with interactions that are suppressed if the energy scale of the process is greater than a chosen λ = 1 s.
The RGPEP has been successfully applied to derive asymptotic freedom from the coefficients of the three gluon-vertex functions in purely gluonic QCD [3, 5] using ultraviolet and small-x cutoffs, albeit with an undesired finite dependence on the running coupling constant. To avoid this dependence new regularization schemes need to be explored and this poster describes one of such schemes, deriving asymptotic freedom with a canonical gluon mass term as regulator and using the same regularization functions to avoid both ultraviolet and small-x divergences.
The ghost propagator in Landau gauge is studied at finite temperature below and above $T_c$ using lattice QCD simulations. For high temperatures, we find that the ghost propagator is enhanced, compared to the confined phase. The results suggest that the ghost propagator can be used to identify the phase transition, similarly to the gluon propagator case.
We explore the consequences of gluonic hot spots in the proton for coherent and incoherent exclusive vector meson production cross sections. For the proton we use the Color Glass Condensate framework in the dilute limit with Gaussian hot spots of fluctuating color charges, which we are able to average over analytically. The cross sections are computed using the lowest order dipole model and the vector meson wave function is are taken to be non-relativistic. We find that the coherent cross section is sensitive to both the size of the target and the structure of the probe. The incoherent cross section is dominated by color fluctuations at small transverse momentum transfer ($t$), by proton and hot spot sizes as well as the structure of the probe at medium $t$ and again color fluctuations at large $t$. While the $t$-dependence of the cross section is well reproduced by our model, the relative normalization between the coherent and the incoherent cross sections points to the need for additional fluctuations in the proton.
We report novel lattice QCD results for the three-gluon vertex from quenched lattice-QCD simulations. Using standard Wilson action, we have computed the three gluon vertex beyond the usual kinematic restriction to the symmetric (q² = r² = p²) and soft-gluon (p = 0) cases where it depends on a single momentum scale. We will present a detailed analysis of the asymmetric case (r² = q² ≠ p²) where the transversely projected vertex can be cast in terms of three independent tensors.
The lattice data show a clear dominance of the form-factor corresponding to the tree-level tensor.
For the general kinematical configuration (q² ≠ r² ≠ p²); we have computed the projection of the three-gluon vertex providing the relevant information on the ghost-gluon kernel-related function W(q²).
that appears in the recently discussed smoking-gun signals of the
Schwinger mechanism in QCD. This projection exhibits a striking scal-
ing in terms of (q² + r² + p²)/2.
One of the main subjects in current nuclear physics is to reveal rich
phase structure in high baryon density matter: the first-order chiral
transition line with the QCD critical point (CP), the color
superconducting (CSC) phase transition and so on. In the present
contribution, we calculate how the critical fluctuations that develop
around the QCD CP and CSC phase transition, affect the experimental
observables and transport phenomena based on the two-flavor NJL model.
We consider the Aslamazov-Larkin, Maki-Thompson, and Density of States
terms due to critical fluctuations, which are known to give rise to
anomalous excess of electric conductivity in metals in the vicinity of
the critical temperature of superconductivity. The results show that the
dilepton production rate is enhanced in the low invariant mass region
and that the transport coefficients, such as the electric conductivity,
the relaxation time, and the diffusion constant, diverge at the critical
temperatures. We shall explain the differences of the results between
the two systems and discuss that these results would be detectable as
the experimental signal for each phase transition in the heavy-ion
collision experiments.
Strongly coupled matter called quark–gluon plasma (QGP) is formed in heavy-ion collisions at RHIC and the LHC. The expansion of this matter, caused by pressure gradients, is known to be hydrodynamic. The computations show that the expanding QGP has a small shear viscosity to entropy density ratio (η/s), close to the known lower bound 1/4π. In such a medium one expects that jets passing through the medium would create Mach cones. Many experimental trials have been done but proper evidence of the Mach cone has not been found yet [1, 2]. The Mach cones were thought to cause double-bumps in azimuthal correlations. However, these were later shown to be the third flow harmonic.
In our study, a new method is proposed for finding the Mach cone with so called event-selection-engineering. The higher order flow harmonics and their linear response are known to be sensitive to the medium properties. Hence a Mach cone produced by a high momentum jet would change the system prop- erties and, thus, the observable yields. Different flow observables are studied by selecting high energy jet events with various momentum ranges. Considered observables for different momenta are then compared to the nominal events.
We report differences in the flow harmonics and their correlations to sepa- rate jet momenta which showcase a clear evidence of Mach cone formation in the heavy-ion collisions. The observations of various jet momenta are then quanti- fied with χ2-test to see the sensitivities of different observables to momentum selections.
References
[1] K. Aamodt et al. Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at √sNN=2.76 TeV. Phys. Rev. Lett., 107:032301, 2011.
[2] A. Adare et al. Transition in Yield and Azimuthal Shape Modification in Dihadron Correlations in Relativistic Heavy Ion Collisions. Phys. Rev. Lett., 104:252301, 2010.
When colliding heavy ions, like Pb-Pb at the LHC, it is known that long-range
correlations is a collective flow effect of the quark gluon plasma produced in the
collision. Similar effects have also been observed in smaller collision systems such as
p-Pb and pp at the LHC. The origin of these long-range correlations in small systems,
and whether it is the same as in large collision systems, are still not well understood.
The non-flow effects, such as jets, get larger in small systems and make the
measurements difficult. Hence the goal is to examine the methods where the non-flow
effects are properly subtracted: the enhanced away-side jet yields in high-multiplicity
with respect to low-multiplicity events. At the same time,
different experiments use different kinematic cuts for both multiplicity and interested particles, which make
comparison between experiments difficult, even though the same method is used.
In this poster, we will present the current status of the method and verification,
and show some of the obtained measurements. In addition, we address how the above
mentioned kinematic cuts might affect the interpretation of the results.
We show that the recent ALICE measurement of the hadronic lead-lead cross section implies a small nucleon width, which is inconsistent with all state-of-the-art current global analyses of a wide set of experimental results. This inconsistency has several consequences for global analyses, both at a fundamental level as well as for quantities such as the bulk viscosity. The updated global Bayesian framework provides a better description of triple-differential observables such as the correlation between mean transverse momentum and anisotropic flow.
The present information about neutron star radii and masses imply that the EOS should not be too stiff around densities corresponding to the hyperon (and/or Delta) onset at 1.4 M_sun, but should then stiffen in order to reach (and exceed) masses of 2.0 M_sun at radii of about 12 km or larger.
Is such a pattern compatible with a purely hadronic EOS? Or does it imply an early, strong deconfinement transition to quark matter that stiffens with increasing density?
As the maximum energy density reached in the very core of massive neutron stars is below about 2 GeV/fm3, a factor 20 below the range where perturbative QCD is applicable, how can pQCD nevertheless constrain the neutron star EoS?
What constraints for the hadron-to-quark matter transition can be derived from NS observations? How likely is a crossover transition at low temperatures which could imply a second critical endpoint or even a crossover-all-over in the QCD phase diagram?
These are questions to be discussed by the panelists together with the audience of QCHS-XV.
In gauge Higgs theories there is the possibility that there may exist localized excitations of the gauge and Higgs fields surrounding a static charge, and this would lead to excited states of what are usually described as "elementary" particles. This possibility is illustrated by a numerical simulation of the Landau-Ginzburg model of superconductivity, which in turn suggests certain experimental tests. Similar numerical results in other gauge Higgs theories are briefly reviewed.
We systematically explore real and complex saddle points for the Hubbard model on hexagonal lattice at zero and non-zero chemical potential. As a result of this study, we formulate the saddle point approximation to the path integral, which is essentially the gas of weakly interacting instantons. Since bosonic part of the action is Gaussian, Euclidean field equations for instantons should necessarily include back-reaction from fermionic determinant to describe any non-trivial solution. We follow this route and give approximate analytical description for these instantons.
We formulate a classical partition function for the instanton gas, that has predictive power. For a given parameter set, we can predict the distribution of instantons and show that the instanton number is sharp in the thermodynamic limit, thereby defining a unique dominant saddle point. This knowledge can be subsequently used to predict the dominant thimble for the path integral at finite chemical potential and to substantially weaken the sign problem.
We also study the physical properties of the instanton gas approximation. It fails to capture the magnetic transition inherent to the Hubbard model on the honeycomb lattice, but captures local moment formation. In fact, an instanton corresponds to local moment formation and concomitant short ranged antiferromagnetic correlations. This aspect is also seen in the single particle spectral function extracted from the instanton gas approximation that shows clear signs of the upper and lower Hubbard bands and bears striking similarities with the exact results obtained using Quantum Monte Carlo simulations.
As further perspectives, we discuss the possibilities for systematic improvements by taking into account fluctuations around the dominant multi-instanton saddle point field configuration.
After a brief historical review of the $\alpha_s$ determination from tau decay and the difficulty of dealing with Duality Violations and the associated asymptotic nature of the OPE which was present in previous analyses, I will describe a new determination of the strong coupling constant based on an improved vector isovector spectral function. This spectral function results from combining ALEPH and OPAL distributions for the leading 2 and 4 pion channels with estimates of subleading contributions from e+e- by using CVC, which are accurate up to numerically irrelevant isospin-breaking corrections, and also the BaBar data for tau decay into kaon pairs. The resulting spectral function is thus based purely on experimental data and, unlike previous analyses, does not rely on Monte Carlo estimates. The new result for the strong coupling constant is $\alpha_s(m_{\tau}) = 0.3077 \pm 0.0075 $, which corresponds to $\alpha_s(m_Z ) = 0.1171 \pm 0.0010$.
Pinched Borel-Laplace sum rules are applied to ALEPH $\tau$-decay data. For the leading-twist ($D=0$) Adler function a renormalon-motivated extension is used, whose coefficient at $(\alpha_s/\pi)^5$ is taken according to the estimate $d_4=275 \pm 63$. Two terms of dimension $D=6$ are included in the truncated OPE ($D \leq 6$), in order to enable cancellation of the corresponding renormalon ambiguities. The effective leading-order anomalous dimensions of the $D=6$ OPE operators have noninteger values (beyond large-$\beta_0$). Two variants of the fixed order perturbation theory, and the inverse Borel transform, are applied to the evaluation of the $D=0$ contribution. Truncation index $N_t$ is fixed by the requirement of local insensitivity of the momenta $a^{(2,0)}$ and $a^{(2,1)}$ under variation of $N_t$. The averaged value of the coupling obtained is $\alpha_s(m_{\tau}^2)=0.3179^{+0.0051}_{-0.0088}$ [$\alpha_s(M_Z^2)=0.1184^{+0.0007}_{-0.0011}$]. The theoretical uncertainties are significantly larger than the experimental ones.
In my talk, I will present a data-driven coupled-channel analysis of the isoscalar S-wave {$\pi\pi,KK$} scattering using the partial-wave dispersion relations. The central result is the Omnes matrix, which does not have left-hand cuts, and therefore serves as the crucial input needed to study the final state interactions of any hadron processes where the system of two pions (and two kaons) shows up. As an application, I will show our recent results on $e^+e^-→J/\psi \pi\pi(KK)$ and $\gamma^*\gamma^*\to \pi\pi(KK)$ scattering. The input from the latter allowed us to perform a dispersive estimation of the $f_0(980)$ contribution to $(g-2)_\mu$. My talk will be based on [2012.11636, 2004.13499, 2004.13499, 1909.04158].
In the 1960’s Weinberg proposed a way to discriminate between molecular and compact near-threshold bound states in the weak-binding limit. We discuss a generalisation of this criterion which can be employed to characterise the compositeness of bound, virtual and resonance states [1]. In addition, the relevant modifications in the presence of coupled channels, isospin violations and unstable constituents are reviewed [2]. A clear recipe how to relate the scattering length and effective range extracted from a fit to experimental data to the ones to be used in the Weinberg criterion is provided.
[1] I.Matuschek, V.Baru, F.-K.Guo, and C.Hanhart, Eur. Phys.J.A 57 (2021) 3, 101
[2] V.Baru, X.K.Dong, M.L.Du, A.Filin, F.K.Guo, C.Hanhart, A.Nefediev, J.Nieves and Q.Wang, e-Print: 2110.07484 [hep-ph] to be published in Phys. Lett. B
The double-charm tetraquark meson $T_{cc}^+(3875)$ can be produced in high-energy proton-proton collisions by the creation of the charm mesons $D^{*+} D^0$ at short distances followed by their binding into $T_{cc}^+$. The $T_{cc}^+$ can also be produced by the creation of $D^{*+} D^{*+}$ at short distances followed by their rescattering into $T_{cc}^+ \pi^+$. A charm-meson triangle singularity produces a narrow peak in the $T_{cc}^+ \pi^+$ invariant mass distribution 6.1 MeV above the threshold with a width of about 1 MeV. Well beyond the peak, the differential cross section decreases with the invariant kinetic energy $E$ of $T_{cc}^+ \pi^+$ as $E^{-1/2}$.
Our estimate of the cross section for $T_{cc}^+ \pi^+$ from the triangle-singularity peak is large enough to encourage the effort to observe the peak at the LHC. The observation of such a peak would provide strong support for the identification of $T_{cc}^+$ as a loosely bound charm-meson molecule.
*This work was supported in part by the U.S. Department of Energy, by the National Natural Science Foundation of China (NSFC), by the Natural Science Foundation of Shandong Province of China, and by NSFC and the Deutsche Forschungsgemeinschaft through the Sino-German Collaborative Research Center.
The medium that forms in a heavy-ion collision modifies the properties of jets traversing it. These modifications give substantial information about the nature of the medium and, therefore, they are one of the main focuses of the heavy-ion program at LHC. The influence of the medium into highly energetic partons depends on correlators of Wilson lines, which have been studied in perturbation theory and in several phenomenological models. In this talk, we focus on the antenna configuration, the study of the evolution of the large energy partons resulting from a collinear splitting inside of the medium. In the eikonal limit, the interaction of each daughter parton with the medium can be parametrized by a light-like Wilson line in a given direction. We consider the case in which the angle between these two directions $\theta$ is small but such that $L\theta$ is of the order of the medium resolution scale, where $L$ is the size of the medium. We find that finite angle effects give sub-leading corrections to jet broadening. The physical effect in the antenna configuration is to make the decoherence effect larger when finite angle corrections are taken into account.
The fast development of quantum technologies over the last decades has offered a glimpse to a future where the quantum properties of multi-particle systems might be fully understood. In the context of jet quenching, quantum computers might allow for a better understanding of medium induced jet modifications which are hard to extract using traditional approaches. In this talk, I will focus on the leading order effect, momentum broadening. I will show how to formulate the real time evolution of a single particle jet in a dense medium in terms of quantum gate operations in a small set of qubits. The main focus will be put on the extraction of the jet quenching parameter $\hat q$. Numerical results for this coefficient are shown, being extracted from the quantum simulations performed using the IBM qiskit framework. Finally, I will explain how this approach can be extended to multi particle production and to jet evolution at early times in heavy ion collisions
Since our recent publication on direct CP violation and the Delta I = 1/2 rule in $K \to \pi\pi$ decay which was made with G-parity boundary conditions, we have revisited this problem with a conventional lattice setup employing periodic boundary conditions and two lattice spacings to check our previous result and to improve the precision. We show that the physical amplitude, which corresponds to an excited state in this case, can be obtained reliably with the Generalized Eigenvalue Problem (GEVP) method. Not only are periodic boundary conditions cheaper and allow the use of existing ensembles, but they provide a straightforward path to introduce electromagnetism and strong isospin symmetry breaking, which will be needed in the near future. In this talk, we show our preliminary results on $24^3$ and $32^3$ lattices with domain-wall fermions at physical masses and discuss the prospect of the high-precision calculation of $K \to \pi\pi$ decay with periodic boundary conditions.
Kaons participate in a number of flavour-changing neutral current decays that are highly suppressed in the Standard Model, which are therefore expected to be sensitive to new physics. Calculating the long-distance contributions to these decay modes is a challenging theoretical problem, and crucial for channels where these effects are dominant. Lattice QCD can provide a first-principles framework for exploring these phenomena, with the potential for input on a variety of observables and non-perturbative quantities. Such input will constitute important Standard Model comparisons with anticipated NA62 Run 2 and LHCb results. In this talk I will present the current state of lattice QCD calculations for rare kaon decays and discuss the future landscape for rare kaon lattice calculations.
Abstract: Formed in the aftermath of gravitational core-collapse supernova explosions, neutron stars are the most compact observed stars. Their average density exceeds that found inside the heaviest atomic nuclei. According to our current understanding, a neutron star is stratified into distinct layers. The surface is probably covered by a metallic ocean. The solid layers beneath consist of a crystal lattice of pressure-ionized atoms embedded in a highly degenerate relativistic electron gas. With increasing density, nuclei become progressively more neutron rich until neutrons start to drip out of nuclei thus delimiting the boundary between the outer and inner regions of the crust, where neutron-proton clusters are immersed in a neutron liquid. At about half the density of heavy nuclei, the crust dissolves into a homogeneous liquid mixture of nucleons and leptons. The region in between may consist of a liquid-crystal mantle of very exotic nuclear configurations. Adding nuclear shell and pairing effects perturbatively to the extended Thomas-Fermi approximation, we have recently found that these so called nuclear pastas might be less abundant than previously thought [1,2].
[1] J. M. Pearson, N. Chamel, A. Y. Potekhin, Phys. Rev. C 101, 015802 (2020)
[2] J. M. Pearson, N. Chamel, Phys. Rev. C 105, 015803 (2022)
The FSU2H equation of state model, originally developed to describe cold neutron star matter with hyperonic cores, is extended to finite temperature [1]. Results are presented for a wide range of temperatures and lepton fractions, which cover the conditionsmet in protoneutron star matter, neutron star mergers and supernova explosions. It is found that the temperature effects on thethermodynamical observables and the composition of the neutron star core are stronger when the hyperonic degrees of freedomare considered. An evaluation of the temperature and density dependence of the thermal index leads to the observation that theso-called Γ law, widely used in neutron star merger simulations, is not appropriate to reproduce the true thermal effects, specially when hyperons start to be abundant in the neutron star core.
[1] H. Kochankovski, A. Ramos and L. Tolos, 2206.11266 [astro-ph.HE]
We consider kinetic coefficients (thermal conductivity, shear viscosity, momentum transfer rates) of the magnetized neutron star cores within the framework of the Landau Fermi-liquid theory. We restrict ourselves to the case of normal (i.e. non-superfluid) matter and nucleonic composition. The magnetic field is taken to be non-quantizing. The presence of magnetic field leads to the tensor structure of kinetic coefficients. We find that the moderate ($B< 10^{12}$ G) magnetic field do not affect considerably thermal conductivity of neutron star core matter, since the latter is mainly governed by the electrically neutral neutrons. In contrast, shear viscosity is affected even by the moderate $B\sim 10^8–10^{10}$ G.
The uncertainties in the results are illustrated utilizing 39 equations of state from the CompOSE database and several models of the in-medium nucleon interactions treated via the Brueckner-Hartree-Fock calculations of the in-medium scattering matrices.
We also provide a "poor man" approximation for the transport coefficients based on the in-vacuum nucleon cross-sections which allow to obtain qualitatively correct results for any given nucleonic equation of state of the neutron star core.
The work is supported by RSF #19-12-00133
From the embedding of the Standard Model Effective Field Theory (SMEFT) in the more general Higgs Effective Field Theory (HEFT), we expose correlations among the coefficients of the latter that, if found to be violated in future data, would lead to the experimental falsification of the SMEFT framework. These are derived from the necessary symmetric point of HEFT and analiticity of the SMEFT Lagrangian that allows the construction of the SMEFT expansion, as laid out by other groups, and properties at that point of the Higgs-flare function $\mathcal{F}(h)$ coupling Goldstone and Higgs bosons.
We present a composite two-Higgs-doublet model (2HDM) constructed using dilaton effective field theory. This EFT describes the particle spectrum observed in lattice simulations of a near-conformal SU(3) gauge field theory. A second Higgs doublet is naturally accommodated within the EFT. Using information from numerical lattice studies of the SU(3) gauge theory with eight fundamental (Dirac) fermions, a viable model with moderate parameter tuning may be built. In the relevant portion of parameter space, we show how the model may be matched to a conventional general description of 2HDMs and comment on the role of custodial symmetry (breaking) in the scalar potential. Contributions to the precision electroweak parameter T provide a possible explanation for the recent measurement of the W-boson mass by CDF II.
I will discuss how to use random quantum circuits to sample the average energy---as well as other observables---of a desired Hamiltonian away from the ground state. Then, using those samples, how to estimate the values of observables at low energy by extrapolation.
A simple clustering algorithm based on the euclidean distance among tracks is proposed to find and reconstruct the vertices from where the tracks are emerging. This technique uses the Variational Quantum Eigensolver to find the best combinatorial track to vertex association. The study uses the IBM Quantum Computing simulation framework qiskit to simulate the VQE algorithm. Two vertices have been simulated in order to have the possibility to contrast our results with the actual vertices. Reconstruction efficiencies with respect to the simulation truth are provided as a function of the number of quantum measurements involved in the procedure.
The low-energy regime of QCD is known as the nonperturbative region of QCD because the standard perturbation theory based on the gauge-fixed Lagrangian by the Faddeev-Popov procedure finds a Landau pole at small scales. However, numerical simulations show that the coupling constant, i.e. the one obtained through Taylor's Theorem, remains finite in the infrared. In particular, the development parameter takes values of the order of 0.3. This suggest that some kind of perturbation theory could describe certain behaviours in the infrared. A priori, this seems to be in contradiction with the Landau pole found with the Faddeev-Popov Lagrangian. It turns out that the Faddeev-Popov procedure for fixing the gauge is not well justified for infrared scales (Gribov problem). In fact, it is not known what is the fully justified procedure for fixing the gauge in the infrared. In addition to this fact, numerical simulations on the gluon propagator show that it goes to a finite value in the infrared, acquiring a behavior similar to that of a massive particle. All these observations are taken into account in the Curci-Ferrari model which proposes to add a mass for the gluons in the Lagrangian as a product of the correct gauge fixation. This Lagrangian is infrared save and therefore allows analytical calculations in the infrared. In particular, for the Landau gauge, we show that perturbative results at one and two-loops give a very good description of the propagators and the simulated vertices.
The QCD vacuum has been energetically studied by lattice QCD simulations
with projection methods, such as Abelian projection and center projection.
We propose a new-type projection in the Coulomb gauge, in which gauge configurations are expanded in terms of Faddeev-Popov eigenmodes and only some eigenmodes are kept. With lattice QCD simulations at the quenched level, we apply this projection to the light hadron masses and find that they are reproduced with just a one percent of low-lying eigenmodes. Also, we discuss the results from the viewpoint of the quark model.
Thanks to the recent development of lattice simulation techniques, numerical simulations on an anisotropic system, where the temporal and z directions are compactified while the remaining x and y directions are left infinitely large, have become possible. Such system is understood as an extension of finite-temperature one where only the temporal direction is compactified; namely, the anisotropic system can be regarded as a novel extreme condition of QCD. In this talk, I investigate the phase structures of pure Yang-Mills theory by means of an effective model of Polyakov loops on the anisotropic system, and demonstrate the usefulness of focusing on the novel system comparing to the recent lattice results.
Compact U(1) gauge theory in 3+1 dimensions possesses the confining phase characterized by a linear raise of the potential between particles with opposite electric charges at sufficiently large inter-particle separation. This phenomenon is closely related to the color confinement in non-Abelian gauge theories such as QCD. In QED, the condensation of Abelian monopoles at strong gauge coupling leads to confinement of electric charges because the monopole condensate squeezes the electric flux into a thin electric tube which plays the role of confining string. We investigate how the vacuum structure of the theory is influenced by adding two perfectly-conducting parallel plates associated with the Casimir effect, which predicts that the presence of physical bodies modifies the energy of vacuum fluctuations. Using first-principal numerical simulations in 3+1 dimensional compact U(1) lattice gauge theory, we have found that as the distance between the plates diminishes, the vacuum between the plates undergoes a deconfining transition with the phase transition point shifting towards weaker gauge coupling. The phase diagram in the space of the lattice gauge coupling and the inter-plate distance is obtained.
It is a fundamental question: what is the origin of the glueball masses? In the pure Yang-Mills theory, there is no mass scale in the classical level, while the breaking of scale invariance is induced by quantum effects. This is regarded as the trace anomaly, which is associated with the non-vanishing trace of the energy-momentum tensor (EMT) operator. In this context, the origin of the glueball masses can be attributed to the trace anomaly. Our purpose is to quantify how much the trace anomaly contributes to the glueball masses by using lattice simulations. Once one can have the renormalized EMT operator $T_{\mu\nu}$, the hadron matrix element of $T_{00}$ directly provides the mass of hadron. Therefore, it is natural to consider the mass decomposition in terms of the trace and traceless part of the EMT operator. However, it is hard to construct the renormalized EMT operator on the lattice, where the loss of translational invariance is inevitable due to the discretization of the space-time. To overcome this problem, H. Suzuki proposed that the gradient Yang-Mills flow approach can be utilized to construct the renormalized EMT operator from the flowed fields. In this talk, we directly measure the glueball matrix element of $T_{00}$ that is calculated by the gradient flow method, and then evaluate the contributions of the trace anomaly to the scalar glueball mass.
The Renormalization Group Procedure for Effective Particles (RGPEP) provides the connection between low- and high-energy interactions in QCD through the construction of effective particles [1,2].
The approach reproduces the correct behavior of the coupling constant at high energies (asymptotic freedom) [3] and, at the current level of approximation, the second-order solution of the renormalization group equations yields a Coulomb potential with Breit-Fermi spin couplings, which is corrected by a harmonic oscillator term [4]. These results are obtained assuming that, beyond perturbation theory, gluons get an effective mass.
I present a summary of results obtained with the new method and a regularization procedure which is being tested in different problems.
In the context of a light-front QCD theory for only one heavy flavor, we use the RGPEP to derive the effective potential for 𝑄𝑄¯ and 𝑄𝑄𝑄 that arises at the energy scale at which bound states are formed.
References:
[1] Nonperturbative QCD: A Weak coupling treatment on the light front
K. G. Wilson, T. S. Walhout, A. Harindranath, W.-M. Zhang, R.J. Perry
Phys.Rev.D 49 (1994) 6720-6766
[2] Renormalization of Hamiltonians
S. D. Glazek, K. G. Wilson
Phys.Rev.D 48 (1993) 5863-5872
[3] Asymptotic freedom in the front-form Hamiltonian for quantum chromodynamics of gluons
M. Gómez-Rocha, S. Głazek
Phys.Rev.D 92 (2015) 6, 065005
[4] Renormalized quark–antiquark Hamiltonian induced by a gluon mass ansatz in heavy-flavor QCD
S.D. Glazek, M. Gomez-Rocha, J. More, K. Serafin
Phys.Lett.B 773 (2017) 172-178
The Casimir effect is a remarkable macroscopic feature of QED, while recent lattice studies have also shown its potential nontrivial consequences in QCD.
In light of having a better understanding of the Casimir effect,
it is advantageous to have a self-contained path integral formulation of the phenomenon.
In this talk I will show how the Casimir effect between two uncharged plates in the presence of a chiral medium, modeled with an axion term $\theta \widetilde{F}_{\mu\nu} F^{\mu\nu}$,
can be formulated in terms of the path integral,
and how such a formulation leads to a 3D effective action of the restricted electromagnetic field.
In many physical applications, bound states and/or resonances are observed, which raises the question whether these states are elementary or composite. This talk deals with the calculation of the degree of composition (X) of bound or resonant states. We fist review the “classical” formalism to afford this problem for a bound state in nonrelativistic (NR) Quantum Mechanics (QM). Then, we show how these results can also be obtained by applying Quantum Field Theory (QFT) techniques with the insertion of particle number operators. For the case of resonances we discuss first a quantum mechanical result that shows that resonance states are normalizable to 1 in NR QM in pure potential scattering. This result is also obtained within the treatment based on the particle number operators in QFT, which allows a straightforward extension to coupled-channels. We then discuss the case of energy dependent potentials which give rise to a degree of compositeness less than 1 for bound states. For resonances X is typically complex and we argue about how to get real, meaningful results for them using certain phase transformations in the S matrix. The generation of elementariness in the scattering amplitudes for a given dynamics is treated by introducing CDD poles. For several situations of phenomenological interest, formulas are given that allow evaluating X from the knowledge of the scattering amplitude. Some examples of resonances where these techniques have been applied are presented.
The $\rm{f}_{0}$(980) was observed years ago in $\pi\pi$ scattering experiments. Despite a long history of experimental and theoretical research, the nature of such a short-lived resonance is not understood and there is no consensus on its quark content.
The $\rm{f}_{0}$(980) resonance is measured by ALICE using the $\pi\pi$ decay channel. In this contribution, the multiplicity dependence of transverse-momentum spectra and integrated yields of the $\rm{f}_{0}$(980) produced in pp and p--Pb collisions at $\sqrt{s_{\rm{NN}}} =$ 5.02 TeV are presented. These results are compared with theoretical calculations assuming a molecular structure and a compact tetraquark state. In addition, the nuclear modification factor measured in p--Pb collisions is also presented.
The standard model provides for the existence of hybrid states that contain a gluon in addition to the quark and the antiquark. The $\pi_1(1600)$ and the recently observed $\eta_1(1855)$ are examples of such exotic mesons. In the present work, we study the masses and the two-body decays of the members of the lightest hybrid nonet with quantum numbers $1^{-+}$ using a Lagrangian invariant under the $SU(3)$ flavor symmetry, parity and charge conjugation. We perform a statistical fit to the available experimental and lattice data on the two-body decays of the $\pi_1(1600)$ to arrive at the corresponding coupling constants. Using the parameters so obtained, we analyze the possible decay channels for the hybrid kaons and the isoscalars. We find that the hybrid kaons have to be at least as broad as the $\pi_1(1600)$. The two isoscalar states are the result of a weak mixing between the strange and non-strange isoscalar states. The heavy isoscalar can be identified with the recently observed $\eta_1(1855)$. This state is expected to decay mostly into axial kaons ($K_1(1270)K$). The light isoscalar is expected to be marginally lighter than the $\pi_1(1600)$, and significantly narrower than its heavier sibling.
We will report on recent works featuring the parton distribution functions (DFs) of pion-like systems at experimental scales, following an approach which relies on the assumption that there is an effective charge defining an evolution scheme for DFs that is all-orders exact. Within this framework, strict lower and upper bounds on all Mellin moments of the valence-quark DFs are derived. Furthermore, valence, glue and all flavor sea DFs can be derived from contemporary results from numerical simulations of lattice-regularised QCD. The results from the exploited simulations are seen to obey the derived bounds and become plainly consistent with those obtained from Constinuum Schwinger methods, behaving at large values of the light-front momentum fraction as prescribed by QCD. Finally, we will discuss the extension of the same approach to the proton system.
We compute the QCD static force and potential using gradient flow at next-
to-leading order in the strong coupling. The static force is the spatial derivative of the
static potential: it encodes the QCD interaction at both short and long distances. While
on the one side the static force has the advantage of being free of the O(ΛQCD) renormalon
affecting the static potential when computed in perturbation theory, on the other side its
direct lattice QCD computation suffers from poor convergence. The convergence can be
improved by using gradient flow, where the gauge fields in the operator definition of a given
quantity are replaced by flowed fields at flow time t, which effectively smear the gauge fields
over a distance of order t^(1/2), while they reduce to the QCD fields in the limit t → 0. Based on our next-to-leading order calculation, we explore the properties of the static force for arbitrary values of t, as well as in the t → 0 limit, which may be useful for lattice QCD studies.
In this talk, I discuss our recent determination of nonperturbative matrix elements of heavy quark effective theory (HQET), $\bar{\Lambda}$ and $\mu_{\pi}^2$, which universally parametrize nonperturbative effects on various observables in heavy-light meson systems. In this determination, B meson masses and D meson masses are used as inputs. Using our renormalon subtraction method based on Fourier transform, we subtract not only the u=1/2 renormalon but also the next IR renormalon at u=1 for the first time, from heavy quark pole masses to determine $\bar{\Lambda}$ and $\mu_{\pi}^2$ accurately.
I will discuss the prospects of using femtoscopy in high-energy proton-proton and heavy-ion collisions to learn about the low-energy J/psi-nucleon interaction. Femtoscopy is a technique that makes it possible to obtain spatio-temporal information on particle production sources at the femtometer scale through measurements of two-hadron momentum correlation functions. These correlation functions also provide information on low-energy hadron-hadron forces as final-state effects. In particular, such correlation functions give access to the forward scattering amplitude. One can express the forward amplitude as the product of the J/psi chromopolarizability and the nucleon's average chromoelectric gluon distribution, the latter being relevant to the problem of the origin of the nucleon mass. I will present the results of a recent study using the information on the J/psi-nucleon interaction from lattice QCD simulations to compute J/psi-nucleon correlation functions. The calculated correlation functions show clear sensitivity to the final-state interaction.
Quarkonium production has long been identified as one of the golden signatures of deconfinement in heavy-ion collisions. Recently, the production of J/$\psi$ via (re)generation within the quark-gluon plasma (QGP) or at the phase boundary has been considered a key ingredient for the interpretation of quarkonium measurements in Pb$-$Pb collisions at the Large Hadron Collider (LHC). In addition, the non-prompt J/$\psi$ component, originating from b-hadron decays, allows one to access the interaction of beauty quarks with the QGP in a wide transverse momentum window. Measurements of elliptic flow of charmonia and bottonomia can shed light on the thermalization of charm and beauty quarks inside the QGP. Polarization measurements, besides bringing additional insights into the properties of the QGP, can probe the strong magnetic field generated by the fast motion of the charges of the nuclei as well as the large angular momentum of the medium in non-central events, when performed as a function of the event plane. The study of quarkonium production in smaller systems, such as p$-$Pb and pp, provides a reference for the study of nuclear modifications. Moreover, multiplicity dependent measurements offer a unique opportunity to study both the role of multiparton interactions and the onset of collective effects in small systems.
In this contribution, the latest results on quarkonium production at the LHC will be presented, and the comparison with available theoretical model calculations will be discussed.
Quarks of heavy flavors are useful tool to study quark-gluon plasma created in heavy-ion collisions. Due to their high mass and early production time, heavy quarks experience the entire evolution of the system created in these collisions. Open heavy flavor meson measurements are sensitive to the energy loss in the QGP, while quarkonia are sensitive to the temperature of the QGP as they dissociate because of Debye-like screening of color charges.
This presentation is a summary of the latest heavy flavor studies performed at RHIC. Results from both STAR and PHENIX experiments will be shown, compared to theoretical calculations and the implications discussed.
We present results of nucleon structure studies measured in 2+1 flavor QCD with physical light quarks in large spatial extents of about 10 and 5 fm. Our calculations are performed on 2+1 flavor gauge configurations generated by the PACS Collaboration with the stout-smeared $O(a)$ improved Wilson fermions and Iwasaki gauge action at $\beta$=1.82 corresponding to the lattice spacing of 0.085 fm. In this talk, we mainly focus on nucleon isovector scalar and tensor couplings. Especially, the tensor coupling is known as the 1st Mellin moment of transversity parton distribution and is itself related to the information of quark-EDM.
In this talk, I will review recent progress in lattice calculations of heavy flavor physics. The focus will be on decays of B- and D-mesons and on modern techniques for controlling systematic errors.
The trace anomaly is a quantity of fundamental interest in field theories, which signals whether the underlying theory is conformal. In the context of neutron stars, we propose the trace anomaly for a new measure of the conformality as an alternative to the speed of sound; here we specifically consider the normalized trace anomaly, $1/3 - P/\varepsilon$, with $P$ and $\varepsilon$ being the pressure and energy density, respectively.
By combining the current theoretical and the observational insights, we discuss several interesting features of this quantity:
The trace anomaly inferred from the recent neutron star observations shows the vanishing behavior already around 5-6 times the saturation density. It means that the matter is approximately conformal, which leads to the concept of the strongly-interacting conformal matter inside neutron stars.
We point out a monotonic change in the trace anomaly can lead to a peak in the speed of sound. This is in consonance with the current understanding, and the underlying physics is a rapid liberation of the physical degrees of freedom due to strong interactions of baryons.
We finally conjecture that there is a bound imposed by the positivity of the trace anomaly on the equation of state, and discuss its observational consequences.
I discuss the recent progress in state-of-the art perturbative QCD calculations of the equation of state at large chemical potential. I describe why these calculations that are reliable at asymptotically high densities constrain the equation of state at neutron star densities, and describe how the theoretical calculations can be confronted with multimessenger observations to empirically determine the equation of state. I argue that the properties of the EOS reflect the underlying phase structure and may be used to determine the phase of matter in the cores of neutron stars.
At asymptotically high densities, the neutron-star-matter equation of state (EOS) must approach the EOS of beta-equilibrated QCD matter, as calculated directly within the fundamental QCD theory. This nontrivial constraint at high density, pressure, and chemical potential impacts the inference of the neutron-star-matter EOS at even lower densities. In this talk, I show how this constraint drives the densest matter in the cores of massive neutron stars towards thermodynamic properties consistent with quark matter, even after current astrophysical observations are included in the analysis.
Sp(2N) gauge theories with fermonic matter provide an ideal laboratory to build up phenomenological models for physics beyond the standard model based on novel composite dynamics, where the models include composite Higgs along with partial top compositeness and composite dark matter. Without fermions they also supplement SU(N_c) gauge theories in the large N_c limit. In this talk we report on our recent progress in the numerical studies of Sp(2N) gauge theories discretized on a four-dimensional Euclidean lattice. In particular, we present preliminary results for the low-lying spectra of mesons and chimera baryons in the theories with N=2. We also compute the topological susceptibility for various values of N, which is further extrapolated to the large N limit.
The AdS/CFT correspondence and its generalization to further examples of gauge/gravity duality provide a very useful approach into solving strongly coupled systems. Here, this will be put at work for the strongly coupled sector of Composite Higgs models. We will work out relation between masses of proposed states in Composite Higgs. As a cross check we compare these results to lattice calculations when available for which we find good agreement.
Abstract: The stable hadronic bound states in a hidden new non-Abelian gauge sector provide interesting candidates for strongly-interacting Dark Matter (DM). A particular example are theories in which DM is made up of dark pions which set the DM relic abundance through self-annihilation. One of the simplest realizations is a $Sp(4)$ gauge symmetry with two Dirac fermions. We will discuss its mesonic multiplets for degenerate and non-degenerate fermions and present lattice results for the pseudoscalar and vector channels.
The recent MODE whitepaper, proposes an end-to-end differential pipeline for the optimisation of detector designs directly with respect to the end goal of the experiment, rather than intermediate proxy targets. The TomOpt python package is the first concrete endeavour in attempting to realise such a pipeline, and aims to allow the optimisation of detectors for the purpose of muon tomography with respect to both imaging performance and detector budget. This modular and customisable package is capable of simulating detectors which scan unknown volumes by muon radiography, using cosmic ray muons to infer the density of the material. The full simulation and reconstruction chain is made differentiable and an objective function including the goal of the apparatus as well as its cost and other factors can be specified. The derivatives of such a loss function can be back-propagated to each parameter of the detectors, which can be updated via gradient descent until an optimal configuration is reached. Additionally, graph neural networks are shown to be applicable to muon-tomography, both to improve volume inference and to help guide detector optimisation.
MODE et al. (2022) Toward the End-to-End Optimization of Particle Physics Instruments with Differentiable Programming: a White Paper, arXiv:2203.13818 [physics.ins-det]
Nuclear and particle physics research relies on accurate models which generate samples from conditional densities. An implicit quantile network (IQN) is a simple neural network-based machine learning model that has the ability to generate accurate samples from conditional, joint probability density functions. In this talk, we illustrate the capabilities of IQNs for simple generative tasks, as well as for the physics context of jet simulations. Specifically, we emulate folding, a stochastic process where a jet is smeared by a response function, such as interactions with a detector.
The ability to accurately observe two or more particles within a very small time window has always been a great challenge in modern physics, while holding great potential. It opens the possibility for correlation experiments, as for example the ground-breaking Hanbury Brown-Twiss experiment, that can lead to physical insights. For low-energy electrons, one possibility is to use a micro-channel plate with subsequent delay-lines for the readout of the incident particles. With such a detector, the spatial and temporal coordinates of more than one particle can be fully reconstructed outside a certain dead-radius. For close-by events, the determination of the individual positions of the particles using a delay-line detector requires elaborated peak finding algorithms. While classical methods work well for single hits, they fail at identifying and reconstructing multiple hits when they get very close. In order to increase the resolution for close double hits, we train a recurrent neural network to recover the peak positions. We show that the temporal and spatial resolution for double hits is greatly improved with the application of deep neural networks compared to previously used methods.
The four types of maximally nontrivial calorons in SU(2)-QCD have characteristic spatial distribution of Polyakov loops. We describe a classical geometric model of an SU(2)-field with finite, stable solitonic solutions with the same structure as these four types of calorons. These solitons are characterised by two topological quantum numbers which can be compared with electric charge and spin. Two
additional Goldstone bosons we relate to the properties of photons.
The quark confinement in QCD is achieved by concentration of the chromoelectric field between the quark-antiquark pair into a flux tube, which gives rise to a linear quark-antiquark potential. We study the structure of the flux tube created by a static quark-antiquark pair in the pure gauge SU(3) theory, using lattice Monte-Carlo simulations. We calculate the spatial distribution of all three components of the chromoelectric field and perform the "zero curl subtraction" procedure to obtain the nonperturbative part of the longitudinal component of the field, which we identify as the part responsible for the formation of the flux tube. Taking the spatial derivatives of the obtained field allows us to extract the electric charge and magnetic current densities in the flux tube. The behavior of these observables under smearing and with respect to continuum scaling is investigated. Finally, we briefly discuss the role of magnetic currents in the formation of the string tension.
The spectrum of QCD is expected to contain, besides bound states of quarks, also bound states of gluons. These glueballs can mix with other states that have the same quantum number. For pure Yang-Mills theory, on the other hand, glueballs are the only physical degrees of freedom which makes the picture much clearer. Using state-of-the-art, parameter-free solutions for the propagators and vertices from Dyson-Schwinger equations as input, I present part of the glueball spectrum as calculated from bound state equations. The good agreement of the results with lattice results paves the way for studying the mixing with conventional mesons in the future.
We discuss the status of both conventional and unconventional mesons between 1 and 2 GeV by using hadronic models that describe their masses, strong, and radiative decays. Various conventional quark-antiquark states are considered: some of them, such as the tensor mesons with $J^{PC}=2^{++}$ and mesons with $J^{PC}=3^{--}$, form well established nonets, while other, such as the axial-tensor mesons with $J^{PC}=2^{--}$, are poorly known and still need experimental detection. Then, we also present latest results for some non-conventional candidates, such as the case of hybrid mesons with $J^{PC}=1^{-+}$ or the tensor glueball.
The quark-gluon vertex is one of the basic building blocks of the strong interaction. It is an essential ingredient in functional approaches to nonperturbative quantum chromodynamics (QCD). In the literature, many studies of hadron phenomenology in the Schwinger-Dyson Equation framework have been carried out using the rainbow-ladder truncation, where the quark-gluon vertex is approximated by its tree-level structure, multiplied by an effective coupling which is assumed to depend only on the gluon momentum. While this approach has been successful in describing a range of properties of pseudoscalar and vector mesons, it has failed to provide a satisfactory description of other quantities including scalar and axial-vector mesons and the chiral transition temperature. In this presentation we will summarise the latest developments in quark-gluon vertex structure and its implications in hadron physics.
We present a calculation of the heavy quark transport coefficients in a quark-gluon plasma under the presence of a strong external magnetic field, within the Lowest Landau Level (LLL) approximation. In particular, we apply the Hard Thermal Loop (HTL) technique for the resummed effective gluon propagator, generalized for a hot and magnetized medium. Using the derived effective HTL gluon propagator and the LLL quark propagator we analytically derive the full results for the longitudinal and transverse momentum diffusion coefficients as well as the energy losses for charm and bottom quarks beyond the static limit. We also show numerical results for these coefficients in two special cases where the heavy quark is moving either parallel or perpendicular to the external magnetic field.
Electromagnetic radiation from the quark-gluon plasma (QGP) is an important observable to be carefully considered in heavy ion collision experiments. At leading order in the electromagnetic coupling and all orders in the strong coupling, the photon and dilepton emission rates can both be determined from the QCD vector channel spectral function. In this talk, I will provide a status update from perturbation theory and lattice simulations. The resummed next-to-leading order (NLO) result has recently been decomposed into transverse and longitudinal components, and extended to non-zero baryon chemical potential $\mu_{\rm B}$. I will discuss how the NLO spectral function holds up to scrutiny from another observable, the Euclidean correlator for the difference between polarisation components, judged against continuum-extrapolated lattice data (at $\mu_{\rm B}=0$). It turns out that the presence of $\mu_{\rm B}$ modifies not only the quark distribution in the QGP, but also the thermal masses that control the necessary screening effects: the outcome for emission rates depends on the photon's invariant mass. Ultimately, these rates can be embedded in hydrodynamical simulations of heavy ion collisions and I will report on new predictions of the dilepton yield at RHIC and LHC energies, as well as low-energy experiments that probe QGPs with net baryon content.
The High Acceptance DiElectron Spectrometer (HADES) is a versatile detector with particular focus on dielectron measurements in pion, proton, deuteron and (heavy-) ion-induced reactions using proton or nuclei targets in the SIS-18 energy range (1-2 GeV/nucleon). Its excellent particle identification capabilities also allow for the investigation of hadronic observables.
The excess of dileptons above the contributions from initial state processes and late meson decays serve as messengers of the dense medium created in heavy-ion collisions and reveal the thermal properties and the lifetime of the medium but also give insight into meson properties at high densities. A high statistics sample of Ag+Ag collisions ($4.5$ billion events for $0 - 40 \%$ centrality) at $\sqrt{s_{NN}} = 2.55 \, GeV$ with improved electron detection efficiency and background suppression has been analyzed and is presented as a function of centrality and pair-momentum with a signal up to the phi meson mass region. The obtained dilepton spectra show a strong excess radiation and suggest a substantial modification of the mesons.
In order to study the electromagnetic and hadronic couplings of baryonic resonances to the $\rho-N$ final state, which is particularly important for the understanding of the emissivity of hot and dense nuclear matter due to the important role of intermediary vector mesons in dilepton emission, HADES has initiated a dedicated pion-nucleon program in order to investigate the second resonance region. Baryon-meson couplings and the validity of the vector dominance model for baryon transitions were investigated, the importance of the latter clearly being underlined. A first glimpse on new results from the recent p+p beamtime at $4.5 \, GeV$ beam energy will also be presented.
We present a systematic investigation of the possible locations for the special point (SP), a unique feature of hybrid neutron stars in the mass-radius. The study is performed within the two-phase approach where the high-density (quark matter) phase is described by the constant-sound-speed (CSS) equation of state (EoS) and the nuclear matter phase around saturation density is varied from very soft (APR) to stiff (DD2 with excluded nucleon volume). Different construction schemes for the deconfinement transition are applied: Maxwell construction, mixed phase construction and parabolic interpolation. We demonstrate for the first time that the SP is invariant not only against changing the nuclear matter EoS, but also against variation of the construction schemes for the phase transition. Since the SP serves as a proxy for the maximum mass and accessible radii of massive hybrid stars, we draw conclusions for the limiting masses and radii of hybrid neutron stars.
We study the impact of asymmetric fermionic and bosonic dark matter on neutron star properties, including tidal deformability, maximum masses, radii, etc. The conditions at which dark matter particles tend to condensate in the core of the star or create an extended halo are presented. We show that dark matter condensed in a core leads to a decrease of the total gravitational mass and tidal deformability compared to a pure baryonic star, which we will perceive as an effective softening of the equation of state. On the other hand, the presence of a dark matter halo increases those observable quantities. Thus, observational data on compact stars could be affected by an accumulated dark matter and, consequently, constraints we put on strongly interacting matter at high densities. We will discuss how the ongoing and future X-ray, radio and GW observations could shed light on dark matter admixed compact stars and put multi-messenger constraints on its effect.
More than 20 years ago, Glendenning et al. (1995) proposed the existence of stable white dwarfs with a core of strange quark matter. More recently, by studying radial modes, Alford et al. (2017) concluded that those objects are unstable. We investigate again the stability of these objects by looking at their radial oscillations, and we assume that there is no phase transition between hadronic and quark matter at the strange core interface, following the formalism developed by Pereira et al. (2018) and Di Clemente et al. (2020). Our analysis shows that if the star is not strongly perturbed and ordinary matter cannot transform into strange quark matter, this type of objects are indeed stable. On the other hand, ordinary matter can be transformed into strange quark matter if the star undergoes a violent process, as in the early stages of a supernova, causing the system to become unstable (as described by Alford et al. (2017)) and collapse into a strange quark star. In this way, km-sized objects with subsolar masses can be produced.
Di Clemente, Drago, Pagliara and Char, in preparation.
Glendenning, Kettner, Weber, PRL 74 (1995) 3519; ApJ 450 (1995) 253
Alford, Harris, Sachdeva, ApJ 847 (2017) 109
Pereira, Flores, Lugones, ApJ 860 (2018) 12
Di Clemente, Mannarelli, Tonelli, PRD 101 (2020) 103003
In real-world QCD and its large-N generalization, it is not clear how confinement/deconfinement transition can be defined in terms of symmetry. Dynamical fundamental quarks spoil the center symmetry, and finite quark mass spoils the chiral symmetry. It is widely believed there is no phase transition in the literal sense. However, progress in holography and QCD-like theories suggest the existence of phase transitions --- not just one, but actually two. Analytic calculations in some theories suggest the Polyakov loop plays an important role, although the symmetry behind it was not identified.
In this talk, I show that the Polyakov loop is directly connected to gauge symmetry. The Polyakov loop can be defined in the operator formalism as well, and it captures the symmetry of the quantum states dominating thermodynamics. In the large-N limit, two phase transitions correspond to the transition from the completely-confined phase to the partially-deconfined phase, and the other transition from the partially-deconfined phase to the completely-deconfined phase. In fact, this can be understood almost trivially if one notices a connection between Bose-Einstein condensation and color confinement at large N. Indeed, Feynman made a similar observation in 1953! We suggest this story generalizes to SU(3).
The gauge/gravity duality can be used to constrain QCD at intermediate densities and temperatures, where first-principles methods are not available. I will give an overview on recent results from the V-QCD model in this region, including predictions for the phase diagram, deconfinement transition, equation of state, and transport of dense QCD matter. If time permits, I will also discuss applications to neutron stars and binary neutron star mergers.
We compare the behavior of zero-modes of the overlap Dirac operator measured on the finite temperature 2+1 flavor lattice QCD configurations, generated with domain wall fermion discreitzation, to the local Polyakov Loop in the temperature range 1.1-1.2T_c, T_c being the pseudo-critical temperature. We show how the position of the zero-modes are anti-correlated to the local value of the Polyakov Loop.
Meissner effect for the chromoelectric field is the property of the non-perturbative QCD vacuum postulated to describe color confinement. We follow London's macroscopic theory of the Meissner effect for the magnetic field in superconductors and obtain the dual Meissner effect by fixing the phenomenological color gluon current assumed relevant at strong coupling. Its non-Abelian piece is simply related with the chromomagnetic current of the QCD Bianchi identity. It is tempting to associate the expected macroscopic dual color superconductivity with the observed almost perfect fluidity in droplets of the strongly interacting quark-gluon plasma.
Quantum Chromodynamics permits the formation of charge-parity violating domains inside the medium produced in heavy-ion collisions resulting in an imbalanced quark chirality. With the precense of a strong magnetic field (as strong as $10^{15}$ T) produced by the spectator protons in off-central heavy-ion collisions, this would lead to an electric-charge separation along the direction of the magnetic field known as the Chiral Magnetic Effect (CME). Experimental searches commonly utilise strategies involving charge-dependent correlations to measure the charge separation, while charge-dependent correlators are dominated by large background proportional to the elliptic flow $v_{2}$.
In this talk, I will discuss the latest studies at LHC energies and present a systematic study of the correlators used experimentally to probe CME using the Anomalous Viscous Fluid Dynamics (AVFD) model in Pb-Pb and Xe-Xe collisions at $\sqrt{s_{NN}}=5.02$ TeV and $\sqrt{s_{NN}}=5.44$ TeV, respectively. The results from AVFD suggest that Xe-Xe collisions are consistent with a background-only scenario and a significant non-zero value of axial current density (imbalanced quark chirality) is required to match the measurements in Pb-Pb collisions.
It is known that 1+1 dimensional real scalar models with a negative mass squared have a soliton solution called the kink. We analyze the distribution of the energy-momentum tensor around the kink by incorporating the quantum correction up to leading order. The Fourier transform of the distribution corresponds to the gravitational form factors. We employ the collective coordinate method which deals with the soliton's coordinate as a dynamical variable. The zero mode that gives rise to the infrared divergence is eliminated in this method. The ultraviolet divergences in the quantum correction are removed by the vacuum subtraction with the prescription called the mode-number cutoff and the mass renormalization. We obtain the result consistent with the energy-momentum conservation. The spatial integral of the energy density agrees with the known result on the total energy of the soliton.
We report novel lattice QCD results for the position-space gluon propagator from quenched lattice-QCD simulations. Using standard Wilson action, we have computed the gluon propagator in position space with a detailed treatment of discretization errors.
We discuss on the usefulness of the long-distance behavior of gluon propagator for constraining the deep infrared running of the gluon propagator.
In addition, we will show results for the three-gluon vertex that support the
gluon-mass generation mechanism based in the existence of massless poles, longitudinaly coupled to the gluon momenta, in the vertices of QCD.
The photon propagator for the pure gauge theory is revisited using large lattices. For the confined case we show that it has an associated linearly growing potential, it has a mass gap, that is related to the presence of monopoles, and its spectral function violates positivity. In the deconfined phase, our simulations suggest that a free field theory is recovered in the thermodynamic limit.
A metastable phase has important physical implications, since it may form vacuum bubbles detectable experimentally. It is well known that, due to spontaneous chiral symmetry breaking, there are two, or more, different QCD vacua. In the chiral limit, in the true vacuum, the pseudoscalar ground states are Goldstone bosons. The chiral invariant vacuum (at the top of the "Mexican hat") is an unstable vacuum decays through an infinite number of scalar and pseudoscalar tachyons. Besides, QCD vacuum replicas, an infinite tower of excited vacuum solutions, have been predicted in the Coulomb gauge. It remained to show whether the QCD replicas are metastable or unstable. We study the spectrum of quark-antiquark systems in the first excited QCD replicas. The mass gap equation for the vacua and the Salpeter-RPA equation for the mesons are solved for a simple chiral invariant and confining model of the Coulomb gauge. We find no tachyons, thus showing the QCD replicas in our approach is indeed metastable. Moreover the energy spectra of the mesonic quark-antiquark systems in the first replicas are close to the one of the true vacuum.
Observation of the scalar glueball, evidence for the tensor glueball, how to search for the pseudoscalar glueball
The scalar glueball is observed in a coupled-channel analysis of the $S$-wave amplitude from BESIII data on radiative $J/\psi$ decays and further data. Ten scalar isoscalar resonances were required to fit the data. Five of them were interpreted as mainly singlet, five as mainly octet resonances in SU(3). The yield of resonances showed a striking peak with properties expected from a scalar glueball:
$\bullet$ $G_0(1865)$ is produced abundantly in radiative $J/\psi$ decays above a very low background. Its mass is $1\sigma$ compatible with the mass calculated in unquenched lattice QCD and the yield is $1.6\sigma$ compatible with the yield calculated in lattice QCD
$\bullet$ The decay analysis of the scalar isoscalar mesons shows that the assignment of mesons to mainly-octet and mainly-singlet states is correct. Even the production of mainly-octet scalar mesons - which should be forbidden in radiative $J/\psi$ decays - peaks at 1865 MeV.
$\bullet$ The decay analysis requires a small glueball content in the flavor wave
function of several scalar resonances.
$\bullet$ The glueball content as a function of the mass shows a peak compatible with the peak in the yield of scalar isoscalar mesons. The sum of the fractional glueball contributions is compatible with one.
$\bullet$ In the reaction $B_s\to J/\psi + K^+K^-$ reported by the LHCb collaboration, a primary $s\bar s$ couples to mesons having a strong coupling to $K^+K^-$.Two peaks in the $K^+K^-$ mass spectrum are seen due to $\phi(1020)$ and $f_2'(1525)$ , but there is no sign for the $f_0(1710)$ which is known to couple strongly to $K\bar K$. High-mass scalar mesons are strongly produced by two initial-state gluons but not by an $s\bar s$ pair in the initial state. They must have sizable glueball fractions!
The $D$ wave amplitude in the BESIII data on radiative $J/\psi$ decays reveales a high-mass structure which can be described by a single Breit-Wigner or by the sum of three $\phi\phi$ resonances interpreted as tensor glueballs a long time ago. The structure - and further tensor resonances observed in radiative $J/\psi$ decays - are tentatively interpreted as tensor glueball.
In $J/\psi$ decays into $\gamma\pi^0\eta\eta'$ several resonances are reported. The possibility is discussed that the pseudoscalar glueball might be hidden in these data.
The excitation spectrum of light mesons; which are composed of up, down, and strange quarks; allows us to study QCD at low energies. While the non-strange light-meson spectrum is al- ready mapped out rather well, many predicted strange mesons have not yet been observed experimentally and many potentially observed states still need further confirmation. Hence, the strange-meson spectrum still holds many surprises that need to be discovered. The COMPASS experiment at CERN has studied so far mainly non-strange mesons of the aJ and πJ families with high precision, using the dominating π− component of the beam. Using the smaller K− component allows us to investigate also the spectrum of strange mesons. The flagship channel is the K−π−π+ final state, for which COMPASS has acquired the so-far world’s largest data set. Based on this data set, we performed a partial-wave analysis in order to disentangle the produced mesons by their spin-parity quantum numbers. In this talk, we will focus on recent results from this analysis of COMPASS data and we will give prospects for a high-precision measurement of the strange-meson spectrum at AMBER – a new QCD facility at CERN.
We present results on the in-medium interactions of static quark anti-quark pairs using realistic 2+1 HISQ flavor lattice QCD. Focus is put on the extraction of spectral information from Wilson line correlators in Coulomb gauge using four complementary methods. Our results indicate that on HISQ lattices, the position of the dominant spectral peak associated with the real-part of the interquark potential remains unaffected by temperature. This is in contrast to prior work in quenched QCD and we present follow up comparisons to newly generated quenched ensembles.
We present work [1], in which we extend the publicly available quantumfdtd code. It was originally intended for solving the time-independent three-dimensional Schrödinger equation via finite-difference time-domain (fdtd) method and extracting the ground, first and second excited states. We extend it to (a) include the case of the relativistic Schrödinger equation and (b) add two optimized FFT-based kinetic energy terms for the non-relativistic case. All the three new kinetic terms (the two non-relativistic and the relativistic one) are computed using Fast Fourier Transform (FFT). We release the resulting code as version 3 of quantumfdtd. Finally, the original code now supports arbitrary external file-based potentials and the option to project out distinct parity eigenstates from the solutions.
Most quark models used for phenomenological descriptions of QCD bound states are described by the three-dimensional Schrödinger equation with different potentials. In particular, these models have successfully describe below-threshold charmonium production and bottomonium spectra and have helped to establish confidence in QCD as the first-principles description of hadronic matter [2–4]. Non-relativistic effective field theory methods have been used for a first-principles approach to potential-based non-relativistic QCD (pNRQCD) [5,6]. In order to describe quarkonium evolution in the quark-gluon plasma, these potential models have been extended to finite temperature [7–9] and non-equilibrium [10–14]. In the last case, the potentials are no longer real-valued or spherically symmetric. In the full non-equilibrium case, a full three-dimensional solver, like the one developed in this work, is necessary.
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We generalize a complex heavy-quark potential model from an isotropic QCD plasma to an anisotropic one by replacing the Debye mass $m_D$ with an anisotropic screening mass depending on the quark pair alignment with respect to the direction of anisotropy.
Such an angle-dependent mass is determined by matching the perturbative contributions in the potential model to the exact result obtained in the Hard-Thermal-Loop resummed perturbation theory. An advantage of the resulting potential model is that its angular dependence can be effectively described by using a set of angle-averaged screening masses as proposed in our previous work. Consequently, one could solve a one-dimensional Schrodinger equation with a potential model built by changing the anisotropic screening masses into the corresponding angle-averaged ones, and reproduce the full three-dimensional results for the binding energies and decay widths of low-lying quarkonium bound states to very high accuracy. Finally, turning to dynamics, we demonstrate that the one-dimensional effective potential can accurately describe the time evolution of the vacuum overlaps obtained using the full three-dimensional anisotropic potential. This includes the splitting of different p-wave polarizations.
We study the chiral condensate for 2+1 flavor QCD with physical quarks within a non-interacting Hadron Resonance Gas (HRG) model. By including the latest information on the mass variation of the hadrons with respect to the light quark mass, from lattice QCD and chiral perturbation theory, we show that it is possible to quite accurately account for the chiral crossover transition even within a conventional HRG model. We have calculated a pseudo-critical temperature $T_c=161.2 \pm 1.6$ MeV and the curvature of crossover curve $\kappa_2=0.0203(7)$. These are in very good agreement with the latest continuum extrapolated results obtained from lattice QCD studies. We also discuss the limitations of extending such calculations toward the chiral limit. Furthermore, we study the effects of non-resonant hadron interactions within the HRG model and its consequences for the chiral transition in the regime of dense baryonic matter where lattice QCD results are not currently available.
Experimental searches for neutrinoless double-beta decay aim to determine whether the neutrinos are Dirac or Majorana fermions. Interpreting double-beta half-lives or experimental exclusions in terms of neutrino physics requires knowledge of the nuclear matrix elements, which are currently estimated from various nuclear models and carry a large model uncertainty. This talk will present preliminary results from a first-principles lattice QCD calculation of the short-distance (from a heavy intermediate Majorana neutrino) and long-distance (from a light Majorana neutrino) nuclear matrix elements for the simple nn → ppee transition at an artificially heavy quark mass, where the dineutron is a bound nucleus. Such results can provide input for nuclear EFTs that can be extrapolated to nuclei of interest to reduce model uncertainties.
Motivated by axion physics, the topological susceptibility at high temperature was calculated by several lattice groups. A comparison with the semi-classical calculation at high temperature is meaningful and the details of the instanton calculation is reviewed. The correct over-all factor in MSbar and high precision parametrization of the temperature dependence is presented.
We compute the topological susceptibility of high temperature QCD with 2+1 physical mass quarks using the multicanonical approach and the spectral projector estimate of the topological charge. This approach presents reduced lattice artifacts with respect to the standard gluonic one, and makes it possible to perform a reliable continuum extrapolation.
Charge radii of the light nuclei depend on the charge distributions of the proton and the neutron and on the nuclear structure --- the way how nucleons are distributed inside the nucleus. We present a high-accuracy calculation of the nuclear structure for A=2,3,4 nuclei using the latest two- and three-nucleon forces and charge density operators derived up through the fifth order in the chiral effective field theory. We predict the structure radii of the deuteron, the alpha-particle and the isoscalar combination of 3H and 3He, and perform a comprehensive analysis of various sources of uncertainties. Using the predicted value of the deuteron structure radius together with very precise spectroscopic data for the deuteron-proton charge radius difference we extract the neutron charge radius. Combining predicted alpha-particle structure radius with the precise 4He charge radius measurement we extract the charge radius of the proton. Finally, using the predicted isoscalar combination of the 3H and 3He structure radii and the preliminary experimental data for the 3He charge radius we estimate the charge radius of triton.
There is presently no consensus on how the $\phi$ meson mass and width will change once it is put in a dense environment such as nuclear matter. While many theoretical works exist, connecting them with experimental measurements remains non-trivial task, as the $\phi$ meson in nuclear matter is usually produced in relatively high-energy pA reactions, which are generally non-equilibrium processes. In this presentation I will report on an ongoing project [1], attempting to simulate pA reactions in which the $\phi$ meson is produced in nuclei, making use of a transport approach [2]. Results of simulations of 12 GeV/30 GeV p+C and p+Cu reactions will be presented and comparisons between obtained dilepton spectra and experimental data of the E325 experiment at KEK [3] will be made. Furthermore, predictions for the ongoing J-PARC E16 experiment [4] for both dilepton and $K^+K^-$ spectra will be given and discussed.
[1] P. Gubler and E. Bratkovskaya, in progress.
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[4] S. Ashikaga et al., (J-PARC E16 Collaboration), JPS Conf. Proc. 26, 024005 (2019).
With the detection of compact binary coalescences and their
electromagnetic counterparts by gravitational-wave detectors, a new
era of multi-messenger astronomy has begun. In this talk, I will
describe how GW170817, our first example in this new class, is being
used to constrain the unknown equation of state of cold supranuclear
matter, and to measure the Hubble constant. I will then discuss how
current ground based optical surveys and dedicated follow-up systems
are being used to identify more of these, and how we are developing
models to test what we find. We will close with near-term prospects
for the field.
Thermal production of sexaquarks are calculated in different Statistical Models.
Sexaquarks are a hypothetical low mass, small radius uuddss dibaryon which has been proposed recently and especially as a candidate for Dark Matter [1,2]. The low mass region below 2 GeV escapes upper limits set
from experiments which have searched for the unstable, higher mass H-dibaryon and did not find it [1].Depending on its mass, such state may be absolutely stable or almost stable with decay rate of the order of the lifetime
of the Universe therefore making it a possible Dark Matter candidate [2].Even though not everyone agrees [3] its possible cosmological implications as DM candidate cannot be excluded and it has been recently searched in the BaBar experiment [4].
The assumption of a light Sexaquark has been shown to be consistent with observations of neutron stars [5] and the Bose Einstein Condensate of light Sexaquarks has been discussed as a mechanism that could induce quark deconfindement in the core of neutron stars [6].
S production in heavy ion collisions is expected to be much more favorable than in the only experimental search to date, $\Upsilon \rightarrow 𝑆\bar{\Lambda} \bar{\Lambda}$ [4], which is severely suppressed by requiring a low multiplicity exclusive final state [1]. By contrast, parton coalescence and/or thermal production give much larger rates in heavy ion collisions [1,8].
We use a model which has very successfully described hadron and nuclei production in nucleus-nucleus collisions at the LHC [7], in order to estimate the thermal production rate of Sexaquarks with characteristics such as discussed previously rendering them DM candidates.
We show new results on the variation of the Sexaquark production rates with mass, radius and temperature and chemical potentials assumed and their ratio to hadrons and nuclei and discuss the consequences.
These estimates are important for future experimental searches and enrich theoretical estimates in the multiquark sector.
The microscopic production rates of exotic states like $X(3872)$ [9] and Pc(4312), Pc(4440), Pc(4457) [10] are calculated
in pp collisions at $\sqrt(s)$ 7 and 13 TeV within MC PACIAE+DCPC model for three different scenarios:
i.e.pentaquark state, nucleus-like state and molecular state.
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[9] H.G.Xu et al EPJC 81 (2021) 784
[10] C.H. Chen et al arXiv:2111.03241, Accepted by PRD
Evidence has emerged recently in large N gauge theories that a `partially-deconfined’ phase can appear between confined and deconfined phases. In this phase, only a subset of colours deconfine. The centre symmetry is spontaneously broken in the partially-deconfined phase, raising the question of whether an order parameter exists that can also distinguish it from the completely-deconfined phase. We present two examples in gauge theories of global symmetries that are spontaneously broken in the confined phase and preserved in the deconfined phase, and we show that this symmetry is spontaneously broken in the partially-deconfined phase. Consequently, in these theories the transition from complete to partial deconfinement is accompanied by the spontaneous breaking of a global symmetry. The two examples are CP symmetry in $\mathcal{N}=1$ super-Yang-Mills with a massive gluino and theta-angle $\theta=\pi$, and chiral symmetry in a strongly-coupled lattice gauge theory. For $\mathcal{N}=1$ SYM we also present numerical evidence that the same phenomenon occurs at finite $N \geq 30$. We thus conjecture that global symmetries may provide order parameters to distinguish completely and partially deconfined phases generically, including at finite $N$.
We study graviton-graviton scattering in partial-wave amplitudes after unitarizing their Born terms. In order to apply S-matrix techniques, based on unitarity and analyticity, we introduce an S-matrix associated to this resummation that is free of infrared divergences. This is achieved by removing the diverging phase factor calculated by Weinberg that multiplies the S matrix, and that stems from the
virtual infrared gravitons. A scalar graviton-graviton resonance with vacuum quantum numbers is obtained as a pole in the nonperturbative S-wave amplitude, which we call the graviball. Its resonant effects along the physical real-s axis may peak at values substantially lower than the UV cutoff squared of the theory. For some scenarios, this phenomenon could have phenomenological consequences
at relatively low-energy scales, similarly to the σ resonance in QCD. These techniques are also applied to study the gravitational scattering of two massive scalars and its resulting pole content.