2023 Annual NPACT Meeting

7 Aug 2023, 12:00 → 8 Aug 2023, 17:00 Europe/Oslo

Room 359 (UiB)

Monday, 7 August

12:00 Lunch and welcome

1 Searches for gravitational waves

Speaker: Alex Nielsen (University of Stavanger)

NPACT2023_Nielsen.pdf

2 Gravitational lensing

Speaker: Ben Normann (NTNU)

NPACT2023_Normann.pdf

3 Using Feynman diagrams to compute the influence of additional fields on gravitational wave sources

One way of modifying gravity is by adding additional fields to the action. In this talk, I will demonstrate how to compute the effect of such additional fields on a binary's gravitational potential. As will be discussed, the gravitational waveform generated by a compact binary is highly dependent on the potential, and thus such extensions of gravity may be detectable by gravitational waves.

The talk might be modified to focus more on LIGO activities if relevant.

Speaker: Vegard Undheim (University of Stavanger)

NPACT2023_Undheim.pdf

14:30 Coffee break

4 QCD in the cores of neutron stars

Rapid advancement in neutron-star observations allows unprecedented empirical access to cold, ultra-dense QCD matter, complementing collider experiments. The combination of these observations with theoretical calculations reveals previously inaccessible features of the equation of state and the phase diagram of QCD. In this talk, I demonstrate how perturbative-QCD calculations at asymptotically high densities robustly constrain the equation of state at neutron-star densities using a new method solely based on causality and stability. I confront these calculations with neutron-star observations in a Gaussian-process-based Bayesian framework and demonstrate that the perturbative-QCD calculations offer significant and nontrivial information, going beyond that which is obtainable from current observations. The main effect of the QCD input is to soften the equation of state at high densities, supporting the hypothesis that most massive neutron stars have quark matter cores.

Speaker: Oleg Komoltsev (University of Stavanger)

NPACT2023_Komoltsev.pdf

Tuesday, 8 August

5 GAMBIT-light

I will introduce GAMBIT-light, a lightweight and user-friendly version of the GAMBIT framework, intended as a discipline-agnostic tool for computationally expensive parameter estimation and model comparison problems.

Speaker: Anders Kvellestad (University of Oslo)

NPACT2023_Kvellestad.pdf

6 Physics Learning Using Machines and Bayesian INference (PLUMBIN')

In this talk we will describe the PLUMBIN' project which has recently been funded by the Research Council of Norway. PLUMBIN' is a cross-disciplinary project with collaboration between high-energy theoretical physics and statistics, focused on developing modern tools for new physics searches. We will put some emphasis on describing the sort of problems that PLUMBIN' sets out to solve, rather than the solutions (which still need some work).

Speaker: Are Raklev (University of Oslo)

7 Universality of jet energy loss in the quark-gluon plasma using Bayesian inference

Data from a wide range of jet observables measured in heavy ion collisions provide a comprehensive picture of jet modification by the resulting quark-gluon plasma. In this way, the medium-modified jets act as a perturbative probe that allows us to infer the properties of the medium. However, their interpretation is often limited by the assumptions of specific quenching models, and it remains a challenge to establish model-independent statements about the universality of different jet quenching observables.

In this work, we address this issue by proposing a treatment that is agnostic to the details of the jet-medium interactions and relies only on the universality of quark and gluon quenching in different jet observables. We use Bayesian inference to constrain the parameterisation of the energy loss of quark- and gluon-initiated jets in a data-driven manner. This constraint is primarily performed using the inclusive jet pT spectrum, for which the quark/gluon fraction varies across rapidity. We then predict the observed jet asymmetry in di-jet and boson-jet measurements, providing evidence for the universality of quenching effects.

Furthermore, we examine the extracted Casimir scaling of jet quenching and the role of resolution effects in constraining the early, perturbative jet evolution using these data-driven methods. This study provides a new perspective on the universality of jet quenching in heavy ion collisions, free from the assumptions of specific models.

Speaker: Alexandre Falçao (University of Bergen)

NPACT2023_Falcao.pdf

8 The ultraviolet myth

We have all heard how classical physics predicts an infinite amount of ultraviolet radiation from a black-body and how Planck solved this by quantizing the electromagnetic radiation.
This, however, is a myth, nobody at the time was worried about any ultraviolet catastrophe, the term was not even coined until 11 years after Planck. So what did Planck do and why? That will be the topic of this presentation.

Speaker: Nils-Erik Bomark (University of Agder)

NPACT2023_Bomark.pdf

12:00 Lunch

9 N-PACT discussion

14:00 Coffee break

10 Instabilities in Anisotropic Non-Abelian gauge fields

Anisotropies in the context of heavy ion collisions are well known. The system of gluon fields generated during the heavy-ion collisions are unstable and the nature of these instabilities are not well known. To understand them better, we study the behaviour of different modes with various combinations of Abelian and non-Abelian electric and magnetic fields with small fluctuations around the background fields which obey the linearized Yang-Mills equations.

Speaker: Divyarani Chandrababu Geetha (University of Stavanger)

11 A variational approach to discretised initial value problems

In this talk I present recent work on numerically determining the classical trajectories of initial value problems from a variational principle that implements manifest time translational symmetry.

Speaker: Alexander Rothkopf (University of Stavanger)

NPACT2023_Rothkopf.pdf

12 The Mathematics of Higher Symmetries

Lately the theoretical physics community has seen a keen interest in the notion of higher symmetries, both from a global and local perspective. Understanding this mathematically can be key for doing good physics. Just like general relativity requires differential geometry, and ordinary gauge theory is described using the language of vector bundles, higher symmetries are modelled mathematically using things like gerbes, higher groups, and so on. I will give a brief introduction to these objects, and give some examples both from particle physics, gravity and string theory.

Speaker: Eirik Eik Svanes (University of Stavanger)

NPACT2023_Svanes.pdf