32nd Nordic Network Meeting on "Strings, Fields and Branes"

4 Dec 2023, 11:25 → 6 Dec 2023, 17:15 Europe/Oslo

E-102 (Kjølv Egelands hus)

Eirik Eik Svanes (University of Stavanger), Paul de Medeiros (University of Stavanger), Sigbjørn Hervik (University of Stavanger)

The 32nd Nordic Network Meeting on "Strings, Fields and Branes" is organised by the Department of Mathematics and Physics at the University of Stavanger, and will be held 4-6th of December 2023.

For the first time in Stavanger, this series of meetings is intended to provide opportunities for PhD students and researchers in String Theory and related topics working within the Nordic community to interact and exchange ideas. It also aims to put students and young researchers in contact with the forefront of current research in the field, through a series of pedagogical lectures by leading experts on topics of significant recent interest. The previous meeting in this series took place at the Niels Bohr Institute in Copenhagen November 2022.

 

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Scientific Programme

The venue for the meeting is E-102 in the Kjølv Egelands hus. Follow this link for directions from the on-campus Hotel Ydalir.

As in previous meetings, the programme includes short talks, primarily by younger researchers, as well as lectures by invited speakers:

Extended geometry and Lie superalgebras

Jakob Palmkvist

University of Örebro

 

Quantum corrections from quotient geometry

Victoria L. Martin

University of North Florida

 

Topological Defects and Symmetries

Michele del Zotto

Uppsala University

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Reception, Lunch and Dinner

We will have a reception on the Monday evening of the event, just after the talks. It will be at the Institute of Mathematics and Physics on the 5th floor in the same building as the event. There will be nibbles and drinks at the reception, but participants are encouraged to go for dinner afterwards. See the "Dining at the University and in Stavanger" link to the left for restaurant suggestions.

A light lunch will be provided for the participants on the Tuesday of the event, at the main canteen on campus, Kafé Optimisten. We have ordered some bowls with a selection of different tastes and ingredients, including vegitarian options, served with bread and butter. 

A dinner will be organised on the Tuesday evening at 19:00. The dinner is not covered and will be in the 30-60 Euro range. We have reserved tables at the restaurant Phileas Fogg, at Skagen 27 in the center of town. They have a selection of Norwegian and international dishes, and some Vegetarian and Vegan options. There is also an option to order a Christmas dinner. If you would like to join, but have not indicated so yet, please let us know as soon as possible. 

 

Monday, 4 December

12:30 Welcome

1 Quantum corrections from quotient geometry

Recent years have seen a growing interest in fleshing out connections between black holes and number theory. Here we review a body of work that develops a new method of studying quantum corrections on quotient manifolds which uses the quotient group structure alone. The method involves building a Selberg-like zeta function for a given quotient, and showing with relative ease that this zeta function is directly related to the regularized scalar 1-loop partition function on the spacetime of interest. Further, the zeros of the Selberg zeta function label the scalar quasinormal modes. We discuss many future directions and applications of this program.

Speaker: Prof. Victoria L. Martin

VictoriaMartin.pdf

14:30 Coffee Break

2 2d CFTs, Borcherds products and hyperbolization of affine Lie algebras

In 1983, Feingold and Frenkel posed a question about possible relations between affine Lie algebras, hyperbolic Kac-Moody algebras and Siegel modular forms. We give an automorphic answer to this question and its generalization. We classify hyperbolic Borcherds-Kac-Moody superalgebras whose super-denominators define reflective automorphic products of singular weight. As a consequence, we prove that there are exactly 81 affine Lie algebras which have nice extensions to hyperbolic BKM superalgebras. We find that 69 of them appear in Schellekens’ list of holomorphic CFT of central charge 24, while 8 of them correspond to the N=1 structures of holomorphic SCFT of central charge 12 composed of 24 chiral fermions. The last 4 cases are related to exceptional modular invariants from nontrivial automorphisms of fusion algebras. This is based on a to-appear paper joint with Haowu Wang and Brandon Williams.

Speaker: Dr Kaiwen Sun

KaiwenSun.pdf

3 Heterotic ALE Instantonic Little String Theories - from Geometric Engineering in F-Theory

6D Little string theories (LSTs) are UV complete non-local theories that are decoupled from gravity with an intrinsic string scale. In this talk, I will revisit the properties of 6D (1,0) LSTs obtained from heterotic string compactifications on ALE spaces. So far, instantonic heterotic E8 × E8 theories are rarely visited due to the lack of the Lagrangian description, with the exception of a few cases explored by Aspinwall and Morrison as well as Blum and Intriligator. I will present the construction of novel heterotic E8 × E8 ALE instantonic theories using the 6D conformal matter approach. All LSTs have a continuous 2-group symmetry structure; the relevant group structure constants, combined with Coulomb and tensor branch data, provide matching criteria for those novel theories to be predicted as T-dual partners with the known Spin(32)/Z2 ALE instantonic LSTs from the theoretical perspective. Moreover, these predictions are proven by utilizing duality with the geometric engineering in F-theory, where the T-dual system is realized as the inequivalent elliptic fibration (nested elliptic K3 fibration) structure of the same geometry.

Speaker: Dr Muyang Liu

MuyangLiu.pdf

4 The Art of Slicing the Cone

While the general structure of the partition function for 4d N=2 gauge theories is by now understood using localisation, the detailed form of its various ingredients has not been worked out in full generality yet. One main difficulty is to obtain flux contributions from the localisation procedure. We solve this problem for a large class of four-manifolds B by starting with a 5d N=1theory on Sasakian S1-principal bundles over B. Here, the partition function can be expressed as a product over slices of the toric cone. Taking a Z_h-quotient along the S1 adds flat connections to the BPS locus which, in the limit of large h, become the desired flux-contributions in the 4d theory on B. Depending on how we slice the cone, the 4d theory will contain different numbers of point-like instantons and anti-instantons in the full partition function.

Speaker: Roman Mauch

16:10 Coffee Break

5 Does TTbar reproduce 2d Gravity: an Operator algebra approach

TTbar deformations are irrelevant deformations of 2d quantum field theories defined by the determinant of the stress tensor. Recent work on the TTbar deformation has shown that it can be written as a flat space version of JT gravity coupled to the undeformed theory. Furthermore, the TTbar deformation renders the deformed theory non-local. Recently, it has been shown that AdS2 JT gravity plus matter has a von Neumann factor of type II, where one can define a normalizable trace functional and compute quantities like entanglement entropy and define density matrices. Whereas, non-gravitational relativistic quantum field theory has a von Neumann factor of type III, where none of this is possible without introducing a UV cutoff. In this talk we will be exploring how TTbar deformations effect the von Neumann factor of 2d CFTs, and if they are able to reproduce a supposed signature of gravity: a von Neumann factor of type II. We will explore multiple ways of answering this question, for example a crossed product construction, and spectrum of the deformed modular hamiltonian.

Speaker: Rahul Poddar

RahulPoddar.pdf

6 Towards classical TTbar deformations for higher-derivative theories

In this talk, I will discuss classical irrelevant deformations of quantum field theories with higher-derivatives in two dimensions. The starting point will be the formal solution of the Zamolodchikov--Smirnov flow equation, which assumes the form: de Rham--Gabadadze--Tolley massive gravity plus matter, and it relies heavily on a well-defined Hilbert stress tensor. For higher-derivative theories the latter is no longer guaranteed, indicating limitations of this approach. To demonstrate this, I will briefly discuss the case of a free scalar with second order derivatives. The arising issues are easily rectified by introducing appropriate auxiliary matter fields which prove challenging to integrate out after the deformation.

Speaker: Evangelos Tsolakidis

17:30 Reception

Follow link for directions:
https://link.mazemap.com/c0LOxmHc

Tuesday, 5 December

09:00 Coffee Break

7 Extended geometry and Lie superalgebras

I will review how the concepts in differential geometry used to describe ordinary gravity can be extended in order to describe supergravity theories, in particular how ordinary diffeomorphisms can be unified with gauge transformations for the additional form fields. I will focus on how Lie superalgebras, in particular tensor hierarchy algebras, can be used even in the restriction to the bosonic sector. The lecture will to large extent be based on collaboration with Martin Cederwall.

Speaker: Prof. Jakob Palmkvist

11:00 Coffee Break

8 Unification of Decoupling Limits in M-Theory: A U-Duality Perspective

In this talk, I present a U-duality relation that connects the DLCQ of M-theory to nonrelativistic M-theory. The latter encompasses various other decoupling limits through torus compactifications, thereby establishing a novel web of dualities between matrix (gauge) theories, nonrelativistic string theory, spin matrix theory, and more. I will discuss the background geometries, the duality rules, and the physical interpretation of the decoupled theories. This web of dualities provides new insights into the BFSS conjecture and reveals previously unknown decoupling limits of M-theory. Z. Yan's talk naturally follows this presentation.

Speaker: Dr Johannes Lahnsteiner

9 Unification of Decoupling Limits in String Theory: A Worldsheet Perspective

This is Part II that follows J. Lahnsteiner’s talk. I will extend the duality web of decoupling limits in string theory by a worldsheet approach. I will start with developing the string sigma model associated with Matrix theory. T-dualizing this sigma model leads to a web connecting different corners in type II superstring theories. This duality web unifies Matrix theories (BFSS, IKKT, etc.), tensionless/ambitwistor string theory, spin Matrix theories, Carrollian strings, etc. I will also give an outlook of potential implications of this duality web for the AdS/CFT correspondence and flat space holography.

Speaker: Dr Ziqi Yan

Ziqi Yan.pdf

10 Holographic superconductors with Born-Infeld electrodynamics and noncommutative geometries.

AdS/CFT correspondence can be used to analyze condensed matter systems, one of those are the holographic superconductors. In this talk I analyze the behaviour of this type of system using an anti-de Sitter Einstein-Born-Infeld black hole with backreaction. I also present the changes in their properties that arise from using a noncommutative inspired anti-de Sitter Einstein-Born-Infeld black hole.

Speaker: Uriel Elinos

UrielElinos.pdf

12:30 Lunch

Follow link for location:
https://use.mazemap.com/#v=1&zlevel=1&center=5.692970,58.937827&zoom=18.5&campusid=33&sharepoitype=poi&sharepoi=134974

11 Topological Defects and Symmetries

I will review recent progress in our understanding of symmetries of QFTs building on the idea that symmetries are encoded in a topological subsector of the operator spectrum. I will discuss some concrete examples of topological defects, as well as the way the latter account for quantum numbers of extended operators. Along the way we will touch upon some of the more recent applications, ranging from duality defects to the higher structure of chiral symmetry.

Speaker: Prof. Michele del Zotto

MicheleDelZotto.pdf

16:00 Coffee break

12 Holographic Wilson Lines from Matter on Spheres

I will describe a family of spherical defects in four-dimensional N=4 supersymmetric Yang-Mills theory, holographically dual to probe D5- and D7-branes in AdS5 x S5. These defects carry matter fields, either hypermultiplets or simply fermions, which interact with the N=4 fields, and may loosely be thought of as strongly coupled models of fullerene molecules. I will show, using holography, that the defects undergo RG flows such that in the IR they are described by supersymmetric Wilson lines and related point-like impurities.

Speaker: Dr Ronnie Rodgers

13 Wilson Loops and Spherical Branes

In this talk, I will focus on the study of 1/2-BPS Wilson loop operators in maximally supersymmetric Yang Mills theories on (p+1)- dimensional spheres. The gravity duals to these theories are given by the backreacted geometry of spherical Dp-branes and our aim is to compute the holographic Wilson loops in these backgrounds up to next-to-leading order in the large ’t Hooft coupling expansion. This is achieved by evaluating the partition function of a probe fundamental string in these backgrounds up to one loop order, from the string theory point of view, and by comparing this to the vacuum expectation value of the supersymmetric Wilson loop from the field theory perspective.

Speaker: Alexia Nix

19:00 Conference Dinner

Follow link for location:
https://www.google.com/maps/place/Phileas+Fogg/@58.9711649,5.7280717,16.59z/data=!4m6!3m5!1s0x463a3549811bb11f:0xf37c7d7d4b0f1afb!8m2!3d58.9716667!4d5.7308333!16s%2Fg%2F1tglfx89?entry=ttu

Wednesday, 6 December

09:00 Coffee Break

14 Carrollian fluids and spontaneously broken boosts

Carrollian symmetries arise when the speed of light is taken to zero. I will describe how Carrollian fluids sponaneously break boost symmetries, which provides a unifying description that ties together several seemingly disparate notions of Carrollian fluids that have appeared previously. The associated Goldstone mode allows us to construct an effective Aristotelian geometry, implying that previous results about Aristotelian fluids can be used to describe the first-order hydrodynamics. Furthermore, this effective Aristotelian structure gives rise to a Horava-Lifshitz-like effective action for the Goldstone.

Speaker: Dr Emil Have

EmilHave.pdf

15 Leading-order gravitational radiation to all spin orders

We present the gravitational waveform produced by the scattering encounter of two classical spinning objects at leading order in Newton's constant but to all orders in the spin vectors of the objects. Our results are based on amplitudes that are compatible with known properties of Kerr black holes. We include in our analysis contact deformations of the constituent amplitudes that are needed to match the black-hole-perturbation-theory description of Kerr black holes in the super-extremal limit.

Speaker: Dr Kays Haddad

KaysHaddad.pdf

16 Kerr binary dynamics from minimal coupling and double copy

Recently there has been considerable progress in using amplitude-based techniques to extract gravitational waves templates produced by the coalescence of strongly gravitating compact objects such as black holes and neutron stars. In this talk I will show how to construct a new minimally coupled Yang Mills Lagrangian based on the introduction of a new covariant derivative that incorporates classical spin effects. Using double copy techniques we use this theory to extract gravity amplitudes and observables up to 2PM that are relevant to describe Kerr binary dynamics to all orders in the spin. If time permits, I will talk about 3PM radiation-reaction effects and radiative observables in the case of Kerr black-holes scattering, whose description naturally fits in the above-mentioned theories.

Speaker: Dr Francesco Alessio

FrancescoAlessio.pdf

17 Black Hole Ringdown in a non-Kerr geometry

In the ringdown phase of black hole binary coalescence, the remnant object is a rotating black hole. We use the Kerr metric in GR, where the mass and spin uniquely describe the black hole (no-hair theorem). However, one can model this remnant black hole with a non-Kerr metric provided that the metric is stationary and axisymmetric. The Johannsen-Psaltis metric is one such example. We go through the construction of this metric and use LIGO ringdown data to measure the values of the parameters in the Johannsen-Psaltis metric.

Speaker: Zaryab Ahmed

ZaryabAhmed.pdf

11:05 Coffee Break

18 Boundaries and Interfaces with Localized Cubic Interactions in the O(N) Model

In this talk, I will present a new approach to boundaries and interfaces in the O(N) model where we add certain localized cubic interactions. These operators are nearly marginal when the bulk is four dimensional and they explicitly break the O(N) symmetry of the bulk theory down to O(N-1). The one-loop beta functions of the cubic couplings are then modified by the quartic bulk interactions. I will present the RG analysis for both the interface and the boundary cases. In the interface case, for sufficiently large N, we find stable IR fixed points with purely imaginary cubic couplings. In the boundary case, we find real fixed points for all N. Based on arXiv:2307.00072

Speaker: Dr Sabine Harribey

SabineHarribey.pdf

19 Classifying large N limits of adjoint multi-scalar theories by algebra

We initiate a new approach to RG flows especially adapted to 4D QFT with multiple scalars and show that one-loop flows can be described in terms of a commutative but non-associative algebra. As an example, we study the algebra of a multi-scalar theory with M SU(N) adjoint scalars. The algebraic tools of idempotents and Kowalevski exponents can be used to characterize the RG flow in the area of weak scalar couplings. Using these tools we classify all large N limits of these algebras: the standard ‘t Hooft limit, a ‘multi-matrix’ limit, and an intermediate case with extra symmetry and no free parameter. The algebra identifies these limits without the need of diagrammatic or combinatorial analysis.

Speaker: Nadia Flodgren

NadiaFlodgren.pdf

20 ZOOM: Heisenberg Spin/Bosonic Chains, Gromov-Witten Invariants And Supersymmetric Gauge Theories.

In this talk, we will present how a Heisenberg spin chain emerges from the two-dimensional N=(2,2) gauge theory at an intermediate scale, which relies on the renormalization group flow guided by the global symmetries and the dynamics of domain walls. Two examples will be discussed: XX-model and its K-theoretic version. If time permits, we will also introduce a new Bethe ansatz for q-boson model.

Based on arXiv : 2212.11288,arXiv : 2311.04990

Speaker: Dr Wei Gu

WeiGu.pdf