Name: 32nd Nordic Network Meeting on "Strings, Fields and Branes"
Start: 2023-12-04T11:25:00+01:00
End: 2023-12-06T17:15:00+01:00
Location: Kjølv Egelands hus

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

from Monday, December 4, 2023 (11:25 AM) to Wednesday, December 6, 2023 (5:15 PM)

Monday, December 4, 2023

12:30 PM Welcome
Welcome
12:30 PM - 1:00 PM
Room: E-102
1:00 PM Quantum corrections from quotient geometry - Victoria L. Martin
Quantum corrections from quotient geometry
- Victoria L. Martin
1:00 PM - 2:30 PM
Room: E-102 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.
2:30 PM Coffee Break
Coffee Break
2:30 PM - 3:00 PM
Room: E-102
3:00 PM 2d CFTs, Borcherds products and hyperbolization of affine Lie algebras - Kaiwen Sun
2d CFTs, Borcherds products and hyperbolization of affine Lie algebras
- Kaiwen Sun
3:00 PM - 3:20 PM
Room: E-102 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.
3:25 PM Heterotic ALE Instantonic Little String Theories - from Geometric Engineering in F-Theory - Muyang Liu
Heterotic ALE Instantonic Little String Theories - from Geometric Engineering in F-Theory
- Muyang Liu
3:25 PM - 3:45 PM
Room: E-102 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.
3:50 PM The Art of Slicing the Cone - Roman Mauch
The Art of Slicing the Cone
- Roman Mauch
3:50 PM - 4:10 PM
Room: E-102 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.
4:10 PM Coffee Break
Coffee Break
4:10 PM - 4:40 PM
Room: E-102
4:40 PM Does TTbar reproduce 2d Gravity: an Operator algebra approach - Rahul Poddar
Does TTbar reproduce 2d Gravity: an Operator algebra approach
- Rahul Poddar
4:40 PM - 5:00 PM
Room: E-102 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.
5:05 PM Towards classical TTbar deformations for higher-derivative theories - Evangelos Tsolakidis
Towards classical TTbar deformations for higher-derivative theories
- Evangelos Tsolakidis
5:05 PM - 5:25 PM
Room: E-102 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.
5:30 PM Reception
Reception
5:30 PM - 7:30 PM
Room: Fifth floor
Tuesday, December 5, 2023

9:00 AM Coffee Break
Coffee Break
9:00 AM - 9:30 AM
Room: E-102
9:30 AM Extended geometry and Lie superalgebras - Jakob Palmkvist
Extended geometry and Lie superalgebras
- Jakob Palmkvist
9:30 AM - 11:00 AM
Room: E-102 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.
11:00 AM Coffee Break
Coffee Break
11:00 AM - 11:20 AM
Room: E-102
11:20 AM Unification of Decoupling Limits in M-Theory: A U-Duality Perspective - Johannes Lahnsteiner
Unification of Decoupling Limits in M-Theory: A U-Duality Perspective
- Johannes Lahnsteiner
11:20 AM - 11:40 AM
Room: E-102 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.
11:45 AM Unification of Decoupling Limits in String Theory: A Worldsheet Perspective - Ziqi Yan
Unification of Decoupling Limits in String Theory: A Worldsheet Perspective
- Ziqi Yan
11:45 AM - 12:05 PM
Room: E-102 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.
12:10 PM Holographic superconductors with Born-Infeld electrodynamics and noncommutative geometries. - Uriel Elinos
Holographic superconductors with Born-Infeld electrodynamics and noncommutative geometries.
- Uriel Elinos
12:10 PM - 12:30 PM
Room: E-102 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.
12:30 PM Lunch
Lunch
12:30 PM - 2:30 PM
Room: Kafé Optimisten
2:30 PM Topological Defects and Symmetries - Michele del Zotto
Topological Defects and Symmetries
- Michele del Zotto
2:30 PM - 4:00 PM
Room: E-102 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.
4:00 PM Coffee break
Coffee break
4:00 PM - 4:30 PM
Room: E-102
4:30 PM Holographic Wilson Lines from Matter on Spheres - Ronnie Rodgers
Holographic Wilson Lines from Matter on Spheres
- Ronnie Rodgers
4:30 PM - 4:50 PM
Room: E-102 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.
4:55 PM Wilson Loops and Spherical Branes - Alexia Nix
Wilson Loops and Spherical Branes
- Alexia Nix
4:55 PM - 5:15 PM
Room: E-102 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.
7:00 PM Conference Dinner
Conference Dinner
7:00 PM - 9:30 PM
Wednesday, December 6, 2023

9:00 AM Coffee Break
Coffee Break
9:00 AM - 9:30 AM
Room: E-102
9:30 AM Carrollian fluids and spontaneously broken boosts - Emil Have
Carrollian fluids and spontaneously broken boosts
- Emil Have
9:30 AM - 9:50 AM
Room: E-102 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.
9:55 AM Leading-order gravitational radiation to all spin orders - Kays Haddad
Leading-order gravitational radiation to all spin orders
- Kays Haddad
9:55 AM - 10:15 AM
Room: E-102 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.
10:20 AM Kerr binary dynamics from minimal coupling and double copy - Francesco Alessio
Kerr binary dynamics from minimal coupling and double copy
- Francesco Alessio
10:20 AM - 10:40 AM
Room: E-102 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.
10:45 AM Black Hole Ringdown in a non-Kerr geometry - Zaryab Ahmed
Black Hole Ringdown in a non-Kerr geometry
- Zaryab Ahmed
10:45 AM - 11:05 AM
Room: E-102 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.
11:05 AM Coffee Break
Coffee Break
11:05 AM - 11:25 AM
Room: E-102
11:25 AM Boundaries and Interfaces with Localized Cubic Interactions in the O(N) Model - Sabine Harribey
Boundaries and Interfaces with Localized Cubic Interactions in the O(N) Model
- Sabine Harribey
11:25 AM - 11:45 AM
Room: E-102 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
11:50 AM Classifying large N limits of adjoint multi-scalar theories by algebra - Nadia Flodgren
Classifying large N limits of adjoint multi-scalar theories by algebra
- Nadia Flodgren
11:50 AM - 12:10 PM
Room: E-102 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.
12:15 PM ZOOM: Heisenberg Spin/Bosonic Chains, Gromov-Witten Invariants And Supersymmetric Gauge Theories. - Wei Gu
ZOOM: Heisenberg Spin/Bosonic Chains, Gromov-Witten Invariants And Supersymmetric Gauge Theories.
- Wei Gu
12:15 PM - 12:35 PM
Room: E-102 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