“Strings, CFT & Integrability”
Fall Semester 2019
Organised by: Niklas Beisert, Matthias Gaberdiel, Daniel Medina, Hagen Münkler
day
date
date
time
venue
venue
speaker
title
title
Wed
18.09.
11:30
HIT E41.1
Christian Ferko (University of Chicago)
“T Tbar and Supercurrent-Squared”
abstract (click to view)
The T Tbar deformation of 2D QFTs offers a rare example of an irrelevant deformation where one has some control over the deformed theory. In addition, T Tbar has tantalizing connections to string theory -- the T Tbar deformation of a free scalar, for instance, gives the Nambu-Goto action. It is natural to wonder whether this deformation can be generalized to higher dimensions, although the most straightforward higher-dimensional analogue lacks the magical properties of the two-dimensional version.
In this talk, I will present a manifestly supersymmetric version of T Tbar, called "supercurrent-squared," which can be defined for SUSY field theories in any number of dimensions. There is some evidence -- such as the relationship between 4D supercurrent-squared and the SUSY DBI action -- that this deformation has properties similar to those of T Tbar in higher-dimensional theories. I will also discuss connections between supercurrent-squared and nonlinearly realized supersymmetry, which suggests that these deformations are related to spontaneous symmetry breaking. (click to hide)
In this talk, I will present a manifestly supersymmetric version of T Tbar, called "supercurrent-squared," which can be defined for SUSY field theories in any number of dimensions. There is some evidence -- such as the relationship between 4D supercurrent-squared and the SUSY DBI action -- that this deformation has properties similar to those of T Tbar in higher-dimensional theories. I will also discuss connections between supercurrent-squared and nonlinearly realized supersymmetry, which suggests that these deformations are related to spontaneous symmetry breaking. (click to hide)
Wed
02.10.
11:30
HIT E41.1
Kasia Rejzner (York University)
“Perturbative algebraic quantum field theory – a new paradigm for perturbative QFT”
abstract (click to view)
In this talk I will present the framework of perturbative algebraic quantum field theory (pAQFT), which is a mathematically rigorous formulation of perturbative QFT, inspired by the local quantum physics paradigm of Haag and Kastler. In recent years this framework has been successfully applied to QFT on curved spacetimes and can even be used to study some features of quantum gravity. (click to hide)
Tue
08.10.
11:30
HIT E41.1
Stefano Massai (ETH Zürich)
“Phases of little string theory and fuzzballs”
abstract (click to view)
Resolved A-type singularities admit an exact description in worldsheet string theory that regularises the linear dilaton throat dual to little string theory. A generalisation of this mechanism offers a weakly coupled description of “fuzzball” states in the Hilbert space of two and three-charge black holes. These constructions reveal stringy excitations that become light at the threshold of horizon formation and provide a glimpse of the entropic long string sector in the gravity regime. A unifying twelve dimensional description of black hole microstates emerges. (click to hide)
Wed
16.10.
11:30
HIT E41.1
Adwait Gaikwad (Tata Institute)
“Gravitational collapse in SYK models and Choptuik-like phenomenon”
Tue
22.10.
11:30
HIT E41.1
Oleg Evnin (Chulalongkorn University)
“Resonant weakly nonlinear dynamics in AdS”
abstract (click to view)
The fully resonant spectrum of normal mode frequencies for linearized
fields in Anti-de Sitter spacetime (AdS) leads to an enhancement of
nonlinear interactions, so that arbitrarily small nonlinearities may
produce large effects if one waits long enough. For gravitating
perturbations, this is believed to lead to black hole formation
starting from arbitrarily small perturbations in some cases. The
problem has attracted a considerable amount of attention due to its
role as a dual picture for holographic thermalization in conformal
field theories (CFTs) on spheres, its conceptual importance in
mathematical general relativity, and its connection to studies of
turbulent nonlinear flows of energy in contemporary PDE mathematics.
Close parallels exist with dynamics of nonlinear wave equations in
AdS, and with nonlinear Schrödinger equations in harmonic potentials,
the latter being of significance for condensed matter physics.
I will describe the resonant approximation that accurately captures
the relevant dynamics of nonlinear AdS problems over long (but
limited) times in the weakly nonlinear regime. I will then present a
few characteristic behaviors of the resulting resonant systems: finite
time turbulent blow-ups that encode black hole formation in general
relativity, Fermi-Pasta-Ulam-like returns of energy that very
accurately (but not exactly) reconstruct the initial configuration and
would present an obstruction to thermalization in dual CFTs, and cases
where special exact solutions of the resonant system can be obtained,
exhibiting exactly periodic sequences of direct and reverse cascades
of energy. (click to hide)
fields in Anti-de Sitter spacetime (AdS) leads to an enhancement of
nonlinear interactions, so that arbitrarily small nonlinearities may
produce large effects if one waits long enough. For gravitating
perturbations, this is believed to lead to black hole formation
starting from arbitrarily small perturbations in some cases. The
problem has attracted a considerable amount of attention due to its
role as a dual picture for holographic thermalization in conformal
field theories (CFTs) on spheres, its conceptual importance in
mathematical general relativity, and its connection to studies of
turbulent nonlinear flows of energy in contemporary PDE mathematics.
Close parallels exist with dynamics of nonlinear wave equations in
AdS, and with nonlinear Schrödinger equations in harmonic potentials,
the latter being of significance for condensed matter physics.
I will describe the resonant approximation that accurately captures
the relevant dynamics of nonlinear AdS problems over long (but
limited) times in the weakly nonlinear regime. I will then present a
few characteristic behaviors of the resulting resonant systems: finite
time turbulent blow-ups that encode black hole formation in general
relativity, Fermi-Pasta-Ulam-like returns of energy that very
accurately (but not exactly) reconstruct the initial configuration and
would present an obstruction to thermalization in dual CFTs, and cases
where special exact solutions of the resonant system can be obtained,
exhibiting exactly periodic sequences of direct and reverse cascades
of energy. (click to hide)
Wed
23.10.
11:15
HIT E41.1
Dmitry Galakhov (MIPT Moscow)
“BPS Hall algebra of scattering Hall states”
abstract (click to view)
Starting with a very pedestrian point of view we compare two
different at the first glance definitions for an algebra associated to
BPS states in supersymmetric fields theories. One proposed by Harvey and
Moore exploits scattering matrices of BPS states as structure constants of
a new algebra. Another one proposed by Kontsevich and Soibelman gives a
construction according to the structure of cohomological Hall algebras.
We show these two constructions give equivalent algebras. (click to hide)
different at the first glance definitions for an algebra associated to
BPS states in supersymmetric fields theories. One proposed by Harvey and
Moore exploits scattering matrices of BPS states as structure constants of
a new algebra. Another one proposed by Kontsevich and Soibelman gives a
construction according to the structure of cohomological Hall algebras.
We show these two constructions give equivalent algebras. (click to hide)
Wed
30.10.
Dalimil Mazac (YITP Stony Brook)
“Sphere packing, modular bootstrap and extremal functionals”
abstract (click to view)
I will prove a new theorem about 2D CFTs: Every unitary 2D CFT
must contain a non-trivial Virasoro primary of scaling dimension at most
c/8 + 1/2, where c is the central charge. At large c, this is an
improvement of the Hellerman bound c/6 + O(1), and is relevant for
constraining the spectrum of gravitational theories in AdS3. The proof
follows from the modular bootstrap and uses analytic extremal functionals,
originally developed in the context of four-point SL(2) conformal
bootstrap. In the second part of the talk, I will discuss a surprising
connection between modular bootstrap and the sphere-packing problem from
discrete geometry. In particular, the above bound on the gap becomes a
bound on the sphere-packing density. In 8 and 24 dimensions, this bound is
sharp and leads to a solution of the sphere-packing problem in these
dimensions, as originally proved by Viazovska et al. Time allowing, I will
discuss a generalization of the analytic functional method to
higher-dimensional CFTs. (click to hide)
must contain a non-trivial Virasoro primary of scaling dimension at most
c/8 + 1/2, where c is the central charge. At large c, this is an
improvement of the Hellerman bound c/6 + O(1), and is relevant for
constraining the spectrum of gravitational theories in AdS3. The proof
follows from the modular bootstrap and uses analytic extremal functionals,
originally developed in the context of four-point SL(2) conformal
bootstrap. In the second part of the talk, I will discuss a surprising
connection between modular bootstrap and the sphere-packing problem from
discrete geometry. In particular, the above bound on the gap becomes a
bound on the sphere-packing density. In 8 and 24 dimensions, this bound is
sharp and leads to a solution of the sphere-packing problem in these
dimensions, as originally proved by Viazovska et al. Time allowing, I will
discuss a generalization of the analytic functional method to
higher-dimensional CFTs. (click to hide)
Mon
04.11.
Thomas Fischbacher (Google Research Zürich)
Theoretical Physics Colloquium: “Studying Spontaneous Symmetry Breaking with Machine Learning Tools”
abstract (click to view)
Modern Machine Learning software libraries such as Google's TensorFlow can be employed to greatly simplify the analysis of high-dimensional scalar sectors of some M-Theory compactifications. This talk gives an overview over recent insights into the structure of N=8 SO(8) de Wit-Nicolai Supergravity that have been obtained in this way. We will also look into using readily available Google Research tools to easily obtain new results by modifying pedagogical code examples that have been published alongside our recent comprehensive study of SO(8) supergravity equilibria. (click to hide)
Tue
05.11.
11:30
HIT E41.1
Marc-Antoine Fiset
“Superconformal algebras for twisted connected sums and G2 mirror symmetry”
abstract (click to view)
Early hints of mirror symmetry for Calabi-Yau manifolds arose from studying
the algebra of chiral symmetries of the worldsheet theory describing
strings on these geometries. In 1809.06376
<https://arxiv.org/abs/1809.06376>, which the talk will be about, I perform
a similar analysis, replacing Calabi-Yau manifolds by 7-dimensional G2
holonomy spaces constructed via the twisted connected sum method of Corti,
Haskins, Nordström, and Pacini. Besides connecting nicely with recent
results on the conjectured mirror symmetry for G2, this work is a necessary
step for applications of twisted connected sums in string theory. (click to hide)
the algebra of chiral symmetries of the worldsheet theory describing
strings on these geometries. In 1809.06376
<https://arxiv.org/abs/1809.06376>, which the talk will be about, I perform
a similar analysis, replacing Calabi-Yau manifolds by 7-dimensional G2
holonomy spaces constructed via the twisted connected sum method of Corti,
Haskins, Nordström, and Pacini. Besides connecting nicely with recent
results on the conjectured mirror symmetry for G2, this work is a necessary
step for applications of twisted connected sums in string theory. (click to hide)
Wed
06.11.
11:30
HIT E41.1
Sylvain Lacroix (Universität Hamburg)
“Integrable coupled sigma-models from affine Gaudin models”
abstract (click to view)
In this seminar, I will discuss integrable systems called affine Gaudin models and their application to the study of integrable sigma models. As an introductory example, I will first discuss a simpler class of Gaudin models, the finite ones, and their relation with integrable spin chains and mechanical systems. I will then explain how to use affine Gaudin models to construct new integrable classical sigma models, by coupling together an arbitrary number of principal chiral models with Wess-Zumino terms. (click to hide)
Wed
13.11.
11:30
HIT E41.1
Nat Levine (Imperial College)
“Integrable sigma models and 2-loop RG flow”
abstract (click to view)
It is often suggested that integrable 2d sigma models should be renormalizable, however this relationship has only previously been checked in the 1-loop approximation. The aim of this work is to understand what happens beyond 1-loop. Based on the examples of the lambda- and eta-models, we confirm that classically integrable models appear to be 2-loop renormalizable if supplemented with particular finite local counterterms, i.e. quantum corrections to the target space geometry. The lambda-model is further studied as a sigma model on a "tripled" target space where extra symmetries become manifest, enforcing renormalizability without the need for extra counterterms. Its 2-loop beta-function is computed, matching the known results for groups and symmetric spaces in the limit when the lambda-model becomes the corresponding non-abelian dual model. This leads to the statement that non-abelian duality commutes with the RG flow beyond 1-loop order. (click to hide)
Wed
20.11.
11:45
HIT E41.1
Usman Naseer (MIT / Uppsala University)
“On the UV-finiteness of entanglement entropy in string theory”
abstract (click to view)
Entanglement entropy in a local quantum field theory with a background
spacetime suffers from UV divergences. Arguments based on black hole
physics, however, suggest that entanglement entropy in a quantum theory of
gravity should be finite. We use string field theory to study properties of
entanglement entropy in string theory and show that the entanglement
entropy of closed bosonic strings is UV-finite. (click to hide)
spacetime suffers from UV divergences. Arguments based on black hole
physics, however, suggest that entanglement entropy in a quantum theory of
gravity should be finite. We use string field theory to study properties of
entanglement entropy in string theory and show that the entanglement
entropy of closed bosonic strings is UV-finite. (click to hide)
Tue
26.11.
11:45
HIT E41.1
Nicolai Reshetikhin (University of California Berkeley)
“Semiclassical eigenfunctions of quantum integrable systems and the Poisson sigma model”
abstract (click to view)
Poisson sigma model is a two dimensional topological field theory with the target being a Poisson manifold. As it was shown by Cattaneo and Felder,
the partition function with certain boundary conditions gives the Kontsevich's star product quantization of functions on the target Poisson manifold. In the talk I will explain how a different choice of boundary conditions gives semiclassical expansion of eigenfunctions of any given quantum integrable
system. (based on ongoing work with A. Cattaneo and P. Mnev). (click to hide)
the partition function with certain boundary conditions gives the Kontsevich's star product quantization of functions on the target Poisson manifold. In the talk I will explain how a different choice of boundary conditions gives semiclassical expansion of eigenfunctions of any given quantum integrable
system. (based on ongoing work with A. Cattaneo and P. Mnev). (click to hide)
Wed
27.11.
Fedor Levkovich-Maslyuk (ENS Paris)
“Towards Structure Constants in N=4 SYM via Quantum Spectral Curve”
abstract (click to view)
The Quantum Spectral Curve (QSC) is a powerful integrability-based
framework capturing the nonperturbative spectrum of planar N=4 SYM theory.
We present first evidence that it should also play an important role for
computing exact correlation functions. We compute the correlator of 3
scalar local operators connected by Wilson lines forming a triangle in the
ladders limit, and show that it massively simplifies when written in terms
of the QSC. The final all-loop result takes a very compact form, suggesting
its interpretation via Sklyanin's separation of variables (SoV). We discuss
work in progress on extending these results to local operators. We also
derive, for the first time, the SoV measure for su(N) noncompact and
compact spin chains. (click to hide)
framework capturing the nonperturbative spectrum of planar N=4 SYM theory.
We present first evidence that it should also play an important role for
computing exact correlation functions. We compute the correlator of 3
scalar local operators connected by Wilson lines forming a triangle in the
ladders limit, and show that it massively simplifies when written in terms
of the QSC. The final all-loop result takes a very compact form, suggesting
its interpretation via Sklyanin's separation of variables (SoV). We discuss
work in progress on extending these results to local operators. We also
derive, for the first time, the SoV measure for su(N) noncompact and
compact spin chains. (click to hide)
Wed
04.12.
Volker Schomerus (DESY Hamburg)
“Integrability of Conformal Partial Wave Expansions”
Wed
11.12.
Alejandra Castro (University of Amsterdam)
“The Holographic Landscape of Symmetric Product Orbifolds”
abstract (click to view)
I will discuss the application of Siegel paramodular forms to constructing new examples of holography. These forms are relevant to investigate the growth of coefficients in the elliptic genus of symmetric product orbifolds at large central charge. The main finding is that the landscape of symmetric product theories decomposes into two regions. In one region, the growth of the low energy states is Hagedorn, which indicates a stringy dual. In the other, the growth is much slower, and compatible with the spectrum of a supergravity theory on AdS3. I will provide a simple diagnostic which places any symmetric product orbifold in either region. The examples I will present open a path to novel realizations of AdS3/CFT2. (click to hide)
last modified: Thu, 2 Jan 2020, 16:40 CET