“QFT, Strings and Beyond”
Spring Semester 2024
Organised by: Niklas Beisert, Johannes Broedel, Sibylle Driezen, Matthias Gaberdiel, Edward Mazenc
day
date
date
time
venue
venue
speaker
title
title
Wed
28.02.
14:00
HIT E41.1
Vladimir Kazakov (ENS Paris)
“Principal chiral model in arbitrary magnetic field: exact solution in planar limit”
abstract (click to view)
The two-dimensional Principal Chiral Model (PCM) has been considered since long as an instructive example of a QFT bearing certain similarities with QCD: asymptotic freedom, dimensional transmutation with a physical mass spectrum and a non-trivial 't Hooft's large N limit. In addition, it is an integrable QFT, with the known physical S-matrix. In our 1994 paper with V.Fateev and P.Wiegmann, we found not only the exact but also explicit solution of the vacuum energy of SU(N)xSU(N) PCM in the 't Hooft limit in the presence of specific, albeit arbitrary strong, "magnetic" field (the chemical potential of density of physical particles). The shape of this field repeated the Perron-Frobenius (PF) mode on the su(N) Dynkin diagram. I will present our recent work with E.Sobko and K.Zarembo (arxiv:2312.04801) where we explicitly solved the Bethe equation for the magnetic field of arbitrary shape. We also studied this solution in the case of small deviations of the magnetic field from the PF mode and found a perfect correspondence with the known perturbative and strong coupling results. I will also mention our results of 1/N expansion of the energy and a possible interpretation of PCF as a 2+1-dimensional noncritical string theory, where the role of the 3rd dimension is played by Dynkin diagram. (click to hide)
Wed
06.03.
14:00
HIT E41.1
Petr Kravchuk (King’s College London)
“AdS three-body problem at large spin”
abstract (click to view)
Motivated by the problem of understanding multi-twist operators in general CFTs, I will discuss the interacting spectrum of large-spin three-particle states in AdS. In particular, I will explain that thanks to the AdS curvature this particular limit of the three-body problem is tractable. The large spin limit effectively becomes a semiclassical limit of a Berezin-Toeplitz Hamiltonian, which allows us to analyze the leading-twist spectrum analytically. Work in progress with Jeremy Mann. (click to hide)
Thu
07.03.
12:30
HIT E41.1
Fedor Popov (New York University)
“Holography on the Quantum Disk”
abstract (click to view)
Motivated by recent study of DSSYK and the non-commutative nature of its bulk dual, I will review and analyze an example of a non-commutative spacetime known as the quantum disk proposed by L. Vaksman. The quantum disk is defined as the space whose isometries are generated by the quantum algebra U_q(su_{1,1}). I will review how this algebra is defined and its associated group SL_q(2) that it generates, highlighting its non-trivial coproduct that sources bulk non-commutativity. After that I will analyze the structure of holography on the quantum disk and study the imprint of non-commutativity on the putative boundary dual. (click to hide)
Wed
13.03.
14:00
HIT E41.1
Michele Galli (Humboldt U. Berlin)
“Consistent truncations and KK spectra via exceptional field theory”
abstract (click to view)
In this seminar I will discuss how Exceptional field theory provides us with a natural framework to study AdS vacua and their CFT duals. I will start with a review of consistent truncations and their construction in ExFT, I will then describe two recent examples. In the first we constructed a new consistent truncation of type IIB supergravity on S^3xS^3xS^1. We then found several families of AdS3 vacua preserving various amounts of supersymmetry in 3 dimensions and uplifted the solutions to 10 d. In the second example we found a domain wall solution interpolating between the squashed and round S^^7 vacua of 11 d supergravity. We then used the machinery of KK spectrometry to compute the quadratic couplings of fluctuations along the flow. (click to hide)
Wed
20.03.
14:00
HIT E41.1
Victor Gorbenko (EPFL Lausanne)
“Quantum groups as global symmetries”
abstract (click to view)
We would like to answer the following question: can a global internal symmetry of a quantum filed theory be a quantum group, and if yes, what are the the consequences of such symmetry? We discuss a concrete example where this situation is realized in a non-local and non-unitary 2D CFT. This allows us to derive constraints that are similar to the case of usual symmetries and that should be satisfied by a quantum-group-symmetric theory generically. (click to hide)
Wed
27.03.
14:00
HIT E41.1
Yoann Sohnle Moreno (Uppsala University)
“Solving a Feynman integral depending on two elliptic curves: the 5 mass Kite family”
abstract (click to view)
We consider the 5-mass kite family of self-energy Feynman integrals and present a systematic approach for putting its associated differential equation into a convenient form (also called the epsilon or canonical form).
We show that this is most easily achieved by making a change of variables from the kinematic space to the function space of two tori with punctures.
We demonstrate how the locations of relevant punctures on these tori, which are required to parametrize the full image of the kinematic space onto this moduli space, can be extracted from integrals over the solution of homogeneous differential equations (also called maximal cuts).
A boundary value is provided to systematically solve the differential equation in terms of iterated integrals over so-called Kronecker-Eisenstein coefficients -- the equivalents of rational functions on a torus. (click to hide)
We show that this is most easily achieved by making a change of variables from the kinematic space to the function space of two tori with punctures.
We demonstrate how the locations of relevant punctures on these tori, which are required to parametrize the full image of the kinematic space onto this moduli space, can be extracted from integrals over the solution of homogeneous differential equations (also called maximal cuts).
A boundary value is provided to systematically solve the differential equation in terms of iterated integrals over so-called Kronecker-Eisenstein coefficients -- the equivalents of rational functions on a torus. (click to hide)
Wed
17.04.
14:00
HIT E41.1
Saskia Demulder (Ben Gurion U.)
“R-defects: topological defects in non-Abelian Chern-Simons”
abstract (click to view)
Topological defects defy our conventional understanding of what symmetries are. Known topological defects are however mostly confined to discrete or Abelian continuous and compact groups. We construct a new class of topological defects in the Chern Simons theory with non-Abelian, non-compact gauge groups. This new class of defects are characterised by a solution of the so-called modified-classical Yang-Baxter equation and are thus linked to Lagrangian subalgebras. This algebraic description enables us to tackle their fusion algebra both using a Lagrangian path integral and an Hamiltonian perspective. If time permits we will discuss possible applications to 3d gravity and its higher spin generalisation.
This is work in progress with A.S. Arvanitakis, L.T. Cole, and D.C. Thompson. (click to hide)
This is work in progress with A.S. Arvanitakis, L.T. Cole, and D.C. Thompson. (click to hide)
Wed
24.04.
14:00
HIT E41.1
Nejc Ceplak (Trinity College Dublin)
“Black Hole Singularity from OPE”
abstract (click to view)
Eternal asymptotically AdS black holes are dual to thermofield double states on the boundary CFT. It has long been known that black hole singularities have certain signatures in boundary thermal two-point functions via the so-called bouncing geodesics. However, the understanding of these signatures from the CFT point of view has been elusive. In this talk I will try present some progress in answering this question.
I will analyse the boundary CFT correlation function of scalar operators and decompose them using the Operator Product Expansion (OPE). I will show that the stress-tensor sector of the correlator develops singularities precisely at the points that are connected by bulk bouncing geodesics. This means that black hole singularities are encoded in the analytic behavior of the boundary correlators determined by multiple stress tensor exchanges.
Furthermore, I will show that in the limit where the conformal dimension of the operators is large, the stress-tensor contribution develops a branch point singularity as predicted by the geodesic analysis. I will also argue that the appearance of complexified geodesics, which play an important role in computing the full correlator, is related to the contributions
of the double-trace operators in the boundary CFT. (click to hide)
I will analyse the boundary CFT correlation function of scalar operators and decompose them using the Operator Product Expansion (OPE). I will show that the stress-tensor sector of the correlator develops singularities precisely at the points that are connected by bulk bouncing geodesics. This means that black hole singularities are encoded in the analytic behavior of the boundary correlators determined by multiple stress tensor exchanges.
Furthermore, I will show that in the limit where the conformal dimension of the operators is large, the stress-tensor contribution develops a branch point singularity as predicted by the geodesic analysis. I will also argue that the appearance of complexified geodesics, which play an important role in computing the full correlator, is related to the contributions
of the double-trace operators in the boundary CFT. (click to hide)
Thu
02.05.
12:30
HIT E41.1
Jnan Maharana (Bhubaneswar, NISER)
“Production of KK states in large radius compactification scenario”
abstract (click to view)
We consider production of Kaluza-Klein states at LHC in the Large Radius
Compactification scenario. In thi proposal the compactification scale
could be in the TeV range. Therefore, some of the predictions can be
subject to experimental tests at LHC. Thousands of models have been proposed following the papers of ADD and AADD. We derive boulds on (a)
total cross sections for production of KK states and (b) differential cross section for this inelastic reaction from general principles of local field theories. The results have minimal model dependent. There are intricate problems in study of inelastic unequal mass scatterings. Attentions will be paid to overcome the associated problems. (click to hide)
Compactification scenario. In thi proposal the compactification scale
could be in the TeV range. Therefore, some of the predictions can be
subject to experimental tests at LHC. Thousands of models have been proposed following the papers of ADD and AADD. We derive boulds on (a)
total cross sections for production of KK states and (b) differential cross section for this inelastic reaction from general principles of local field theories. The results have minimal model dependent. There are intricate problems in study of inelastic unequal mass scatterings. Attentions will be paid to overcome the associated problems. (click to hide)
Wed
08.05.
14:00
HIT E41.1
Enrico Pajer (U. of Cambridge)
t.b.a.
Wed
15.05.
14:00
HIT E41.1
Alexander Tumanov (LPENS Paris)
t.b.a.
Wed
22.05.
14:00
HIT E41.1
Carlos Mafra (Southampton U.)
t.b.a.
last modified: Wed, 24 Apr 2024, 18:54 CEST