Triangle Seminars
December 2017
Thu
14 Dec 2017
Branes and the Kraft-Procesi transition
Santiago Cabrera Marquez
(Imperial College London)
Abstract:
Type IIB superstring brane configurations can have a low energy dynamics described by an effective 3d N=4 gauge theory. The moduli space of the gauge theory is normally a Hyperkähler variety. Singular points in the variety correspond to brane configurations where some fields become massless, giving rise to the Higgs mechanism. I will explain the relevance of a set of theories whose moduli space is the closure of a nilpotent orbit of Lie(F), where F is the flavour symmetry group of the theory. I will show how the mathematical description of the "transverse slice" between two nilpotent orbits can be understood in terms of brane dynamics as a realisation of the Higgs mechanism.
Type IIB superstring brane configurations can have a low energy dynamics described by an effective 3d N=4 gauge theory. The moduli space of the gauge theory is normally a Hyperkähler variety. Singular points in the variety correspond to brane configurations where some fields become massless, giving rise to the Higgs mechanism. I will explain the relevance of a set of theories whose moduli space is the closure of a nilpotent orbit of Lie(F), where F is the flavour symmetry group of the theory. I will show how the mathematical description of the "transverse slice" between two nilpotent orbits can be understood in terms of brane dynamics as a realisation of the Higgs mechanism.
Posted by: QMW
Wed
13 Dec 2017
Generalized Wilson loops in N=4 SYM and correlators on a line
📍 London
Arkady Tseytlin
(Imperial College)
Abstract:
We will discuss generalized circular Wilson loops and 1d CFT defined by correlators of operators inserted along the loop following arXiv:1706.00756 and some more recent work.
We will discuss generalized circular Wilson loops and 1d CFT defined by correlators of operators inserted along the loop following arXiv:1706.00756 and some more recent work.
Posted by: KCL
Fri
8 Dec 2017
Graduate Mini-course: Holographic combinatorics : 2d Yang Mills theory to tensor models via AdS/CFT
Sanjaye Ramgoolam
(QMUL)
Abstract:
These lectures will be focused on aspects of combinatorics relevant to gauge-string duality (holography).
The physical theories we will discuss include two dimensional Yang Mills
theory, four-dimensional N=4 super Yang Mills
theory with U(N) gauge group, Matrix and tensor models.
The key mathematical concepts include : Schur Weyl-duality,
permutation equivalence classes and associated discrete Fourier
transforms as an approach to counting problems and, branched covers and
Hurwitz spaces. Schur-Weyl duality is a powerful relation between
representations of U(N) and representations of symmetric groups.
Representation theory of symmetric groups offers a method to
define nice bases for functions on equivalence classes of permutations.
These bases are useful in counting gauge invariant functions of
matrices or tensors, as well as computing their correlators in physical
theories. In AdS/CFT these bases have proved useful in identifying
local operators in gauge-theory dual to giant gravitons in AdS.
In the simplest cases of gauge-string duality, the known mathematics
of branched covers and Hurwitz spaces provide the mechanism for the
holographic correspondence between gauge invariants and stringy geometry.
(Lecture 3: Hermitian matrix model. Tensor models and Permutation centralizer al- gebras. Using permutation equivalences to count matrix/tensor invariants and compute correlators. Relations to covering spaces.)
These lectures will be focused on aspects of combinatorics relevant to gauge-string duality (holography).
The physical theories we will discuss include two dimensional Yang Mills
theory, four-dimensional N=4 super Yang Mills
theory with U(N) gauge group, Matrix and tensor models.
The key mathematical concepts include : Schur Weyl-duality,
permutation equivalence classes and associated discrete Fourier
transforms as an approach to counting problems and, branched covers and
Hurwitz spaces. Schur-Weyl duality is a powerful relation between
representations of U(N) and representations of symmetric groups.
Representation theory of symmetric groups offers a method to
define nice bases for functions on equivalence classes of permutations.
These bases are useful in counting gauge invariant functions of
matrices or tensors, as well as computing their correlators in physical
theories. In AdS/CFT these bases have proved useful in identifying
local operators in gauge-theory dual to giant gravitons in AdS.
In the simplest cases of gauge-string duality, the known mathematics
of branched covers and Hurwitz spaces provide the mechanism for the
holographic correspondence between gauge invariants and stringy geometry.
(Lecture 3: Hermitian matrix model. Tensor models and Permutation centralizer al- gebras. Using permutation equivalences to count matrix/tensor invariants and compute correlators. Relations to covering spaces.)
Posted by: QMW
Wed
6 Dec 2017
Holographic Phonons
Matteo Baggioli
(University of Crete)
Abstract:
We discuss the presence of phonons and
the interplay between spontaneous and explicit breaking
of translations in the context of holography.
Using two different bottom-up models we show the existence of
transverse and longitudinal phonons, whose properties are in
perfect agreement with elastic theory and hydrodynamics.
We focus our attention on the elastic and transport features
of the dual QFT also in the presence of a small explicit breaking.
We conclude speculating about the possibility of having
gravitational duals for strongly coupled viscoelastic materials.
We discuss the presence of phonons and
the interplay between spontaneous and explicit breaking
of translations in the context of holography.
Using two different bottom-up models we show the existence of
transverse and longitudinal phonons, whose properties are in
perfect agreement with elastic theory and hydrodynamics.
We focus our attention on the elastic and transport features
of the dual QFT also in the presence of a small explicit breaking.
We conclude speculating about the possibility of having
gravitational duals for strongly coupled viscoelastic materials.
Posted by: IC
Wed
6 Dec 2017
Handling Handles: Nonplanar Integrability
📍 London
Joao Caetano
(ENS, Paris)
Abstract:
TRIANGULAR SEMINAR: We propose an integrability setup for the computation of correlation functions of gauge-invariant operators at any value of the 't Hooft coupling and at any order in the large Nc 't Hooft expansion in N = 4 SYM theory. In this multi-step proposal, one polygonizes the string worldsheet in all possible ways, hexagonalizes all resulting polygons, and sprinkles mirror particles over all hexagon junctions to obtain the full correlator. We test our integrability-based conjecture against a non-planar four-point correlator of large half-BPS operators at one and two loops.
TRIANGULAR SEMINAR: We propose an integrability setup for the computation of correlation functions of gauge-invariant operators at any value of the 't Hooft coupling and at any order in the large Nc 't Hooft expansion in N = 4 SYM theory. In this multi-step proposal, one polygonizes the string worldsheet in all possible ways, hexagonalizes all resulting polygons, and sprinkles mirror particles over all hexagon junctions to obtain the full correlator. We test our integrability-based conjecture against a non-planar four-point correlator of large half-BPS operators at one and two loops.
Posted by: KCL
Wed
6 Dec 2017
Phases of Matrix Quantum Mechanics and Quantum Gravitational Collapse from the new Large D Limit
📍 London
Frank Ferrari
(Universite Libre de Bruxelles, Intl. Solvay Inst., IBS)
Abstract:
TRIANGULAR SEMINAR:
New techniques of large N and large D allow to study analytically planar matrix quantum mechanics at strong coupling in a reliable way. Using these techniques, we found a remarkable phase transition in these systems, which is very naturally interpreted as a quantum version of the phenomenon of black hole formation in a gravitational collapse.
<br>
Based on 1701.01171, 1707.03431, 1709.07366, 1710.07263 and work in progress.
TRIANGULAR SEMINAR:
New techniques of large N and large D allow to study analytically planar matrix quantum mechanics at strong coupling in a reliable way. Using these techniques, we found a remarkable phase transition in these systems, which is very naturally interpreted as a quantum version of the phenomenon of black hole formation in a gravitational collapse.
<br>
Based on 1701.01171, 1707.03431, 1709.07366, 1710.07263 and work in progress.
Posted by: KCL
Fri
1 Dec 2017
Graduate Mini-course: Holographic combinatorics : 2d Yang Mills theory to tensor models via AdS/CFT
Sanjaye Ramgoolam
(QMUL)
Abstract:
These lectures will be focused on aspects of combinatorics relevant to gauge-string duality (holography).
The physical theories we will discuss include two dimensional Yang Mills
theory, four-dimensional N=4 super Yang Mills
theory with U(N) gauge group, Matrix and tensor models.
The key mathematical concepts include : Schur Weyl-duality,
permutation equivalence classes and associated discrete Fourier
transforms as an approach to counting problems and, branched covers and
Hurwitz spaces. Schur-Weyl duality is a powerful relation between
representations of U(N) and representations of symmetric groups.
Representation theory of symmetric groups offers a method to
define nice bases for functions on equivalence classes of permutations.
These bases are useful in counting gauge invariant functions of
matrices or tensors, as well as computing their correlators in physical
theories. In AdS/CFT these bases have proved useful in identifying
local operators in gauge-theory dual to giant gravitons in AdS.
In the simplest cases of gauge-string duality, the known mathematics
of branched covers and Hurwitz spaces provide the mechanism for the
holographic correspondence between gauge invariants and stringy geometry.
(Lecture 2: Local gauge invariant operators and Hilbert space of CFTs. Young diagrams and Brane geometries. Half-BPS and quarter-BPS. Counting, construction and correlators in group theoretic combinatorics.)
These lectures will be focused on aspects of combinatorics relevant to gauge-string duality (holography).
The physical theories we will discuss include two dimensional Yang Mills
theory, four-dimensional N=4 super Yang Mills
theory with U(N) gauge group, Matrix and tensor models.
The key mathematical concepts include : Schur Weyl-duality,
permutation equivalence classes and associated discrete Fourier
transforms as an approach to counting problems and, branched covers and
Hurwitz spaces. Schur-Weyl duality is a powerful relation between
representations of U(N) and representations of symmetric groups.
Representation theory of symmetric groups offers a method to
define nice bases for functions on equivalence classes of permutations.
These bases are useful in counting gauge invariant functions of
matrices or tensors, as well as computing their correlators in physical
theories. In AdS/CFT these bases have proved useful in identifying
local operators in gauge-theory dual to giant gravitons in AdS.
In the simplest cases of gauge-string duality, the known mathematics
of branched covers and Hurwitz spaces provide the mechanism for the
holographic correspondence between gauge invariants and stringy geometry.
(Lecture 2: Local gauge invariant operators and Hilbert space of CFTs. Young diagrams and Brane geometries. Half-BPS and quarter-BPS. Counting, construction and correlators in group theoretic combinatorics.)
Posted by: QMW
November 2017
Thu
30 Nov 2017
Holographic NJL Interactions
Nick Evans
(U. Southampton)
Abstract:
The NJL model is a classic model of chiral symmetry breaking in QCD and the gauged NJL model underlies many BSM models. I investigate how to apply Witten's double trace prescription in holographic models of quarks to describe NJL interactions. A holographic realisation of NJL and gauged NJL is realised and can be applied to understanding QCD and extended technicolor models.
The NJL model is a classic model of chiral symmetry breaking in QCD and the gauged NJL model underlies many BSM models. I investigate how to apply Witten's double trace prescription in holographic models of quarks to describe NJL interactions. A holographic realisation of NJL and gauged NJL is realised and can be applied to understanding QCD and extended technicolor models.
Posted by: QMW
Wed
29 Nov 2017
The classical double copy
📍 London
Christopher White
(QMUL)
Abstract:
Non-abelian gauge theories underlie particle physics, including collision processes at particle accelerators. Recently, quantum scattering probabilities in gauge theories have been shown to be closely related to their counterparts in gravity theories, by the so-called double copy. This suggests a deep relationship between two very different areas of physics, and may lead to new insights into quantum gravity, as well as novel computational methods. This talk will review the double copy for amplitudes, before discussing how it may be extended to describe exact classical solutions such as black holes. Finally, I will discuss hints that the double copy may extend beyond perturbation theory.
Non-abelian gauge theories underlie particle physics, including collision processes at particle accelerators. Recently, quantum scattering probabilities in gauge theories have been shown to be closely related to their counterparts in gravity theories, by the so-called double copy. This suggests a deep relationship between two very different areas of physics, and may lead to new insights into quantum gravity, as well as novel computational methods. This talk will review the double copy for amplitudes, before discussing how it may be extended to describe exact classical solutions such as black holes. Finally, I will discuss hints that the double copy may extend beyond perturbation theory.
Posted by: KCL
Wed
29 Nov 2017
RG flows in 3d N=4 gauge theories
Benjamin Assel
(CERN)
Abstract:
I will present a new approach to study the RG flow in 3d N=4 gauge theories, based on an analysis of the Coulomb branch of vacua. The Coulomb branch is described as a complex algebraic variety and important information about the strongly coupled fixed points of the theory can be extracted from the study of its singularities. I will use this framework to study the fixed points of USp(2N) gauge theories with fundamental matter, revealing some surprising features at low amount of matter.
I will present a new approach to study the RG flow in 3d N=4 gauge theories, based on an analysis of the Coulomb branch of vacua. The Coulomb branch is described as a complex algebraic variety and important information about the strongly coupled fixed points of the theory can be extracted from the study of its singularities. I will use this framework to study the fixed points of USp(2N) gauge theories with fundamental matter, revealing some surprising features at low amount of matter.
Posted by: IC
Fri
24 Nov 2017
Graduate Mini-course: Holographic combinatorics : 2d Yang Mills theory to tensor models via AdS/CFT
Sanjaye Ramgoolam
(QMUL)
Abstract:
These lectures will be focused on aspects of combinatorics relevant to gauge-string duality (holography).
The physical theories we will discuss include two dimensional Yang Mills
theory, N=4 super Yang Mills
theory with U(N) gauge group, Matrix and tensor models.
The key mathematical concepts include : Schur Weyl-duality,
permutation equivalence classes and associated discrete Fourier
transforms as an approach to counting problems and, branched covers and
Hurwitz spaces. Schur-Weyl duality is a powerful relation between
representations of U(N) and representations of symmetric groups.
Representation theory of symmetric groups offers a method to
define nice bases for functions on equivalence classes of permutations.
These bases are useful in counting gauge invariant functions of
matrices or tensors, as well as computing their correlators in physical
theories. In AdS/CFT these bases have proved useful in identifying
local operators in gauge-theory dual to giant gravitons in AdS.
In the simplest cases of gauge-string duality, the known mathematics
of branched covers and Hurwitz spaces provide the mechanism for the
holographic correspondence between gauge invariants and stringy geometry.
(Lecture 1: Two dimensional Yang Mills theory. Exact solution. Large N expansion. Role of Schur-Weyl duality - relation between representation theory of symmetric groups and unitary groups. Hurwitz spaces and string interpretation of the large N expansion.)
These lectures will be focused on aspects of combinatorics relevant to gauge-string duality (holography).
The physical theories we will discuss include two dimensional Yang Mills
theory, N=4 super Yang Mills
theory with U(N) gauge group, Matrix and tensor models.
The key mathematical concepts include : Schur Weyl-duality,
permutation equivalence classes and associated discrete Fourier
transforms as an approach to counting problems and, branched covers and
Hurwitz spaces. Schur-Weyl duality is a powerful relation between
representations of U(N) and representations of symmetric groups.
Representation theory of symmetric groups offers a method to
define nice bases for functions on equivalence classes of permutations.
These bases are useful in counting gauge invariant functions of
matrices or tensors, as well as computing their correlators in physical
theories. In AdS/CFT these bases have proved useful in identifying
local operators in gauge-theory dual to giant gravitons in AdS.
In the simplest cases of gauge-string duality, the known mathematics
of branched covers and Hurwitz spaces provide the mechanism for the
holographic correspondence between gauge invariants and stringy geometry.
(Lecture 1: Two dimensional Yang Mills theory. Exact solution. Large N expansion. Role of Schur-Weyl duality - relation between representation theory of symmetric groups and unitary groups. Hurwitz spaces and string interpretation of the large N expansion.)
Posted by: QMW
Fri
24 Nov 2017
King's Journal Club
📍 London
Cristian Vergu
(KCL)
Abstract:
Discussion of "A spacetime derivation of the Lorentzian OPE inversion formula†by Simmons-Duffin, Stanford and Witten. [1711.03816]
Discussion of "A spacetime derivation of the Lorentzian OPE inversion formula†by Simmons-Duffin, Stanford and Witten. [1711.03816]
Posted by: KCL
Thu
23 Nov 2017
Covariant fuzzy spaces, matrix models and higher spin
Marcus Sperling
(Vienna u.)
Abstract:
In this talk, I will discuss the generalised and basic fuzzy 4-sphere in the context of the IKKT matrix model. These spaces arise as SO(5)-equivariant projections of quantised SO(6) coadjoint orbits and exhibit full SO(5) covariance. I will sketch how (basic and generalised) 4-sphere arise as solutions in a Yang-Mills matrix model, such that the fluctuations on the 4-sphere lead to a higher-spin gauge theory.
In this talk, I will discuss the generalised and basic fuzzy 4-sphere in the context of the IKKT matrix model. These spaces arise as SO(5)-equivariant projections of quantised SO(6) coadjoint orbits and exhibit full SO(5) covariance. I will sketch how (basic and generalised) 4-sphere arise as solutions in a Yang-Mills matrix model, such that the fluctuations on the 4-sphere lead to a higher-spin gauge theory.
Posted by: QMW
Wed
22 Nov 2017
Expanding the Bethe/Gauge Dictionary
📍 London
Tomasz Lukowski
(Oxford)
Abstract:
In this talk I will present recent results on the Bethe/Gauge correspondence obtained together with Mathew Bullimore and Hee-Cheol Kim. I will describe new ingredients of the Bethe/Gauge dictionary between the XXX Heisenberg spin chain and 2d N = (2,2) supersymmetric gauge theories. In particular, I will show how to construct off-shell Bethe states as orbifold defects in the A-twisted supersymmetric gauge theory and study their correlation functions. It will allow us to include aspects of algebraic Bethe ansatz in the correspondence. In particular, I will show how to interpret spin chain R-matrices as correlation functions of Janus interfaces for mass parameters.
In this talk I will present recent results on the Bethe/Gauge correspondence obtained together with Mathew Bullimore and Hee-Cheol Kim. I will describe new ingredients of the Bethe/Gauge dictionary between the XXX Heisenberg spin chain and 2d N = (2,2) supersymmetric gauge theories. In particular, I will show how to construct off-shell Bethe states as orbifold defects in the A-twisted supersymmetric gauge theory and study their correlation functions. It will allow us to include aspects of algebraic Bethe ansatz in the correspondence. In particular, I will show how to interpret spin chain R-matrices as correlation functions of Janus interfaces for mass parameters.
Posted by: KCL
Tue
21 Nov 2017
Breaking integrability at the boundary
Patrick Dorey
(Durham)
Abstract:
This talk will describe some work on the bouncing of particle-like (“kinkâ€) solutions to a nonlinear wave equation, called the sine-Gordon equation, against a fixed boundary. Away from the boundary, this equation has a property known as integrability, making the scattering of the kinks particularly simple. However, if this integrability is broken at the boundary, then the scattering becomes surprisingly complicated, in ways that will be outlined in the talk with the help of some movies.
This talk will describe some work on the bouncing of particle-like (“kinkâ€) solutions to a nonlinear wave equation, called the sine-Gordon equation, against a fixed boundary. Away from the boundary, this equation has a property known as integrability, making the scattering of the kinks particularly simple. However, if this integrability is broken at the boundary, then the scattering becomes surprisingly complicated, in ways that will be outlined in the talk with the help of some movies.
Posted by: CityU2
Fri
17 Nov 2017
King's Journal Club
📍 London
Alejandro Cabo Bizet
(KCL)
Abstract:
Discuss 1710.09580
Discuss 1710.09580
Posted by: KCL
Thu
16 Nov 2017
Quantum Gravity from Conformal Field Theory
James Drummond
(U. Southampton)
Abstract:
I will describe how to recast perturbative quantumgravity using non-perturbative techniques from conformal field theory,focussing on the case of N=4 super Yang-Mills theory. By resolving thedegeneracy among double trace operators at large N we are able to bootstrapone-loop supergravity corrections from the OPE of the CFT.
I will describe how to recast perturbative quantumgravity using non-perturbative techniques from conformal field theory,focussing on the case of N=4 super Yang-Mills theory. By resolving thedegeneracy among double trace operators at large N we are able to bootstrapone-loop supergravity corrections from the OPE of the CFT.
Posted by: QMW
Wed
15 Nov 2017
Black Hole Microstates in String Theory
📍 London
David Turton
(Southampton University)
Abstract:
The Information Paradox represents a strong consistency challenge for any quantum theory of gravity. The study of black hole internal structure in String Theory offers the potential to resolve this paradox. I will give an overview of recent work on constructing families of smooth horizonless supergravity solutions describing black hole microstates. Where applicable, I will present a holographic description of these solutions. I will also discuss the physics of an observer falling into a black hole.
The Information Paradox represents a strong consistency challenge for any quantum theory of gravity. The study of black hole internal structure in String Theory offers the potential to resolve this paradox. I will give an overview of recent work on constructing families of smooth horizonless supergravity solutions describing black hole microstates. Where applicable, I will present a holographic description of these solutions. I will also discuss the physics of an observer falling into a black hole.
Posted by: KCL
Wed
15 Nov 2017
Polygon Seminar: Dualities in d=2+1 Dimensions
David Tong
(DAMTP)
Abstract:
I'll give a basic introduction to particle-vortex duality in d=2+1 dimensions and its relation to 3d bosonization.
I'll give a basic introduction to particle-vortex duality in d=2+1 dimensions and its relation to 3d bosonization.
Posted by: QMW
Tue
14 Nov 2017
Aspects of eta and lambda models and generalised T-duality
Daniel Thompson
(Swansea U.)
Abstract:
In this talk I shall give a review of two classes of integrable non-linear sigma models called \eta and \lambda deformations. Three reasons to be interested are 1) these are interesting examples of relatively rare integrable QFT displaying quantum group symmetries; 2) viewed as string theory sigma models they may have application to N=4 SYM via holography and 3) they provide concrete examples for generalised notions of T-duality. This talk will describe a variety of classical and quantum properties of these theories and their multi-parameter extensions drawing in part on arXiv:1711.00084; arXiv:1706.05322
In this talk I shall give a review of two classes of integrable non-linear sigma models called \eta and \lambda deformations. Three reasons to be interested are 1) these are interesting examples of relatively rare integrable QFT displaying quantum group symmetries; 2) viewed as string theory sigma models they may have application to N=4 SYM via holography and 3) they provide concrete examples for generalised notions of T-duality. This talk will describe a variety of classical and quantum properties of these theories and their multi-parameter extensions drawing in part on arXiv:1711.00084; arXiv:1706.05322
Posted by: QMW
Thu
9 Nov 2017
Integrable lattice models in the UV
Luigi Tizzano
(Uppsala U.)
Abstract:
Integrable lattice models in 1+1 dimensions have been a topic of much fascination in physics since the early days of quantum mechanics. Recently, a work by Costello has offered a new perspective on these models based on a 4D topological gauge theory. An interesting aspect of this proposal is the close connection with 3D Chern-Simons theory and knot invariants. I will explain how to derive the 4D topological theory using string dualities and localization techniques for a 5D twisted super Yang-Mills theory. Finally, I will explain how this construction might relate to other appearances of Yangian symmetry which played a prominent role in AdS/CFT physics. This is a joint work in progress with Joe Minahan.
Integrable lattice models in 1+1 dimensions have been a topic of much fascination in physics since the early days of quantum mechanics. Recently, a work by Costello has offered a new perspective on these models based on a 4D topological gauge theory. An interesting aspect of this proposal is the close connection with 3D Chern-Simons theory and knot invariants. I will explain how to derive the 4D topological theory using string dualities and localization techniques for a 5D twisted super Yang-Mills theory. Finally, I will explain how this construction might relate to other appearances of Yangian symmetry which played a prominent role in AdS/CFT physics. This is a joint work in progress with Joe Minahan.
Posted by: QMW
Wed
8 Nov 2017
Twisted BRST quantization and localization in supergravity
📍 London
Sameer Murthy
(King's College London)
Abstract:
Supersymmetric localization is a powerful technique to evaluate a class of functional integrals in supersymmetric field theories. It reduces the functional integral over field space to ordinary integrals over the space of solutions of the off-shell BPS equations. The application of this technique to supergravity suffers from some problems, both conceptual and practical. I will discuss one of the main conceptual problems, namely how to construct the fermionic symmetry with which to localize. I will show how a deformation of the BRST technique allows us to do this. I will then sketch a computation of the one-loop determinant of the super-graviton that enters the localization formula for BPS black hole entropy.
Supersymmetric localization is a powerful technique to evaluate a class of functional integrals in supersymmetric field theories. It reduces the functional integral over field space to ordinary integrals over the space of solutions of the off-shell BPS equations. The application of this technique to supergravity suffers from some problems, both conceptual and practical. I will discuss one of the main conceptual problems, namely how to construct the fermionic symmetry with which to localize. I will show how a deformation of the BRST technique allows us to do this. I will then sketch a computation of the one-loop determinant of the super-graviton that enters the localization formula for BPS black hole entropy.
Posted by: KCL
Wed
8 Nov 2017
RG Flows Across Dimensions and Holography
Nikolay Bobev
(KU Leuven)
Abstract:
Superconformal field theories placed in nontrivial background fields for the metric and the continuous global symmetries exhibit a rich web of RG flows across dimensions. I will discuss several examples of such flows and emphasize some of their universal features. In addition, I will employ non-perturbative tools such as 't Hooft anomaly matching, a-, F-, and c-extremization, and holography to gain a quantitative understanding of some aspects of these theories. Finally, I will discuss the relevance of these results for a microscopic understanding of the entropy of supersymmetric black holes and strings in AdS.
Superconformal field theories placed in nontrivial background fields for the metric and the continuous global symmetries exhibit a rich web of RG flows across dimensions. I will discuss several examples of such flows and emphasize some of their universal features. In addition, I will employ non-perturbative tools such as 't Hooft anomaly matching, a-, F-, and c-extremization, and holography to gain a quantitative understanding of some aspects of these theories. Finally, I will discuss the relevance of these results for a microscopic understanding of the entropy of supersymmetric black holes and strings in AdS.
Posted by: IC
Fri
3 Nov 2017
King's Journal Club
📍 London
Chris Couzens
(King's College)
Abstract:
Review of 1710.03934v1
Review of 1710.03934v1
Posted by: KCL
Wed
1 Nov 2017
Triangle Seminar: The S-matrix bootstrap - old and new
Balt Van Rees
Abstract:
From a modern viewpoint the "S-matrix bootstrap" is the idea that general consistency conditions can be used to obtain quantitative constraints on scattering amplitudes. I will discuss the assumptions behind this approach, open questions about the structure of amplitudes, and discuss some fundamental results from the sixties and seventies. In the second part of the talk I will treat two modern approaches which were inspired by recent results on the conformal bootstrap, and show how they can be used to constrain scattering amplitudes in non-trivial ways.
From a modern viewpoint the "S-matrix bootstrap" is the idea that general consistency conditions can be used to obtain quantitative constraints on scattering amplitudes. I will discuss the assumptions behind this approach, open questions about the structure of amplitudes, and discuss some fundamental results from the sixties and seventies. In the second part of the talk I will treat two modern approaches which were inspired by recent results on the conformal bootstrap, and show how they can be used to constrain scattering amplitudes in non-trivial ways.
Posted by: IC
October 2017
Fri
27 Oct 2017
King's Journal Club
📍 London
Rajesh Gupta
(KCL)
Abstract:
We will discuss "From 3d duality to 2d duality" https://arxiv.org/abs/1710.00926 by Aharony, Razamat and Willett.
We will discuss "From 3d duality to 2d duality" https://arxiv.org/abs/1710.00926 by Aharony, Razamat and Willett.
Posted by: KCL
Wed
25 Oct 2017
Chiral Algebras for four dimensional N=4 SCFT
📍 London
Carlo Meneghelli
(Oxford)
Abstract:
Any four dimensional N=2 superconformal field theory (SCFT) contains a subsector of local operator which is isomorphic to a two dimensional chiral algebra. If the 4d theory possesses N=3 or N= 4 superconformal symmetry, the corresponding chiral algebra is an extension the N=2 or (small) N=4 super-Virasoro algebra respectively. In this talk I will present some results on the classification of N=4 chiral algebras and discuss if they can correspond to a 4d theory.
Any four dimensional N=2 superconformal field theory (SCFT) contains a subsector of local operator which is isomorphic to a two dimensional chiral algebra. If the 4d theory possesses N=3 or N= 4 superconformal symmetry, the corresponding chiral algebra is an extension the N=2 or (small) N=4 super-Virasoro algebra respectively. In this talk I will present some results on the classification of N=4 chiral algebras and discuss if they can correspond to a 4d theory.
Posted by: KCL
Wed
25 Oct 2017
Current Algebra and CFTs at Null Infinity from Amplitudes
Dhritiman Nandan
(Edinburgh)
Abstract:
We describe the leading and sub-leading multi-soft behavior of tree level gluon amplitudes and an underlying two-dimensional description of such scenarios where the soft limits are currents related to asymptotic symmetries of YM theory. Such kinematic limits allow us to explore the algebra of these two dimensional currents and we comment on their CFT interpretation. Then we explore a possible two-dimensional description of certain amplitudes in massive scalar QFT’s.
We describe the leading and sub-leading multi-soft behavior of tree level gluon amplitudes and an underlying two-dimensional description of such scenarios where the soft limits are currents related to asymptotic symmetries of YM theory. Such kinematic limits allow us to explore the algebra of these two dimensional currents and we comment on their CFT interpretation. Then we explore a possible two-dimensional description of certain amplitudes in massive scalar QFT’s.
Posted by: IC
Tue
24 Oct 2017
Large Conformal Goldstone Mode Fluctuations in the SYK Model
Alexander Altland
(Koeln)
Abstract:
This talk addresses the low energy physics of the Sachdev-Ye-Kitaev model, a paradigm of strongly interacting (Majorana) quantum matter. A salient feature of this system is its exceptionally high degree of symmetry under reparameterizations of physical time. At low energies this symmetry is spontaneously broken and the ensuing infinite dimensional Goldstone mode manifold takes strong influence on all physical observables. We will discuss the effects of these fluctuations on the example of the so-called out of time ordered correlation functions, diagnostic tools to describe both manifestations of quantum chaos in the system and its conjectured duality to an AdS2 gravitational bulk. While previous work predicts exponential decay of these correlations in time our main finding is that at large time scales non-perturbative Goldstone mode fluctuations generate a crossover to power law behavior. This phenomenon must have ramifications in the physics of the holographic bulk which, however, we do not understand at present.
This talk addresses the low energy physics of the Sachdev-Ye-Kitaev model, a paradigm of strongly interacting (Majorana) quantum matter. A salient feature of this system is its exceptionally high degree of symmetry under reparameterizations of physical time. At low energies this symmetry is spontaneously broken and the ensuing infinite dimensional Goldstone mode manifold takes strong influence on all physical observables. We will discuss the effects of these fluctuations on the example of the so-called out of time ordered correlation functions, diagnostic tools to describe both manifestations of quantum chaos in the system and its conjectured duality to an AdS2 gravitational bulk. While previous work predicts exponential decay of these correlations in time our main finding is that at large time scales non-perturbative Goldstone mode fluctuations generate a crossover to power law behavior. This phenomenon must have ramifications in the physics of the holographic bulk which, however, we do not understand at present.
Posted by: CityU2
Thu
19 Oct 2017
AdS3/CFT_2 and F-Theory
Christopher Couzens
(King's Coll. London)
Abstract:
In this talk we consider holographic duals of F-theory solutions to 2d SCFT's. We approach the problem by classifying a particular class of solutions of type IIB supergravity with AdS_3 factors and varying axio-dilaton. The class of solutions we discuss consist of D3 and 7-brane configurations and naturally fall into the realm of F-theory. We prove that for (0,4) supersymmetry in 2d the solutions are essentially unique and we match the holographic central charges to field theory results. We comment on future directions, including AdS_3 solutions of F-theory, preserving different amounts of supersymmetry.
In this talk we consider holographic duals of F-theory solutions to 2d SCFT's. We approach the problem by classifying a particular class of solutions of type IIB supergravity with AdS_3 factors and varying axio-dilaton. The class of solutions we discuss consist of D3 and 7-brane configurations and naturally fall into the realm of F-theory. We prove that for (0,4) supersymmetry in 2d the solutions are essentially unique and we match the holographic central charges to field theory results. We comment on future directions, including AdS_3 solutions of F-theory, preserving different amounts of supersymmetry.
Posted by: QMW
Wed
18 Oct 2017
On the exact interpolating function in ABJ theory
📍 London
Andrea Cavaglia
(KCL)
Abstract:
I will discuss integrability in the context of planar AdS4/CFT3,
where the CFT is the so-called ABJ model depending on two t'Hooft couplings.
When the two couplings are equal, this reduces to the ABJM theory, whose integrable structure is well understood
but depends on an unspecified interpolating function of the coupling.
I will motivate a proposal that the most general ABJ case is also integrable,
and that the two coupling constants l1 and l2 recombine into a single
interpolating function h( l1 , l2 ) , so that the spectrum is a function of h only.
Extending and idea by N. Gromov and G. Sizov on the ABJM case,
an explicit conjecture for the form of h(l1, l2) wil be made, based on the comparison between
integrability and localization results.
The talk is based on the paper hep-th/1605.04888 with N. Gromov and F. Levkovich-Maslyuk.
I will discuss integrability in the context of planar AdS4/CFT3,
where the CFT is the so-called ABJ model depending on two t'Hooft couplings.
When the two couplings are equal, this reduces to the ABJM theory, whose integrable structure is well understood
but depends on an unspecified interpolating function of the coupling.
I will motivate a proposal that the most general ABJ case is also integrable,
and that the two coupling constants l1 and l2 recombine into a single
interpolating function h( l1 , l2 ) , so that the spectrum is a function of h only.
Extending and idea by N. Gromov and G. Sizov on the ABJM case,
an explicit conjecture for the form of h(l1, l2) wil be made, based on the comparison between
integrability and localization results.
The talk is based on the paper hep-th/1605.04888 with N. Gromov and F. Levkovich-Maslyuk.
Posted by: KCL
Tue
17 Oct 2017
Renormalization of total sets of states into generalized bases with a resolution of the identity: a cooperative game theory approach
Apostolos Vourdas
(Bradford)
Abstract:
A total set of states for which we have no resolution of the identity (a 'pre-basis'), is considered
in a finite dimensional Hilbert space. A dressing formalism renormalizes them into density matrices
which resolve the identity, and makes them a 'generalized basis', which is practically useful. The
dresssing mechanism is inspired by Shapley's methodology in cooperative game theory, and it uses
Moebius transforms. There is non-independence and redundancy in these generalized bases, which is
quantified with a Shannon type of entropy. Due to this redundancy, calculations based on generalized
bases, are sensitive to physical changes and robust in the presence of noise. For example, the
representation of an arbitrary vector in such generalized bases, is robust when noise is inserted in
the coefficients. Also in a physical system with ground state which changes abruptly at some value
of the coupling constant, the proposed methodology detects such changes, even when noise is added
to the parameters in the Hamiltonian of the system.
A total set of states for which we have no resolution of the identity (a 'pre-basis'), is considered
in a finite dimensional Hilbert space. A dressing formalism renormalizes them into density matrices
which resolve the identity, and makes them a 'generalized basis', which is practically useful. The
dresssing mechanism is inspired by Shapley's methodology in cooperative game theory, and it uses
Moebius transforms. There is non-independence and redundancy in these generalized bases, which is
quantified with a Shannon type of entropy. Due to this redundancy, calculations based on generalized
bases, are sensitive to physical changes and robust in the presence of noise. For example, the
representation of an arbitrary vector in such generalized bases, is robust when noise is inserted in
the coefficients. Also in a physical system with ground state which changes abruptly at some value
of the coupling constant, the proposed methodology detects such changes, even when noise is added
to the parameters in the Hamiltonian of the system.
Posted by: KCL
Wed
11 Oct 2017
Polygon Seminar
TBA TBA
(TBA)
Tue
10 Oct 2017
Brane sigma models and solutions in M, Mstar, and Mprime theories
Sarben Sarkar
(King's)
Abstract:
I discuss one and two-parameter solutions of sigma models on
symmetric spaces contained in E11. Embedding one-parameter
sigma model solutions in space-time give a metric which
depends on harmonic functions typical in general relativity,
supergravity and M-theory. Embedding two-parameter sigma
model solutions in space-time give a metric which depends on
general travelling wave functions in M* and M’-theory
(theories which have space-time signatures with more than
one time). Weyl reflection allows the latter solutions to be
mapped to M-theory solutions where the wave functions
depend explicitly on extra co-ordinates contained in the
fundamental representation of E11. I will also give an example of two-time physics realisable in the laboratory
I discuss one and two-parameter solutions of sigma models on
symmetric spaces contained in E11. Embedding one-parameter
sigma model solutions in space-time give a metric which
depends on harmonic functions typical in general relativity,
supergravity and M-theory. Embedding two-parameter sigma
model solutions in space-time give a metric which depends on
general travelling wave functions in M* and M’-theory
(theories which have space-time signatures with more than
one time). Weyl reflection allows the latter solutions to be
mapped to M-theory solutions where the wave functions
depend explicitly on extra co-ordinates contained in the
fundamental representation of E11. I will also give an example of two-time physics realisable in the laboratory
Posted by: CityU2
Thu
5 Oct 2017
On self-dual N=4 theories
Inaki Garcia Etxebarria
(MPI Munich)
Wed
4 Oct 2017
The topologically twisted index on H2xS1 and its relation to the entropy of hyperbolic AdS4 black holes.
📍 London
Alejandro Cabo-Bizet
(KCL)
Abstract:
I will start by sketching the computation of the topologically
twisted index on H2xS1 and its evaluation in ABJM theory in the large N
limit with k=1.
Then after, I will review the key points behind the construction of
magnetically charged (hyperbolic) AdS4 black holes on STU gauged SUGRA and
will conclude by stating how the aformentioned index – upon extremization
– coincides with the entropy of the latter black holes in the large N
limit (with k=1).
I will start by sketching the computation of the topologically
twisted index on H2xS1 and its evaluation in ABJM theory in the large N
limit with k=1.
Then after, I will review the key points behind the construction of
magnetically charged (hyperbolic) AdS4 black holes on STU gauged SUGRA and
will conclude by stating how the aformentioned index – upon extremization
– coincides with the entropy of the latter black holes in the large N
limit (with k=1).
Posted by: KCL
Wed
4 Oct 2017
TBA
Nabil Iqbal
(Durham)
Tue
3 Oct 2017
Neuro-Topology: An interaction between topology and neuroscience
Ran Levi
(Aberdeen)
Abstract:
While algebraic topology is now well established as an applicable branch of mathematics, its emergence in neuroscience is surprisingly recent. In this talk I will present a summary of an ongoing joint project with mathematician and neuroscientists. I will start with some basic facts on neuroscience and the digital reconstruction of a rat’s neocortex by the Blue Brain Project in EPFL. I will then explain how data emerging from this reconstruction can be mapped into abstract graphs that in turn give rise to certain mathematical objects in the realm of algebraic and combinatorial topology. Following a short introduction to some of the basic tools of algebraic topology, I will explain how they can potentially be used in the context of neuroscience. Having set up the scene, I will proceed by presenting the results of an ongoing collaboration with the Blue Brain Project team. In particular I shall demonstrate how the topological techniques give new insights on the behaviour of neural systems and inspire new directions in neuroscience research.
While algebraic topology is now well established as an applicable branch of mathematics, its emergence in neuroscience is surprisingly recent. In this talk I will present a summary of an ongoing joint project with mathematician and neuroscientists. I will start with some basic facts on neuroscience and the digital reconstruction of a rat’s neocortex by the Blue Brain Project in EPFL. I will then explain how data emerging from this reconstruction can be mapped into abstract graphs that in turn give rise to certain mathematical objects in the realm of algebraic and combinatorial topology. Following a short introduction to some of the basic tools of algebraic topology, I will explain how they can potentially be used in the context of neuroscience. Having set up the scene, I will proceed by presenting the results of an ongoing collaboration with the Blue Brain Project team. In particular I shall demonstrate how the topological techniques give new insights on the behaviour of neural systems and inspire new directions in neuroscience research.
Posted by: CityU2
Mon
2 Oct 2017
AdS3/CFT2 and F-Theory
Christopher Couzens
(King's)
Abstract:
In this talk we consider holographic duals of F-theory solutions to 2d SCFT's. We approach the problem by classifying a particular class of solutions of type IIB supergravity with AdS_3 factors and varying axio-dilaton. The class of solutions we discuss consist of D3 and 7-brane configurations and naturally fall into the realm of F-theory. We prove that for (0,4) supersymmetry in 2d the solutions are essentially unique and we match the holographic central charges to field theory results. We comment on future directions, including AdS_3 solutions of F-theory, preserving different amounts of supersymmetry.
In this talk we consider holographic duals of F-theory solutions to 2d SCFT's. We approach the problem by classifying a particular class of solutions of type IIB supergravity with AdS_3 factors and varying axio-dilaton. The class of solutions we discuss consist of D3 and 7-brane configurations and naturally fall into the realm of F-theory. We prove that for (0,4) supersymmetry in 2d the solutions are essentially unique and we match the holographic central charges to field theory results. We comment on future directions, including AdS_3 solutions of F-theory, preserving different amounts of supersymmetry.
Posted by: CityU2
September 2017
Wed
27 Sep 2017
Segmented strings
📍 London
David Vegh
(QMUL)
Abstract:
The goal of this talk is twofold. Firstly, I would like to popularize the segmented string approach for solving the classical string dynamics on certain symmetric spacetimes where the string motion is integrable. This allows for an exact discretization which renders the equation of motion discrete in both space and time. The corresponding string solution is a segmented string. I will review the properties of segmented strings and relate them to discrete-time Toda-type lattices.
The second goal of the talk is to understand a concrete setup: a (segmented) string hanging from the boundary of three-dimensional AdS spacetime. According to the gauge/gravity duality, the string in the bulk is dual to a flux tube between a quark-antiquark pair in the boundary field theory. We assume that the string is initially (quasi-)static. Perturbing one of the endpoints creates a large propagating wave on the string. The non-linear time-evolution produces a number of interesting phenomena: energy cascades, pair-creation of cusps, and evaporating regions on the string.
If time permits, I will also talk about the string worldsheet as a simple model for gravity, chaos, out-of-time-order four-point functions, and segmented membranes.
The goal of this talk is twofold. Firstly, I would like to popularize the segmented string approach for solving the classical string dynamics on certain symmetric spacetimes where the string motion is integrable. This allows for an exact discretization which renders the equation of motion discrete in both space and time. The corresponding string solution is a segmented string. I will review the properties of segmented strings and relate them to discrete-time Toda-type lattices.
The second goal of the talk is to understand a concrete setup: a (segmented) string hanging from the boundary of three-dimensional AdS spacetime. According to the gauge/gravity duality, the string in the bulk is dual to a flux tube between a quark-antiquark pair in the boundary field theory. We assume that the string is initially (quasi-)static. Perturbing one of the endpoints creates a large propagating wave on the string. The non-linear time-evolution produces a number of interesting phenomena: energy cascades, pair-creation of cusps, and evaporating regions on the string.
If time permits, I will also talk about the string worldsheet as a simple model for gravity, chaos, out-of-time-order four-point functions, and segmented membranes.
Posted by: KCL
Wed
27 Sep 2017
TBA
Antoine Bourget
(Oviedo)
Wed
20 Sep 2017
Alternative boundary conditions in AdS, one-loop determinants and WCFTs
Phil Szepietowski
(Utrecht)
Abstract:
I will discuss the computation of the graviton one-loop determinant in the BTZ black hole background with certain chiral boundary conditions at the AdS boundary. These boundary conditions were proposed by Compere, Song and Strominger and were shown to modify the asymptotic symmetry algebra from a sum of left and right Virasoro algebras to a single right-moving Virasoro U(1) Kac-Moody. This implies that the holographic dual description possesses such global symmetry and so should be described by a warped conformal field theory (WCFT) instead of a standard CFT. In the talk I will overview the new boundary conditions and the concept of a WCFT, outline the computational method of obtaining the one-loop determinant from the "quasinormal" mode spectrum (highlighting elements which are unique to the new boundary conditions) and discuss the implications of the results for the boundary field theory.
I will discuss the computation of the graviton one-loop determinant in the BTZ black hole background with certain chiral boundary conditions at the AdS boundary. These boundary conditions were proposed by Compere, Song and Strominger and were shown to modify the asymptotic symmetry algebra from a sum of left and right Virasoro algebras to a single right-moving Virasoro U(1) Kac-Moody. This implies that the holographic dual description possesses such global symmetry and so should be described by a warped conformal field theory (WCFT) instead of a standard CFT. In the talk I will overview the new boundary conditions and the concept of a WCFT, outline the computational method of obtaining the one-loop determinant from the "quasinormal" mode spectrum (highlighting elements which are unique to the new boundary conditions) and discuss the implications of the results for the boundary field theory.
Posted by: IC
Thu
14 Sep 2017
The decay width of stringy hadrons
Jacob Sonnenschein
(Tel Aviv University)
Abstract:
I will start with briefly describing the HISH ( Holography In- spired Hadronic String) model and reviewing the fits of the spectra of mesons, baryons, glueballs and exotic hadrons.
I will present the determination of the hadron strong decay widths. The
main decay mechanism is that of a string splitting into two strings. The
corresponding total decay width behaves as Γ = πATL/2 where T and L
are the tension and length of the string and A is a dimensionless universal constant. The partial width of a given decay mode is given by Γ_i/Γ = Φ_i exp(−2Ï€Cm^2_sep/T) where Φi is a phase space factor, msep is the mass of the â€quark†and â€antiquark†created at the splitting point, and C is a dimensionless coefficient close to unity.
I will show the fits of the theoretical results to experimental data for mesons and baryons. I will examine both the linearity in L and the expo- nential suppression factor. The linearity was found to agree with the data well for mesons but less for baryons. The extracted coefficient for mesons A = 0.095 ± 0.015 is indeed quite universal. The exponential suppression was applied to both strong and radiative decays. I will discuss the relation with string fragmentation and jet formation. I will extract the quark-diquark structure of baryons from their decays. A stringy mechanism for Zweig sup- pressed decays of quarkonia will be proposed and will be shown to reproduce the decay width of Υ states. The dependence of the width on spin and flavor symmetry will be discussed. We further apply this model to the decays of glueballs and exotic hadrons.
I will start with briefly describing the HISH ( Holography In- spired Hadronic String) model and reviewing the fits of the spectra of mesons, baryons, glueballs and exotic hadrons.
I will present the determination of the hadron strong decay widths. The
main decay mechanism is that of a string splitting into two strings. The
corresponding total decay width behaves as Γ = πATL/2 where T and L
are the tension and length of the string and A is a dimensionless universal constant. The partial width of a given decay mode is given by Γ_i/Γ = Φ_i exp(−2Ï€Cm^2_sep/T) where Φi is a phase space factor, msep is the mass of the â€quark†and â€antiquark†created at the splitting point, and C is a dimensionless coefficient close to unity.
I will show the fits of the theoretical results to experimental data for mesons and baryons. I will examine both the linearity in L and the expo- nential suppression factor. The linearity was found to agree with the data well for mesons but less for baryons. The extracted coefficient for mesons A = 0.095 ± 0.015 is indeed quite universal. The exponential suppression was applied to both strong and radiative decays. I will discuss the relation with string fragmentation and jet formation. I will extract the quark-diquark structure of baryons from their decays. A stringy mechanism for Zweig sup- pressed decays of quarkonia will be proposed and will be shown to reproduce the decay width of Υ states. The dependence of the width on spin and flavor symmetry will be discussed. We further apply this model to the decays of glueballs and exotic hadrons.
Posted by: IC
Wed
13 Sep 2017
Higher-loop amplitude monodromy relations in string and gauge theory
Piotr Tourkine
(DAMTP)
Abstract:
The monodromy relations of scattering amplitudes in string theory provide an elegant formalism to understand some mysterious properties of tree-level field theory amplitudes, like the color-kinematics duality. This duality has been instrumental in tremendous progress on the computations of loop-amplitudes in quantum field theory, but a loop-level generalisation of the stringy monodromy construction has been lacking for many years.
In this talk I will first describe some of these recent developments in the domain of scattering amplitudes in gauge and gravity theories.
I’ll then review the monodromies of open string worldsheets and how the lead at tree-level to deepening the understanding of the gauge theory perturbative expansion.
Then I will describe in a non-technical manner our results and how we managed to extend these relations to all loops in string and field theory. I’ll finish by discussing implications for the loop expansion in general, and how to extend in principle these results to gravity.
I will assume no prior knowledge of the audience in modern scattering amplitudes methods.
The monodromy relations of scattering amplitudes in string theory provide an elegant formalism to understand some mysterious properties of tree-level field theory amplitudes, like the color-kinematics duality. This duality has been instrumental in tremendous progress on the computations of loop-amplitudes in quantum field theory, but a loop-level generalisation of the stringy monodromy construction has been lacking for many years.
In this talk I will first describe some of these recent developments in the domain of scattering amplitudes in gauge and gravity theories.
I’ll then review the monodromies of open string worldsheets and how the lead at tree-level to deepening the understanding of the gauge theory perturbative expansion.
Then I will describe in a non-technical manner our results and how we managed to extend these relations to all loops in string and field theory. I’ll finish by discussing implications for the loop expansion in general, and how to extend in principle these results to gravity.
I will assume no prior knowledge of the audience in modern scattering amplitudes methods.
Posted by: IC