Triangle Seminars
July 2018
Mon
23 Jul 2018
Einstein Double Field Equations
Jeong-Hyuck Park
(Sogang University)
Abstract:
String theory predicts its own gravity rather than GR. In General Relativity the metric is the only geometric and gravitational field, whereas in string theory the closed-string massless sector comprises a skew-symmetric B-field and the string dilaton in addition to the metric. Furthermore, these three fields transform into each other under T-duality. This hints at a natural augmentation of GR: upon treating the whole closed string massless sector as stringy graviton fields, Double Field Theory may evolve into `Stringy Gravity'. Equipped with an O(D,D) covariant differential geometry beyond Riemann, we spell out the definitions of the stringy Einstein curvature tensor and the stringy Energy-Momentum tensor. Equating them, all the equations of motion of the closed string massless sector are unified into a single expression which we dub the Einstein Double Field Equations.
String theory predicts its own gravity rather than GR. In General Relativity the metric is the only geometric and gravitational field, whereas in string theory the closed-string massless sector comprises a skew-symmetric B-field and the string dilaton in addition to the metric. Furthermore, these three fields transform into each other under T-duality. This hints at a natural augmentation of GR: upon treating the whole closed string massless sector as stringy graviton fields, Double Field Theory may evolve into `Stringy Gravity'. Equipped with an O(D,D) covariant differential geometry beyond Riemann, we spell out the definitions of the stringy Einstein curvature tensor and the stringy Energy-Momentum tensor. Equating them, all the equations of motion of the closed string massless sector are unified into a single expression which we dub the Einstein Double Field Equations.
Posted by: QMW
June 2018
Thu
21 Jun 2018
Submatrix deconfinement and small black holes in AdS
David Berenstein
(UC Santa Barbara)
Thu
7 Jun 2018
Viscoelastic holography: from fluids to solids
Matteo Baggioli
(Crete U.)
Abstract:
A review of the recent progress regarding the holograhic duals for viscoelastic and solid materials.
After introducing a simple bottom-up model able of realizing such a setup the following physical properties will be discussed:
i) the linear elastic features
ii) viscoelasticity
ii) the nature of phonons and pinning
iii) the non linear elastic properties
iiii) the convergence properties of the asymptotic expansion.
A review of the recent progress regarding the holograhic duals for viscoelastic and solid materials.
After introducing a simple bottom-up model able of realizing such a setup the following physical properties will be discussed:
i) the linear elastic features
ii) viscoelasticity
ii) the nature of phonons and pinning
iii) the non linear elastic properties
iiii) the convergence properties of the asymptotic expansion.
Posted by: QMW
May 2018
Thu
31 May 2018
Perfect probabilistic storing and retrieving of unitary channels
Michal Sedlak
(Slovak Academy of Sciences)
Abstract:
Any sequence of quantum gates on a set of qubits defines a multipartite unitary transformation. These sequences may correspond to some parts of a quantum computation or they may be used to encode classical/quantum information (e.g. in private quantum channels). If we have only limited access to such a unitary transformation, we may want to store it into a quantum memory and later perfectly retrieve it. Thus, once we cannot use the unitary transformation directly anymore, we could still apply it to any state with the help of the footprint kept in the quantum memory. This can be useful for speeding up some calculations or as an attack for process based quantum key distribution protocol or a communication scheme. We require the storing and retrieving protocol to perfectly reconstruct the unitary transformation, which implies non unit probability of success. We derive optimal probability of success for a d-dimensional unitary transformation used N-times. The optimal probability of success has a very simple form N/(N-1+d^2). This result implies that reliable storing of d^2 parameters of the unknown unitary transformation requires roughly d^2 uses of the transformation.
Any sequence of quantum gates on a set of qubits defines a multipartite unitary transformation. These sequences may correspond to some parts of a quantum computation or they may be used to encode classical/quantum information (e.g. in private quantum channels). If we have only limited access to such a unitary transformation, we may want to store it into a quantum memory and later perfectly retrieve it. Thus, once we cannot use the unitary transformation directly anymore, we could still apply it to any state with the help of the footprint kept in the quantum memory. This can be useful for speeding up some calculations or as an attack for process based quantum key distribution protocol or a communication scheme. We require the storing and retrieving protocol to perfectly reconstruct the unitary transformation, which implies non unit probability of success. We derive optimal probability of success for a d-dimensional unitary transformation used N-times. The optimal probability of success has a very simple form N/(N-1+d^2). This result implies that reliable storing of d^2 parameters of the unknown unitary transformation requires roughly d^2 uses of the transformation.
Posted by: QMW
Wed
30 May 2018
Exotic Rational CFT and the Modular Bootstrap
Sunil Mukhi
(IISER, Pune)
Abstract:
I will summarise old and recent developments on the classification and solution of Rational Conformal Field Theories in 2 dimensions using the method of Modular Differential Equations. Novel and exotic theories are found with small numbers of characters and simple fusion rules, one of these being the Baby Monster CFT. Correlation functions for many of these theories can be computed using crossing-symmetric differential equations.
I will summarise old and recent developments on the classification and solution of Rational Conformal Field Theories in 2 dimensions using the method of Modular Differential Equations. Novel and exotic theories are found with small numbers of characters and simple fusion rules, one of these being the Baby Monster CFT. Correlation functions for many of these theories can be computed using crossing-symmetric differential equations.
Posted by: QMW
Thu
24 May 2018
Positivity Constraints in Effective Field Theories
Andrew Tolley
(Imperial College London)
Abstract:
I will review how the requirements of unitarity, locality, causality and Lorentz invariance impose constraints on the signs of the operator coefficients in an effective field theory, discuss recent work on generalizing these constraints to arbitrary spin particles, and discuss how these can be used to constrain gravitational EFTs of the type considered by cosmologists as models for dark energy or inflation.
I will review how the requirements of unitarity, locality, causality and Lorentz invariance impose constraints on the signs of the operator coefficients in an effective field theory, discuss recent work on generalizing these constraints to arbitrary spin particles, and discuss how these can be used to constrain gravitational EFTs of the type considered by cosmologists as models for dark energy or inflation.
Posted by: QMW
Thu
17 May 2018
tba
Suresh Nampuri
(Lisbon IST)
Wed
16 May 2018
Exotic Rational CFT and the Modular Bootstrap
📍 London
Sunil Mukhi
(IISER Pune)
Abstract:
I will summarise old and recent developments on the classification and solution of Rational Conformal Field Theories in 2 dimensions using the method of Modular Differential Equations. Novel and exotic theories are found with small numbers of characters and simple fusion rules, one of these being the Baby Monster CFT. Correlation functions for many of these theories can be computed using crossing-symmetric differential equations.
I will summarise old and recent developments on the classification and solution of Rational Conformal Field Theories in 2 dimensions using the method of Modular Differential Equations. Novel and exotic theories are found with small numbers of characters and simple fusion rules, one of these being the Baby Monster CFT. Correlation functions for many of these theories can be computed using crossing-symmetric differential equations.
Posted by: KCL
Thu
10 May 2018
Non-Abelian T-duality in AdS/CFT: the CFT side
Yolanda Lozano
(Oviedo U.)
Abstract:
Non-Abelian T-duality, a transformation in String Theory known since the 90’s, has been shown recently to be a powerful solution generating technique in supergravity. In this talk I will discuss various AdS backgrounds generated through this transformation, for which it is possible to give a dual CFT interpretation arising from Hanany-Witten brane set-ups.
Non-Abelian T-duality, a transformation in String Theory known since the 90’s, has been shown recently to be a powerful solution generating technique in supergravity. In this talk I will discuss various AdS backgrounds generated through this transformation, for which it is possible to give a dual CFT interpretation arising from Hanany-Witten brane set-ups.
Posted by: QMW
Wed
2 May 2018
Losing the IR: A New Framework for Holographic Area Laws
Netta Engelhardt
(Princeton)
Abstract:
I will describe a new procedure for coarse-graining over the gravitational degrees of freedom inside a surface in the context of AdS/CFT. I will prove that in general dimensions, this coarse-graining gives an explanation of an infinite family of gravitational area laws. In three bulk dimensions, it is also straightforward to derive the precise dual of these area laws as strong subadditivity of the von Neuman entropy in the dual CFT. I will discuss a number of implications of this, which include an explanation for the geometric bulk phenomenon of extremal surface barriers
I will describe a new procedure for coarse-graining over the gravitational degrees of freedom inside a surface in the context of AdS/CFT. I will prove that in general dimensions, this coarse-graining gives an explanation of an infinite family of gravitational area laws. In three bulk dimensions, it is also straightforward to derive the precise dual of these area laws as strong subadditivity of the von Neuman entropy in the dual CFT. I will discuss a number of implications of this, which include an explanation for the geometric bulk phenomenon of extremal surface barriers
Posted by: IC
April 2018
Thu
26 Apr 2018
The different guises of elliptic Feynman integrals
Claude Duhr
(Cern)
Abstract:
The computation of Feynman integrals is an important ingredient to compute scattering amplitudes to higher orders in perturbative QFT. Over the last couple of years, a lot of progress was made in understanding the mathematics of multi-loop Feynman integrals. In particular, it was understood that large classes of integrals evaluate to a class of special functions called multiple polylogarithms, which are an object of active research also in pure mathematics. It is known that starting from two loop, generalisations of polylogarithms to elliptic curves can show up. In this talk we review certain classes of elliptic multiple polylogarithms, and we show that they are closely related to iterated integrals on certain modular curves.
The computation of Feynman integrals is an important ingredient to compute scattering amplitudes to higher orders in perturbative QFT. Over the last couple of years, a lot of progress was made in understanding the mathematics of multi-loop Feynman integrals. In particular, it was understood that large classes of integrals evaluate to a class of special functions called multiple polylogarithms, which are an object of active research also in pure mathematics. It is known that starting from two loop, generalisations of polylogarithms to elliptic curves can show up. In this talk we review certain classes of elliptic multiple polylogarithms, and we show that they are closely related to iterated integrals on certain modular curves.
Posted by: QMW
Thu
19 Apr 2018
Cluster algebras, integrability and scattering amplitudes
Georgios Papathanasiou
(DESY)
Abstract:
I present recent progress towards determining the planar S-matrix of maximally supersymmetric Yang-Mills theory, thanks to the rich interplay between its perturbative analytic properties in general kinematics, and its integrable structure in special kinematics. The former are related to cluster algebras, and allow for the computation of amplitudes with six/seven gluons up to six/four loops, whereas the latter yields all amplitudes in the multi-Regge limit at finite coupling.
I present recent progress towards determining the planar S-matrix of maximally supersymmetric Yang-Mills theory, thanks to the rich interplay between its perturbative analytic properties in general kinematics, and its integrable structure in special kinematics. The former are related to cluster algebras, and allow for the computation of amplitudes with six/seven gluons up to six/four loops, whereas the latter yields all amplitudes in the multi-Regge limit at finite coupling.
Posted by: QMW
Wed
18 Apr 2018
Feynman Integrals: symmetries and seagulls
Ruth Shir
(Hebrew University of Jerusalem)
Abstract:
Feynman diagrams will be looked at from a new point of view. 'Symmetries of Feynman Integrals' is an analytical method for calculating Feynman diagrams. It is based on exposing an underlying group structure of a given diagram which defines a set of partial differential equations in the parameter space of the diagram. Group orbits in the diagram’s parameter space are used to reduce the Feynman integral into a line integral. The vacuum seagull, a three-loop diagram, and the propagator seagull, a propagator-type diagram with two loops, will be used to demonstrate the method, and to obtain new results.
Feynman diagrams will be looked at from a new point of view. 'Symmetries of Feynman Integrals' is an analytical method for calculating Feynman diagrams. It is based on exposing an underlying group structure of a given diagram which defines a set of partial differential equations in the parameter space of the diagram. Group orbits in the diagram’s parameter space are used to reduce the Feynman integral into a line integral. The vacuum seagull, a three-loop diagram, and the propagator seagull, a propagator-type diagram with two loops, will be used to demonstrate the method, and to obtain new results.
Posted by: QMW
Tue
3 Apr 2018
tba
Luca Tagliacozzo
(Strathclyde)
March 2018
Wed
28 Mar 2018
The 11th meeting of the South East Mathematical Physics
Conference Surrey
(Surrey)
Abstract:
The 11th meeting of the South East Mathematical Physics Seminars (SEMPS) will take place at the University of Surrey on Wednesday 28 March 2018.
More information:
http://personal.maths.surrey.ac.uk/st/A.Prinsloo/semps11/semps11.htm
The 11th meeting of the South East Mathematical Physics Seminars (SEMPS) will take place at the University of Surrey on Wednesday 28 March 2018.
More information:
http://personal.maths.surrey.ac.uk/st/A.Prinsloo/semps11/semps11.htm
Posted by: KCL
Wed
28 Mar 2018
Topological AdS/CFT
📍 London
James Sparks
(Oxford)
Abstract:
TBA
TBA
Posted by: KCL
Wed
28 Mar 2018
A new twist on toroidal string compactifications
Mariana Grana
(IPhT Saclay)
Abstract:
TBA
TBA
Posted by: QMW
Tue
27 Mar 2018
Complete factorization in minimal N=4 Chern-Simons-matter theory
📍 London
Shuichi Yokoyama
(Kyoto University)
Abstract:
I and my collaborator, T.Nosaka, revisited minimal N = 4 Chern-Simons theories from its exact S3 partition function, which reduces to finite-dimensional matrix models by supersymmetric localization. We found some new aspects of this interesting model and main results are listed below.
[1] The integration in a matrix model of S3 partition function may be performed completely by using the technique called the Fermi-gas analysis.
[2] The resulting partition function completely factorized into that of pure CS theory for two gauge groups and an analogous contribution for the bifundamental hypermultiplet. We call this complete factorization.
[3] We presented the all order ’t Hooft expansion of the free energy and discussed the connection to the higher-spin theory in the dual gravity side.
[4] The level/rank (or Seiberg-like) duality, which is expected from the Hanany-Witten transition in the type IIB brane realization, was confirmed from the factorized partition function up to an overall factor, which may be a signal of existence of some decoupled sector.
If time permits, I may touch our ongoing analysis of such decoupled sector more precisely by using a superconformal index.
I and my collaborator, T.Nosaka, revisited minimal N = 4 Chern-Simons theories from its exact S3 partition function, which reduces to finite-dimensional matrix models by supersymmetric localization. We found some new aspects of this interesting model and main results are listed below.
[1] The integration in a matrix model of S3 partition function may be performed completely by using the technique called the Fermi-gas analysis.
[2] The resulting partition function completely factorized into that of pure CS theory for two gauge groups and an analogous contribution for the bifundamental hypermultiplet. We call this complete factorization.
[3] We presented the all order ’t Hooft expansion of the free energy and discussed the connection to the higher-spin theory in the dual gravity side.
[4] The level/rank (or Seiberg-like) duality, which is expected from the Hanany-Witten transition in the type IIB brane realization, was confirmed from the factorized partition function up to an overall factor, which may be a signal of existence of some decoupled sector.
If time permits, I may touch our ongoing analysis of such decoupled sector more precisely by using a superconformal index.
Posted by: KCL
Tue
27 Mar 2018
CANCELLED
Ziad Musslimani
(FSU)
Thu
22 Mar 2018
On the scaling limit of the integer quantum Hall plateau transition
Martin Zirnbauer
(University of Cologne)
Abstract:
The scaling behavior near the transition between plateaus of the integer quantum Hall effect has traditionally been interpreted on the basis of a two-parameter renormalization group flow conjectured from the non-linear sigma model of Pruisken. Yet, this scaling picture never led to any analytical understanding of the critical point. Here we propose a novel description of the critical point as Pruisken's nonlinear sigma model coupled to a maximally gauged Wess-Zumino-Witten model of level 4. This proposal explains the existing numerical data for the multifractal scaling exponents of critical wavefunctions.
The scaling behavior near the transition between plateaus of the integer quantum Hall effect has traditionally been interpreted on the basis of a two-parameter renormalization group flow conjectured from the non-linear sigma model of Pruisken. Yet, this scaling picture never led to any analytical understanding of the critical point. Here we propose a novel description of the critical point as Pruisken's nonlinear sigma model coupled to a maximally gauged Wess-Zumino-Witten model of level 4. This proposal explains the existing numerical data for the multifractal scaling exponents of critical wavefunctions.
Posted by: QMW
Wed
21 Mar 2018
Higher spin geometries
📍 London
Per Sundell
(Andres Bello University)
Abstract:
We review the global formulation of higher spin gravity using topological field theory methods and non-commutative geometry and related recent progress in constructing micro states for black holes, domain walls and cosmologies.
We review the global formulation of higher spin gravity using topological field theory methods and non-commutative geometry and related recent progress in constructing micro states for black holes, domain walls and cosmologies.
Posted by: KCL
Wed
21 Mar 2018
Polygon Seminar: Tales from the Edge
📍 London
Christopher Herzog
(KCL)
Abstract:
I discuss some aspects of boundary conformal field theories (bCFTs) with an emphasis on space-time dimensions greater than two. I will demonstrate that free bCFTs have a universal way of satisfying crossing symmetry constraints. I will introduce a simple class of interacting bCFTs where the interaction is restricted to the boundary. Finally, I will discuss relationships between boundary trace anomalies and boundary limits of stress-tensor correlation functions.
(Tea and biscuits + wine at the end!)
I discuss some aspects of boundary conformal field theories (bCFTs) with an emphasis on space-time dimensions greater than two. I will demonstrate that free bCFTs have a universal way of satisfying crossing symmetry constraints. I will introduce a simple class of interacting bCFTs where the interaction is restricted to the boundary. Finally, I will discuss relationships between boundary trace anomalies and boundary limits of stress-tensor correlation functions.
(Tea and biscuits + wine at the end!)
Posted by: KCL
Tue
20 Mar 2018
tba
Nuno Freitas
(Warwick and KCL)
Thu
15 Mar 2018
Conformal bootstrap at large charge
Daniel Jafferis
(Harvard U.)
Wed
14 Mar 2018
TBA
📍 London
Daniel Jafferis
(Harvard University)
Abstract:
TBA
TBA
Posted by: KCL
Tue
13 Mar 2018
tba
Attila Csikasz-Nagy
(KCL)
Wed
7 Mar 2018
Triangle Seminar–Aristotelian QFT, Supersymmetry and Naturalness
Petr Horava
(UC Berkeley)
February 2018
Wed
28 Feb 2018
Aspects of defects and integrability
📍 London
Edward Corrigan
(York University)
Abstract:
The talk will be a review of some of the properties of defects that can be supported by at least some integrable field theories describing massive scalar particles, including the apparently central role played by energy and momentum stored by the defect. The sine-Gordon model is the simplest of these, and for this talk the main example, but there are many others. There are a number of open problems in both the classical and quantum field theory that will be described.
The talk will be a review of some of the properties of defects that can be supported by at least some integrable field theories describing massive scalar particles, including the apparently central role played by energy and momentum stored by the defect. The sine-Gordon model is the simplest of these, and for this talk the main example, but there are many others. There are a number of open problems in both the classical and quantum field theory that will be described.
Posted by: KCL
Tue
27 Feb 2018
Topological strings and 6d SCFTs
Amir-Kian Kashani-Poor
(ENS)
Abstract:
The topological string is a simplified version of physical string theory. It is of interest because it computes the BPS spectrum of relevant string theory compactifications, but also because it shares structural properties of physical string theory, Dualities and symmetries which often must be argued for arduously in the physical string can often be verified by computation in the topological setting. The central observable of the theory is the topological string partition function Z_top. This quantity has an eerie habit of making surprise appearances in many areas of mathematical physics. Numerous techniques exist for its computation in various expansions in parameters of the theory, yet to date, no satisfactory closed form for this quantity is known. In this talk, after reviewing notions of topological string theory with an emphasis on the interplay between worldsheet and target space physics (one of the structural similarities between the physical and the topological string alluded to above), I will report on progress in computing Z_top in settings where it is related to enigmatic 6d theories.
The topological string is a simplified version of physical string theory. It is of interest because it computes the BPS spectrum of relevant string theory compactifications, but also because it shares structural properties of physical string theory, Dualities and symmetries which often must be argued for arduously in the physical string can often be verified by computation in the topological setting. The central observable of the theory is the topological string partition function Z_top. This quantity has an eerie habit of making surprise appearances in many areas of mathematical physics. Numerous techniques exist for its computation in various expansions in parameters of the theory, yet to date, no satisfactory closed form for this quantity is known. In this talk, after reviewing notions of topological string theory with an emphasis on the interplay between worldsheet and target space physics (one of the structural similarities between the physical and the topological string alluded to above), I will report on progress in computing Z_top in settings where it is related to enigmatic 6d theories.
Posted by: CityU2
Fri
23 Feb 2018
All-point correlation functions in SYK
📍 London
Vladimir Rosenhaus
(University of California)
Abstract:
The SYK model, and more generally, tensor models, are a new class of large N quantum field theories. We discuss the computation of all-point correlation functions in the SYK model, at leading order in 1/N. The result has remarkable simplicity and structure. The result is general, holding for any theory in which one forms higher-point correlators by gluing together four-point functions; for instance, large N vector models and tensor models. It implies specific singularity structure of analytically extended OPE coefficients. In particular, the analytically extended OPE coefficients of the single-trace operators encode the OPE coefficients of the double-trace operators.
The SYK model, and more generally, tensor models, are a new class of large N quantum field theories. We discuss the computation of all-point correlation functions in the SYK model, at leading order in 1/N. The result has remarkable simplicity and structure. The result is general, holding for any theory in which one forms higher-point correlators by gluing together four-point functions; for instance, large N vector models and tensor models. It implies specific singularity structure of analytically extended OPE coefficients. In particular, the analytically extended OPE coefficients of the single-trace operators encode the OPE coefficients of the double-trace operators.
Posted by: KCL
Thu
22 Feb 2018
Knot Invariants and M theory
Radu Tatar
(Liverpool U.)
Abstract:
Brane construction with certain boundary conditions are used to study knot invariants and Khovanov homology. We argue that seven-dimensional manifolds in M-theory give rise to the topological theories may appear from certain twisting of the G-flux action. We discuss explicit constructions of the seven-dimensional manifolds in M-theory, and show that both the localization equations and surface operators appear naturally from the Hamiltonian formalism of the theories. Knots and link invariants are then constructed using M2-brane states in both the models.
Brane construction with certain boundary conditions are used to study knot invariants and Khovanov homology. We argue that seven-dimensional manifolds in M-theory give rise to the topological theories may appear from certain twisting of the G-flux action. We discuss explicit constructions of the seven-dimensional manifolds in M-theory, and show that both the localization equations and surface operators appear naturally from the Hamiltonian formalism of the theories. Knots and link invariants are then constructed using M2-brane states in both the models.
Posted by: QMW
Wed
21 Feb 2018
Conformal Fishnet Theory
📍 London
Vladimir Kazakov
(ENS Paris)
Abstract:
I will discuss the properties of a family of four-dimensional CFTs, recently proposed by O.Gurdogan and myself, emerging as a double scaling limit of weakly coupled and strongly gamma-twisted N=4 SYM theory. These non-unitary CFTs inherit the integrability of N=4 SYM in the planar limit and present a unique opportunity of a non-perturbative study of four-dimensional conformal physics. Important physical quantities are dominated by a limited subset of Feynman graphs (such as "fishnet" graphs for the simplest, bi-scalar model). I present the results of exact calculation of some of these quantities, such as anomalous dimensions of local operators, some 3- and 4point correlation functions and scattering amplitudes, by means of spin chain techniques or the quantum spectral curve (QSC) approach originally proposed for N=4 SYM.
I will discuss the properties of a family of four-dimensional CFTs, recently proposed by O.Gurdogan and myself, emerging as a double scaling limit of weakly coupled and strongly gamma-twisted N=4 SYM theory. These non-unitary CFTs inherit the integrability of N=4 SYM in the planar limit and present a unique opportunity of a non-perturbative study of four-dimensional conformal physics. Important physical quantities are dominated by a limited subset of Feynman graphs (such as "fishnet" graphs for the simplest, bi-scalar model). I present the results of exact calculation of some of these quantities, such as anomalous dimensions of local operators, some 3- and 4point correlation functions and scattering amplitudes, by means of spin chain techniques or the quantum spectral curve (QSC) approach originally proposed for N=4 SYM.
Posted by: KCL
Wed
21 Feb 2018
Polygon Seminar
Kostas Skenderis and Andrei Starinets
(Southampton, Oxford)
Abstract:
Kostas Skenderis:
Title: "Towards a general AdS/Ricci-flat correspondence"
Abstract:
The AdS/Ricci-flat (AdS/RF) correspondence is a map between families of asymptotically locally AdS solutions on a torus and families of asymptotically flat spacetimes on a sphere. In this talk I will discuss how to relax these restrictions for linearized perturbations around solutions connected via the original AdS/RF correspondence.
This correspondence should allow us to develop a detailed holographic dictionary for asymptotically flat spacetimes.
Andrei Starinets: TBA
Kostas Skenderis:
Title: "Towards a general AdS/Ricci-flat correspondence"
Abstract:
The AdS/Ricci-flat (AdS/RF) correspondence is a map between families of asymptotically locally AdS solutions on a torus and families of asymptotically flat spacetimes on a sphere. In this talk I will discuss how to relax these restrictions for linearized perturbations around solutions connected via the original AdS/RF correspondence.
This correspondence should allow us to develop a detailed holographic dictionary for asymptotically flat spacetimes.
Andrei Starinets: TBA
Posted by: IC
Tue
20 Feb 2018
A review of Double and Exceptional Field Theory
David Berman
(QMUL)
Abstract:
Recently a new formulation for supergravity has emerged inspired by the presence of duality symmetries in reduced theories. These new theories generalise ideas of Riemannian geometry and lead to new ways of looking at string and M-theory.
Recently a new formulation for supergravity has emerged inspired by the presence of duality symmetries in reduced theories. These new theories generalise ideas of Riemannian geometry and lead to new ways of looking at string and M-theory.
Posted by: CityU2
Mon
19 Feb 2018
All-point correlation functions in SYK
Vladimir Rosenhaus
(KITP)
Abstract:
We discuss the computation of all-point correlation functions in the SYK model, at leading order in 1/N. The result has remarkable simplicity and structure. The result is general, holding for any theory in which one forms higher-point correlators by gluing together four-point functions; for instance, large N vector models and tensor models. It implies specific singularity structure of analytically extended OPE coefficients. In particular, the analytically extended OPE coefficients of the single-trace operators encode the OPE coefficients of the double-trace operators
We discuss the computation of all-point correlation functions in the SYK model, at leading order in 1/N. The result has remarkable simplicity and structure. The result is general, holding for any theory in which one forms higher-point correlators by gluing together four-point functions; for instance, large N vector models and tensor models. It implies specific singularity structure of analytically extended OPE coefficients. In particular, the analytically extended OPE coefficients of the single-trace operators encode the OPE coefficients of the double-trace operators
Posted by: IC
Thu
15 Feb 2018
Exceptional geometry for affine and other groups
Axel Kleinschmidt
(MPI Potsdam)
Abstract:
Exceptional geometry is an attempt to combine the geometric diffeomorphisms and matter gauge transformations in gravity-matter theories into a single geometric structure. I will review recent results associated with a 2+9 split of maximal supergravity where the affine symmetry group E9 plays a central role. The results also provide a general formula that is applicable to many other cases.
Exceptional geometry is an attempt to combine the geometric diffeomorphisms and matter gauge transformations in gravity-matter theories into a single geometric structure. I will review recent results associated with a 2+9 split of maximal supergravity where the affine symmetry group E9 plays a central role. The results also provide a general formula that is applicable to many other cases.
Posted by: QMW
Wed
14 Feb 2018
Highly Supersymmetric AdS Solutions
📍 London
Jan Gutowski
(Surrey University)
Abstract:
Anti-de-Sitter solutions play an important role in the
gauge-theory/gravity correspondence, and understanding
their properties has provided important insights into
the dual field theories. We consider ADS solutions
which are highly supersymmetric, in the sense that they
preserve more than 16 supersymmetries, and show how
how modified versions of the homogeneity theorems of
Figureoa-O'Farrill, combined with aspects of the global
properties of the geometries, can be used to classify
these solutions.
Anti-de-Sitter solutions play an important role in the
gauge-theory/gravity correspondence, and understanding
their properties has provided important insights into
the dual field theories. We consider ADS solutions
which are highly supersymmetric, in the sense that they
preserve more than 16 supersymmetries, and show how
how modified versions of the homogeneity theorems of
Figureoa-O'Farrill, combined with aspects of the global
properties of the geometries, can be used to classify
these solutions.
Posted by: KCL
Wed
14 Feb 2018
Differential equations for loop integrals without squared propagators
Kasper Larsen
(U. Southampton)
Abstract:
A powerful approach to compute multi-loop Feynman integrals is to reduce the integrals to a basis of integrals and set up a first-order linear system of partial differential equations for the basis integrals. In this talk I will discuss the differential equations that arise when the loop integrals are parametrized in Baikov representation. In particular, I give a proof that dimension shifts (which are undesirable) can always be avoided. I will moreover show that in a large class of two- and three-loop diagrams it is possible to avoid integrals with squared propagators in the intermediate stages of setting up the differential equations. This is interesting because it implies that the differential equations can be set up using a smaller set of reductions.
A powerful approach to compute multi-loop Feynman integrals is to reduce the integrals to a basis of integrals and set up a first-order linear system of partial differential equations for the basis integrals. In this talk I will discuss the differential equations that arise when the loop integrals are parametrized in Baikov representation. In particular, I give a proof that dimension shifts (which are undesirable) can always be avoided. I will moreover show that in a large class of two- and three-loop diagrams it is possible to avoid integrals with squared propagators in the intermediate stages of setting up the differential equations. This is interesting because it implies that the differential equations can be set up using a smaller set of reductions.
Posted by: QMW
Tue
13 Feb 2018
Emergent hydrodynamics in integrable systems out of equilibrium
Benjamin Doyon
(King's)
Abstract:
The hydrodynamic approximation is an extremely powerful tool to describe the behavior of many-body systems such as gases. At the Euler scale (that is, when variations of densities and currents occur only on large space-time scales), the approximation is based on the idea of local thermodynamic equilibrium: locally, within fluid cells, the system is in a Galilean or relativistic boost of a Gibbs equilibrium state. This is expected to arise in conventional gases thanks to ergodicity and Gibbs thermalization, which in the quantum case is embodied by the eigenstate thermalization hypothesis. However, integrable systems are well known not to thermalize in the standard fashion. The presence of infinitely-many conservation laws preclude Gibbs thermalization, and instead generalized Gibbs ensembles emerge. In this talk I will introduce the associated theory of generalized hydrodynamics (GHD), which applies the hydrodynamic ideas to systems with infinitely-many conservation laws. It describes the dynamics from inhomogeneous states and in inhomogeneous force fields, and is valid both for quantum systems such as experimentally realized one-dimensional interacting Bose gases and quantum Heisenberg chains, and classical ones such as soliton gases and classical field theory. I will give an overview of what GHD is, how its main equations are derived and its relation to quantum and classical integrable systems. If time permits I will touch on the geometry that lies at its core, how it reproduces the effects seen in the famous quantum Newton cradle experiment, and how it leads to exact results in transport problems such as Drude weights and non-equilibrium currents.
This is based on various collaborations with Alvise Bastianello, Olalla Castro Alvaredo, Jean-Sébastien Caux, Jérôme Dubail, Robert Konik, Herbert Spohn, Gerard Watts and my student Takato Yoshimura, and strongly inspired by previous collaborations with Denis Bernard, M. Joe Bhaseen, Andrew Lucas and Koenraad Schalm.
The hydrodynamic approximation is an extremely powerful tool to describe the behavior of many-body systems such as gases. At the Euler scale (that is, when variations of densities and currents occur only on large space-time scales), the approximation is based on the idea of local thermodynamic equilibrium: locally, within fluid cells, the system is in a Galilean or relativistic boost of a Gibbs equilibrium state. This is expected to arise in conventional gases thanks to ergodicity and Gibbs thermalization, which in the quantum case is embodied by the eigenstate thermalization hypothesis. However, integrable systems are well known not to thermalize in the standard fashion. The presence of infinitely-many conservation laws preclude Gibbs thermalization, and instead generalized Gibbs ensembles emerge. In this talk I will introduce the associated theory of generalized hydrodynamics (GHD), which applies the hydrodynamic ideas to systems with infinitely-many conservation laws. It describes the dynamics from inhomogeneous states and in inhomogeneous force fields, and is valid both for quantum systems such as experimentally realized one-dimensional interacting Bose gases and quantum Heisenberg chains, and classical ones such as soliton gases and classical field theory. I will give an overview of what GHD is, how its main equations are derived and its relation to quantum and classical integrable systems. If time permits I will touch on the geometry that lies at its core, how it reproduces the effects seen in the famous quantum Newton cradle experiment, and how it leads to exact results in transport problems such as Drude weights and non-equilibrium currents.
This is based on various collaborations with Alvise Bastianello, Olalla Castro Alvaredo, Jean-Sébastien Caux, Jérôme Dubail, Robert Konik, Herbert Spohn, Gerard Watts and my student Takato Yoshimura, and strongly inspired by previous collaborations with Denis Bernard, M. Joe Bhaseen, Andrew Lucas and Koenraad Schalm.
Posted by: CityU2
Thu
8 Feb 2018
S-matrix bootstrap for large N confining gauge theories
📍 London
Amit Sever
(Tel-Aviv University)
Abstract:
In the talk I'll consider theories of weakly interacting higher spin particles in flat spacetime. We will focus on the four-point scattering amplitude at high energies and imaginary scattering angles. Both, the leading asymptotic of the amplitude and the first sub-leading correction in this regime turn out to be universal. The leading asymptotic is equal to the corresponding limit of the Veneziano amplitude. We will compute the first sub-leading correction using a model of relativistic strings with massive endpoints and argue that it is unique using holography, the effective theory of long strings and bootstrap techniques.
In the talk I'll consider theories of weakly interacting higher spin particles in flat spacetime. We will focus on the four-point scattering amplitude at high energies and imaginary scattering angles. Both, the leading asymptotic of the amplitude and the first sub-leading correction in this regime turn out to be universal. The leading asymptotic is equal to the corresponding limit of the Veneziano amplitude. We will compute the first sub-leading correction using a model of relativistic strings with massive endpoints and argue that it is unique using holography, the effective theory of long strings and bootstrap techniques.
Posted by: KCL
Thu
8 Feb 2018
Holographic Effective Field Theories for Charge Density Wave States
Daniele Musso
(IGFAE)
Abstract:
The spatially modulated self-organization of strongly-correlated electrons
is central in describing the phenomenology of many condensed matter systems,
such as the cuprates and the manganites. Holography can describe spontaneous
formation of various kinds of density waves in a strongly-coupled media and
provides toy-model effective field theories able to capture important
phenomenological features, such as the low-temperature scaling of the conductivity.
Appropriate UV completions of the holographic EFT can also describe the spontaneous
generation of the spatial features themselves.
The spatially modulated self-organization of strongly-correlated electrons
is central in describing the phenomenology of many condensed matter systems,
such as the cuprates and the manganites. Holography can describe spontaneous
formation of various kinds of density waves in a strongly-coupled media and
provides toy-model effective field theories able to capture important
phenomenological features, such as the low-temperature scaling of the conductivity.
Appropriate UV completions of the holographic EFT can also describe the spontaneous
generation of the spatial features themselves.
Posted by: IC
Wed
7 Feb 2018
Triangle Seminar: Exploring EPR=ER with LLM
Joan Simon
(Edinburgh)
Abstract:
The extremal limit of single R-charged AdS5 black holes in type IIB is known to be described by a system of N free fermions in a one dimensional harmonic oscillator potential. Since the quantum mechanical problem is solvable and its phase space formulation appears in the gravity dual (LLM geometries), it allows us to explore the relation between entanglement, quantum correlation design and connectivity in space in this set-up, both in a single and a two boundary situation.
The extremal limit of single R-charged AdS5 black holes in type IIB is known to be described by a system of N free fermions in a one dimensional harmonic oscillator potential. Since the quantum mechanical problem is solvable and its phase space formulation appears in the gravity dual (LLM geometries), it allows us to explore the relation between entanglement, quantum correlation design and connectivity in space in this set-up, both in a single and a two boundary situation.
Posted by: CityU2
Wed
7 Feb 2018
Scattering Amplitudes – Wilson Loops Duality for the first non-planar correction
Amit Sever
(CERN)
Abstract:
We study non-planar corrections to gluon scattering amplitudes in N = 4 SYM theory. In this talk, we focus on the first correction. It is computed by the double trace amplitude and is suppressed by one power of 1/Nc with respect to the leading single trace contribution. We extend the duality between planar scattering amplitudes and null polygonal Wilson loops to the double trace amplitude. The new duality allows us to extend the notion of loop integrand beyond the planar limit and to determine it using recursion relation. It also allows us to apply the integrability pentagon approach to the first non-planar order. We shortly discuss higher orders in the 't Hooft 1/Nc expansion.
We study non-planar corrections to gluon scattering amplitudes in N = 4 SYM theory. In this talk, we focus on the first correction. It is computed by the double trace amplitude and is suppressed by one power of 1/Nc with respect to the leading single trace contribution. We extend the duality between planar scattering amplitudes and null polygonal Wilson loops to the double trace amplitude. The new duality allows us to extend the notion of loop integrand beyond the planar limit and to determine it using recursion relation. It also allows us to apply the integrability pentagon approach to the first non-planar order. We shortly discuss higher orders in the 't Hooft 1/Nc expansion.
Posted by: CityU2
Tue
6 Feb 2018
AdS3 holographic correlators with heavy states
Rodolfo Russo
(QMUL)
Abstract:
The AdS/CFT duality maps supersymmetric heavy operators with
conformal dimension of the order of the central charge to asymptotically AdS supergravity solutions. I'll show how by studying the quadratic fluctuations around such backgrounds it is possible to derive the 4-point correlators of two light and two heavy states in the supergravity approximation. I'll present some explicit examples in the AdS3 setup relevant for the duality with the D1-D5 CFT and discuss what we can learn in general about correlators among heavy pure states.
The AdS/CFT duality maps supersymmetric heavy operators with
conformal dimension of the order of the central charge to asymptotically AdS supergravity solutions. I'll show how by studying the quadratic fluctuations around such backgrounds it is possible to derive the 4-point correlators of two light and two heavy states in the supergravity approximation. I'll present some explicit examples in the AdS3 setup relevant for the duality with the D1-D5 CFT and discuss what we can learn in general about correlators among heavy pure states.
Posted by: CityU2
Thu
1 Feb 2018
The Search for the Exotic: Subfactors and Conformal Field Theory
David Evans
Abstract:
I will discuss the programme to understand conformal field theory via subfactors and twisted equivariant K-theory. This has also resulted in a better understanding of the double of the Haagerup subfactor, which was previously thought to be exotic and un-related to known models.
I will discuss the programme to understand conformal field theory via subfactors and twisted equivariant K-theory. This has also resulted in a better understanding of the double of the Haagerup subfactor, which was previously thought to be exotic and un-related to known models.
Posted by: QMW
January 2018
Wed
31 Jan 2018
Quantum Spectral Curve and correlators in N=4 SYM
📍 London
Nikolay Gromov
(King's College London)
Abstract:
We discuss the applicability of the Quantum Spectral Curve approach (the most advanced and precise method initially developed for the spectrum of anomalous dimensions of planar N=4 SYM) to the problem of computing structure constants.
We give a pedagogical introduction to the QSC formalism for the anomalous dimensions and then present our new results about a more general class observables.
We discuss the applicability of the Quantum Spectral Curve approach (the most advanced and precise method initially developed for the spectrum of anomalous dimensions of planar N=4 SYM) to the problem of computing structure constants.
We give a pedagogical introduction to the QSC formalism for the anomalous dimensions and then present our new results about a more general class observables.
Posted by: KCL
Tue
30 Jan 2018
tba
Istvan Szecsenyi
(City)
Thu
25 Jan 2018
The Yang-Mills origin of all homogeneous N=2 supergravities
Alexandros Anastasiou
(NORDITA)
Abstract:
Squaring involves the tensoring between the state content of two super Yang-Mills (sYM) theories to obtain the state content of a supergravity theory. Understanding the YM origin of gravitational symmetries is a powerful tool towards classifying gravity theories which admit such a factorisation. In the first part of the talk I will show how the global symmetries of a pair of sYM theories combine to form those of the corresponding supergravity. In the second part I will discuss how these tools can be further extended to sYM coupled to matter such that squaring can give all ungauged N=2 supergravities with homogeneous scalar manifold.
Squaring involves the tensoring between the state content of two super Yang-Mills (sYM) theories to obtain the state content of a supergravity theory. Understanding the YM origin of gravitational symmetries is a powerful tool towards classifying gravity theories which admit such a factorisation. In the first part of the talk I will show how the global symmetries of a pair of sYM theories combine to form those of the corresponding supergravity. In the second part I will discuss how these tools can be further extended to sYM coupled to matter such that squaring can give all ungauged N=2 supergravities with homogeneous scalar manifold.
Posted by: QMW
Thu
18 Jan 2018
Numerical Simulations of Asymptotically AdS Spacetimes
Hans Bantilan
(QMUL)
Abstract:
The main purpose of this talk is to describe, by way of concrete examples, how the field of numerical relativity now contributes to our understanding of open questions in gravitational collapse, heavy-ion physics, and turbulence. I will begin by motivating these studies in terms of the physical systems they are intended to clarify,then provide specific examples of how to describe these systems with numerical simulations of asymptotically AdS spacetimes in the fully non-linear regime of general relativity.
The main purpose of this talk is to describe, by way of concrete examples, how the field of numerical relativity now contributes to our understanding of open questions in gravitational collapse, heavy-ion physics, and turbulence. I will begin by motivating these studies in terms of the physical systems they are intended to clarify,then provide specific examples of how to describe these systems with numerical simulations of asymptotically AdS spacetimes in the fully non-linear regime of general relativity.
Posted by: QMW
Thu
11 Jan 2018
Spacetime as a resource
Joan Simon
(U. of Edinburgh)
Abstract:
The relation between black holes and thermodynamics leading to the holographic principle is well known. Formulating thermodynamics as the theory of transformations performing some work or task allows us to reinterpret recent developments in AdS/CFT, such as the holographic description of entanglement entropy, as a measure of the connectivity of space (resource). Whether spacetime in the interior of a black hole also allows an understanding as a resource is an interesting open question.
The relation between black holes and thermodynamics leading to the holographic principle is well known. Formulating thermodynamics as the theory of transformations performing some work or task allows us to reinterpret recent developments in AdS/CFT, such as the holographic description of entanglement entropy, as a measure of the connectivity of space (resource). Whether spacetime in the interior of a black hole also allows an understanding as a resource is an interesting open question.
Posted by: QMW