Triangle Seminars
July 2017
Wed
5 Jul 2017
Holography of BCFT
Chong-Sun Chu
(NCTS, Hsinchu and Taiwan, Natl. Tsing Hua U.)
Abstract:
In this talk, I will discuss about the holography of boundary Conformal Field theory. I will show how boundary Weyl Anomaly can be obtained from holography. New universal relations between the shape dependence of Casimir effects and boundary Weyl anomaly will also be pointed out and discussed from the point of view of holography.
In this talk, I will discuss about the holography of boundary Conformal Field theory. I will show how boundary Weyl Anomaly can be obtained from holography. New universal relations between the shape dependence of Casimir effects and boundary Weyl anomaly will also be pointed out and discussed from the point of view of holography.
Posted by: QMW
Mon
3 Jul 2017
String Geometry, Supersymmetric Theories and Dualities
Surrey Conference
(Surrey University)
Abstract:
Organisers: Andrea Fontanella, Joakim Strömvall (University of Surrey)<br>
<br>
The conference String Geometry, Supersymmetric Theories and Dualities takes place on 3-4 July 2017 at the University of Surrey.
<br><br>
The purpose is to gather a broad audience of researchers and to provide a window into current research. During the first day there will be pedagogical lectures that prepare the ground for the second day, which consists of technical talks.
<br><br>
Prof. Nick Dorey (University of Cambridge):
â€Superconformal quantum mechanics and integrabilityâ€
<br><br>
Prof. Dario Martelli (King’s College London):
â€Supergravity tools for holographyâ€
<br><br>
Prof. Xenia de la Ossa (University of Oxford):
â€Moduli spaces of heterotic compactificationsâ€
<br><br>
On the second day, technical talks will be given by the lecturers and two early career researchers as part of the 9th SEMPS meeting.
<br><br>
see <a href='https://sgstad.blog/'>here</a> for details
Organisers: Andrea Fontanella, Joakim Strömvall (University of Surrey)<br>
<br>
The conference String Geometry, Supersymmetric Theories and Dualities takes place on 3-4 July 2017 at the University of Surrey.
<br><br>
The purpose is to gather a broad audience of researchers and to provide a window into current research. During the first day there will be pedagogical lectures that prepare the ground for the second day, which consists of technical talks.
<br><br>
Prof. Nick Dorey (University of Cambridge):
â€Superconformal quantum mechanics and integrabilityâ€
<br><br>
Prof. Dario Martelli (King’s College London):
â€Supergravity tools for holographyâ€
<br><br>
Prof. Xenia de la Ossa (University of Oxford):
â€Moduli spaces of heterotic compactificationsâ€
<br><br>
On the second day, technical talks will be given by the lecturers and two early career researchers as part of the 9th SEMPS meeting.
<br><br>
see <a href='https://sgstad.blog/'>here</a> for details
Posted by: KCL
June 2017
Thu
29 Jun 2017
Irreversibility of the renormalization group flow in non-unitary quantum field theory
Benjamin Doyon
(KCL)
Abstract:
The talk is based on a very recent work of the speaker on generalising Zamolodchikov's c-theorem to non-unitary theories.
The talk is based on a very recent work of the speaker on generalising Zamolodchikov's c-theorem to non-unitary theories.
Posted by: KCL
Wed
14 Jun 2017
Scattering Amplitudes, Double Copy and Worldsheet Models of QFTs (Lecture 4)
Ricardo Monteiro
(QMUL)
Abstract:
I will give an introduction to current topics in the study of scattering amplitudes of gauge theory and gravity. There will be four two-hour lectures, and the plan is as follows.
Lecture 1 will review basic modern techniques for scattering amplitudes, including recursion relations.
Lecture 2 will present an overview of the relations describing gravity as a double copy of gauge theory, both for scattering amplitudes and for solutions to the equations of motion.
Lecture 3 will introduce the formalism of the scattering equations, leading to the CHY formulas for amplitudes in theories of massless particles.
Lecture 4 will present new developments in computing field-theory amplitudes from string-theory-inspired techniques, via a new type of worldsheet model known as ambitwistor string. This leads to an extension of the scattering equations to loop level.
I will give an introduction to current topics in the study of scattering amplitudes of gauge theory and gravity. There will be four two-hour lectures, and the plan is as follows.
Lecture 1 will review basic modern techniques for scattering amplitudes, including recursion relations.
Lecture 2 will present an overview of the relations describing gravity as a double copy of gauge theory, both for scattering amplitudes and for solutions to the equations of motion.
Lecture 3 will introduce the formalism of the scattering equations, leading to the CHY formulas for amplitudes in theories of massless particles.
Lecture 4 will present new developments in computing field-theory amplitudes from string-theory-inspired techniques, via a new type of worldsheet model known as ambitwistor string. This leads to an extension of the scattering equations to loop level.
Posted by: QMW
Tue
13 Jun 2017
Scattering Amplitudes, Double Copy and Worldsheet Models of QFTs (Lecture 3)
Ricardo Monteiro
(QMUL)
Abstract:
I will give an introduction to current topics in the study of scattering amplitudes of gauge theory and gravity. There will be four two-hour lectures, and the plan is as follows.
Lecture 1 will review basic modern techniques for scattering amplitudes, including recursion relations.
Lecture 2 will present an overview of the relations describing gravity as a double copy of gauge theory, both for scattering amplitudes and for solutions to the equations of motion.
Lecture 3 will introduce the formalism of the scattering equations, leading to the CHY formulas for amplitudes in theories of massless particles.
Lecture 4 will present new developments in computing field-theory amplitudes from string-theory-inspired techniques, via a new type of worldsheet model known as ambitwistor string. This leads to an extension of the scattering equations to loop level.
I will give an introduction to current topics in the study of scattering amplitudes of gauge theory and gravity. There will be four two-hour lectures, and the plan is as follows.
Lecture 1 will review basic modern techniques for scattering amplitudes, including recursion relations.
Lecture 2 will present an overview of the relations describing gravity as a double copy of gauge theory, both for scattering amplitudes and for solutions to the equations of motion.
Lecture 3 will introduce the formalism of the scattering equations, leading to the CHY formulas for amplitudes in theories of massless particles.
Lecture 4 will present new developments in computing field-theory amplitudes from string-theory-inspired techniques, via a new type of worldsheet model known as ambitwistor string. This leads to an extension of the scattering equations to loop level.
Posted by: QMW
Wed
7 Jun 2017
Scattering Amplitudes, Double Copy and Worldsheet Models of QFTs (Lecture 2)
Ricardo Monteiro
(QMUL)
Abstract:
I will give an introduction to current topics in the study of scattering amplitudes of gauge theory and gravity. There will be four two-hour lectures, and the plan is as follows.
Lecture 1 will review basic modern techniques for scattering amplitudes, including recursion relations.
Lecture 2 will present an overview of the relations describing gravity as a double copy of gauge theory, both for scattering amplitudes and for solutions to the equations of motion.
Lecture 3 will introduce the formalism of the scattering equations, leading to the CHY formulas for amplitudes in theories of massless particles.
Lecture 4 will present new developments in computing field-theory amplitudes from string-theory-inspired techniques, via a new type of worldsheet model known as ambitwistor string. This leads to an extension of the scattering equations to loop level.
I will give an introduction to current topics in the study of scattering amplitudes of gauge theory and gravity. There will be four two-hour lectures, and the plan is as follows.
Lecture 1 will review basic modern techniques for scattering amplitudes, including recursion relations.
Lecture 2 will present an overview of the relations describing gravity as a double copy of gauge theory, both for scattering amplitudes and for solutions to the equations of motion.
Lecture 3 will introduce the formalism of the scattering equations, leading to the CHY formulas for amplitudes in theories of massless particles.
Lecture 4 will present new developments in computing field-theory amplitudes from string-theory-inspired techniques, via a new type of worldsheet model known as ambitwistor string. This leads to an extension of the scattering equations to loop level.
Posted by: QMW
Tue
6 Jun 2017
Scattering Amplitudes, Double Copy and Worldsheet Models of QFTs (Lecture 1)
Ricardo Monteiro
(QMUL)
Abstract:
I will give an introduction to current topics in the study of scattering amplitudes of gauge theory and gravity. There will be four two-hour lectures, and the plan is as follows:
Lecture 1 will review basic modern techniques for scattering amplitudes, including recursion relations.
Lecture 2 will present an overview of the relations describing gravity as a double copy of gauge theory, both for scattering amplitudes and for solutions to the equations of motion.
Lecture 3 will introduce the formalism of the scattering equations, leading to the CHY formulas for amplitudes in theories of massless particles.
Lecture 4 will present new developments in computing field-theory amplitudes from string-theory-inspired techniques, via a new type of worldsheet model known as ambitwistor string. This leads to an extension of the scattering equations to loop level.
I will give an introduction to current topics in the study of scattering amplitudes of gauge theory and gravity. There will be four two-hour lectures, and the plan is as follows:
Lecture 1 will review basic modern techniques for scattering amplitudes, including recursion relations.
Lecture 2 will present an overview of the relations describing gravity as a double copy of gauge theory, both for scattering amplitudes and for solutions to the equations of motion.
Lecture 3 will introduce the formalism of the scattering equations, leading to the CHY formulas for amplitudes in theories of massless particles.
Lecture 4 will present new developments in computing field-theory amplitudes from string-theory-inspired techniques, via a new type of worldsheet model known as ambitwistor string. This leads to an extension of the scattering equations to loop level.
Posted by: QMW
May 2017
Fri
26 May 2017
Goldstino superfields in supergravity
Sergei Kuzenko
(U Western Australia)
Abstract:
Models with spontaneously broken local supersymmetry are naturally obtained by coupling the off-shell supergravity-matter systems to Goldstino superfields. Every irreducible Goldstino superfield produces a universal positive contribution to the cosmological constant. This talk will review the structure of N=1 and N=2 Goldstino superfields.
Models with spontaneously broken local supersymmetry are naturally obtained by coupling the off-shell supergravity-matter systems to Goldstino superfields. Every irreducible Goldstino superfield produces a universal positive contribution to the cosmological constant. This talk will review the structure of N=1 and N=2 Goldstino superfields.
Posted by: IC
Wed
24 May 2017
Diffusion and Chaos in Holographic Matter
Mike Blake
(MIT)
Abstract:
In this talk I will discuss recent developments that have suggested new connections between the transport properties of strongly interacting matter and the field of quantum chaos. In particular I will describe how in many holographic theories there are simple relationships between the thermoelectric diffusion constants and the butterfly velocity, which describes the speed at which quantum chaos propagates.
In this talk I will discuss recent developments that have suggested new connections between the transport properties of strongly interacting matter and the field of quantum chaos. In particular I will describe how in many holographic theories there are simple relationships between the thermoelectric diffusion constants and the butterfly velocity, which describes the speed at which quantum chaos propagates.
Posted by: IC
Mon
22 May 2017
An introduction to Gauge Theory in Superspace
Rikard von Unge
(Masaryk University)
Abstract:
TBA
TBA
Posted by: IC
Thu
18 May 2017
Double field theory and doubled geometry
Chris Blair
(Vrije U., Brussels)
Abstract:
I will discuss some aspects of the doubled geometry of double field theory. Double field theory provides a reformulation of supergravity with a manifest O(D,D) symmetry, which can be related to the T-duality invariance of string theory on a torus. I will review how one achieves this, by doubling the number of coordinates and introducing a generalised diffeomorphism symmetry. Then, I will discuss how one can characterise the properties of string theory backgrounds viewed as solutions of DFT, and in particular show how to derive the first law of black hole thermodynamics in this framework. Based mainly on 1507.07541 and 1608.04734 (with Alex Arvanitakis).
I will discuss some aspects of the doubled geometry of double field theory. Double field theory provides a reformulation of supergravity with a manifest O(D,D) symmetry, which can be related to the T-duality invariance of string theory on a torus. I will review how one achieves this, by doubling the number of coordinates and introducing a generalised diffeomorphism symmetry. Then, I will discuss how one can characterise the properties of string theory backgrounds viewed as solutions of DFT, and in particular show how to derive the first law of black hole thermodynamics in this framework. Based mainly on 1507.07541 and 1608.04734 (with Alex Arvanitakis).
Posted by: IC
Fri
12 May 2017
Module classification in conformal field theory through symmetric polynomials
📍 London
Simon Wood
(Cardiff)
Abstract:
Given some chiral conformal field theory (also known as a vertex operator algebra in the mathematics literature), a natural but highly non-trivial task is to classify its representation theory. In this talk, I will use some well known examples of conformal field theories, such as the Virasoro minimal models, to show how certain hard questions in representation theory can be neatly rephrased as comparatively easy questions in the theory of symmetric polynomials. After a brief overview of the theory of symmetric polynomials, I will show how they can be used to classify irreducible representations.
Given some chiral conformal field theory (also known as a vertex operator algebra in the mathematics literature), a natural but highly non-trivial task is to classify its representation theory. In this talk, I will use some well known examples of conformal field theories, such as the Virasoro minimal models, to show how certain hard questions in representation theory can be neatly rephrased as comparatively easy questions in the theory of symmetric polynomials. After a brief overview of the theory of symmetric polynomials, I will show how they can be used to classify irreducible representations.
Posted by: KCL
Wed
10 May 2017
M-theory on deformed Sasaki-Einstein manifolds
Stefanos Katmadas
(IPhT, Saclay)
Abstract:
Compactifications of M-theory down to AdS4 are known to arise from Sasaki-Einstein internal spaces. The latter can be viewed as surfaces enclosing Calabi-Yau cone singularities, whose deformations can be described algebraically in a well established way.
In this talk, I will present work in progress on describing deformations of the enclosing surfaces away from the Sasaki-Einstein metric, using the deformations of the Calabi-Yau cone. This provides a realisation of a class of SU(3) structure manifolds satisfying the conditions postulated in the standard treatments of M-theory compactifications on such manifolds.
The result is a proposal for obtaining four dimensional N=2 supergravity models with gauged hypermultiplets from deformations of regular Sasaki-Einstein manifolds.
Compactifications of M-theory down to AdS4 are known to arise from Sasaki-Einstein internal spaces. The latter can be viewed as surfaces enclosing Calabi-Yau cone singularities, whose deformations can be described algebraically in a well established way.
In this talk, I will present work in progress on describing deformations of the enclosing surfaces away from the Sasaki-Einstein metric, using the deformations of the Calabi-Yau cone. This provides a realisation of a class of SU(3) structure manifolds satisfying the conditions postulated in the standard treatments of M-theory compactifications on such manifolds.
The result is a proposal for obtaining four dimensional N=2 supergravity models with gauged hypermultiplets from deformations of regular Sasaki-Einstein manifolds.
Posted by: IC
Fri
5 May 2017
The tale of two dilatons
Paolo Di Vecchia
(NBI/Nordita)
Abstract:
In this talk we will discuss how gauge invariance fixes the soft behavior of massless particles as photons, gluons, gravitons, dilatons and Kalb-Ramond field. We will then check these results in string theory and we will show that the subsubleading behavior for gravitons includes string corrections in the bosonic and heterotic strings, but not in superstring. They are consequence of the fact that the three-graviton amplitude has string corrections with respect to the field theoretical one. It turns out, instead, that the soft behavior of the dilaton has no string corrections and, in particular, involves the generators of dilatations and special conformal transformations. We then study the soft behavior of the Goldstone boson, called in the literature also dilaton, that one gets when one breaks spontaneously the conformal symmetry and we show that its soft behavior is very similar, but not identical, to that of the string dilaton.
In this talk we will discuss how gauge invariance fixes the soft behavior of massless particles as photons, gluons, gravitons, dilatons and Kalb-Ramond field. We will then check these results in string theory and we will show that the subsubleading behavior for gravitons includes string corrections in the bosonic and heterotic strings, but not in superstring. They are consequence of the fact that the three-graviton amplitude has string corrections with respect to the field theoretical one. It turns out, instead, that the soft behavior of the dilaton has no string corrections and, in particular, involves the generators of dilatations and special conformal transformations. We then study the soft behavior of the Goldstone boson, called in the literature also dilaton, that one gets when one breaks spontaneously the conformal symmetry and we show that its soft behavior is very similar, but not identical, to that of the string dilaton.
Posted by: QMW
Wed
3 May 2017
Diffusion and chaos in holographic systems at non-zero density
Richard Davison
(Harvard)
Abstract:
Recent work has uncovered relations between the rate at which chaotic behaviour spreads in strongly interacting quantum systems, and the diffusivities of certain processes in these systems. Focusing mainly on holographic examples, I will explore the extent to which these relations hold in states at non-zero density, where the diffusion of charge and energy are no longer independent processes.
Recent work has uncovered relations between the rate at which chaotic behaviour spreads in strongly interacting quantum systems, and the diffusivities of certain processes in these systems. Focusing mainly on holographic examples, I will explore the extent to which these relations hold in states at non-zero density, where the diffusion of charge and energy are no longer independent processes.
Posted by: IC
Wed
3 May 2017
The 43rd Edwards Lecture: Carlo Rubbia (Nobel Laureate and Former Director General of CERN)
Carlo Rubbia
(CERN)
Abstract:
"The Role of Elementary Particle Accelerators"
http://www.city.ac.uk/events/2017/may/edwards-lecture-the-role-of-elementary-particle-accelerators
(Public lecture and Colloquium)
"The Role of Elementary Particle Accelerators"
http://www.city.ac.uk/events/2017/may/edwards-lecture-the-role-of-elementary-particle-accelerators
(Public lecture and Colloquium)
Posted by: oxford
April 2017
Thu
20 Apr 2017
2D CFT correlators for theories of class S_k
Elli Pomoni
(DESY)
Abstract:
We will introduce a large class of N=1 superconformal theories Sk which is obtained from Gaiotto’s N=2 class S via orbifolding. We will study the Coulomb branch of the theories in the class by constructing and
analyzing their spectral curves. Using our experience from the N=2 AGT correspondence we will search for a 2D/4D relations (AGTk) for the N=1 theories of class Sk. From the curves we will identify the 2D CFT symmetry algebra and its representations, namely the conformal blocks
of the Virasoro/W-algebra, that underlie the 2D theory and reproduce the Seiberg-Witten curves of the N = 1 gauge theories. We find that
the blocks corresponding to the SU(N) Sk gauge theories involve fields in certain non-unitary representations of the WkN algebra. These conformal blocks give a prediction for the instanton partition functions of the 4D N = 1 SCFTs of class Sk.
We will introduce a large class of N=1 superconformal theories Sk which is obtained from Gaiotto’s N=2 class S via orbifolding. We will study the Coulomb branch of the theories in the class by constructing and
analyzing their spectral curves. Using our experience from the N=2 AGT correspondence we will search for a 2D/4D relations (AGTk) for the N=1 theories of class Sk. From the curves we will identify the 2D CFT symmetry algebra and its representations, namely the conformal blocks
of the Virasoro/W-algebra, that underlie the 2D theory and reproduce the Seiberg-Witten curves of the N = 1 gauge theories. We find that
the blocks corresponding to the SU(N) Sk gauge theories involve fields in certain non-unitary representations of the WkN algebra. These conformal blocks give a prediction for the instanton partition functions of the 4D N = 1 SCFTs of class Sk.
Posted by: QMW
Wed
5 Apr 2017
Supersymmetric microstate geometries
Harvey Reall
(Cambridge)
Abstract:
A microstate geometry is a smooth, time-independent, asymptotically flat, horizon-free solution of type IIB supergravity. According to the “fuzzball" conjecture, such solutions describe individual microstates of black holes. Non-supersymmetric microstate geometries typically suffer from linearized instabilities. I will argue that supersymmetric microstate geometries suffer from a nonlinear instability. I will also discuss how such solutions lead to a new type of mathematical structure, so-called “ambipolar†hyperkahler manifolds, and explain how such manifolds can be constructed.
A microstate geometry is a smooth, time-independent, asymptotically flat, horizon-free solution of type IIB supergravity. According to the “fuzzball" conjecture, such solutions describe individual microstates of black holes. Non-supersymmetric microstate geometries typically suffer from linearized instabilities. I will argue that supersymmetric microstate geometries suffer from a nonlinear instability. I will also discuss how such solutions lead to a new type of mathematical structure, so-called “ambipolar†hyperkahler manifolds, and explain how such manifolds can be constructed.
Posted by: IC
March 2017
Thu
30 Mar 2017
What is Dark Matter?
Tommi Tenkanen
(QMUL)
Abstract:
The nature of the unknown non-baryonic energy density component whose abundance is known to exceed the amount of ordinary, visible matter by a factor of five, that of Dark Matter (DM), is one of the greatest open problems in cosmology. In this talk I will briefly review the evidence and searches for DM, present an overview of candidates including the standard WIMP paradigm, and discuss some recently proposed alternatives for WIMPs and how to test them.
The nature of the unknown non-baryonic energy density component whose abundance is known to exceed the amount of ordinary, visible matter by a factor of five, that of Dark Matter (DM), is one of the greatest open problems in cosmology. In this talk I will briefly review the evidence and searches for DM, present an overview of candidates including the standard WIMP paradigm, and discuss some recently proposed alternatives for WIMPs and how to test them.
Posted by: QMW
Wed
29 Mar 2017
Extended Riemannian Geometry and Double Field Theory
📍 London
Christian Samann
(Heriot Watt University)
Abstract:
I present an extended version of Riemannian geometry suitable for the description of current formulations of double field theory (DFT). This framework is based on graded manifolds and it yields extended notions of symmetries, dynamical data and constraints. In special cases, we recover general relativity with and without 1-, 2- and 3-form gauge potentials as well as DFT. We believe that our extended Riemannian geometry helps to clarify the role of various constructions in DFT. For example, it leads to a covariant form of the strong section condition. Furthermore, it should provide a useful
step towards global and coordinate invariant descriptions of T- and U-duality invariant field theories.
I present an extended version of Riemannian geometry suitable for the description of current formulations of double field theory (DFT). This framework is based on graded manifolds and it yields extended notions of symmetries, dynamical data and constraints. In special cases, we recover general relativity with and without 1-, 2- and 3-form gauge potentials as well as DFT. We believe that our extended Riemannian geometry helps to clarify the role of various constructions in DFT. For example, it leads to a covariant form of the strong section condition. Furthermore, it should provide a useful
step towards global and coordinate invariant descriptions of T- and U-duality invariant field theories.
Posted by: KCL
Wed
29 Mar 2017
Yang-Baxter strings, twists, and AdS/CFT
Stijn van Tongeren
(Humboldt U.)
Abstract:
The appearance of integrability in the duality between the AdS5xS5 string and planar maximally supersymmetric Yang-Mills theory gives rise to many insightful results. Various deformations of this AdS/CFT dual pair are known to also be integrable, prompting the question how far the power of integrability extends in this setting. In recent years there has been a lot of progress in answering this question. Rather than trying to demonstrate integrability in known AdS/CFT dual pairs, efforts instead focused on finding manifestly integrability preserving deformations of the AdS5xS5 string. While constructed to preserve integrability, the resulting so-called Yang-Baxter sigma models are, however, not guaranteed to describe strings, or have an AdS/CFT interpretation. The former of these points has since been addressed and turns out to be closely related to (nonabelian) T duality, and we now understand which of these models continue to describe strings. The goal of my talk is to address the latter point, regarding the AdS/CFT interpretation of these models. I will use symmetry considerations to give a unified AdS/CFT picture for these Yang-Baxter strings as duals to various noncommutative deformations of supersymmetric Yang-Mills theory. My general conjecture matches many known dualities, and I will briefly discuss nontrivial tests in various new cases, in the form of brane constructions indicating the desired dualities.
The appearance of integrability in the duality between the AdS5xS5 string and planar maximally supersymmetric Yang-Mills theory gives rise to many insightful results. Various deformations of this AdS/CFT dual pair are known to also be integrable, prompting the question how far the power of integrability extends in this setting. In recent years there has been a lot of progress in answering this question. Rather than trying to demonstrate integrability in known AdS/CFT dual pairs, efforts instead focused on finding manifestly integrability preserving deformations of the AdS5xS5 string. While constructed to preserve integrability, the resulting so-called Yang-Baxter sigma models are, however, not guaranteed to describe strings, or have an AdS/CFT interpretation. The former of these points has since been addressed and turns out to be closely related to (nonabelian) T duality, and we now understand which of these models continue to describe strings. The goal of my talk is to address the latter point, regarding the AdS/CFT interpretation of these models. I will use symmetry considerations to give a unified AdS/CFT picture for these Yang-Baxter strings as duals to various noncommutative deformations of supersymmetric Yang-Mills theory. My general conjecture matches many known dualities, and I will briefly discuss nontrivial tests in various new cases, in the form of brane constructions indicating the desired dualities.
Posted by: IC
Thu
23 Mar 2017
The a-function in 3 dimensions
Ian Jack
(Liverpool)
Abstract:
The a-theorem expressing the monotonicity of renormalisation group flows in four (and other even) dimensions is now well-accepted. There is a function (the a-function) generating the RG beta-functions as a gradient flow via a positive-definite metric. However the standard definition of the a-function in terms of the trace anomaly of the energy-momentum tensor does not work in odd dimensions. In this talk we focus on the gradient-flow property of the a-function and show that a function with similar properties can be constructed order-by-order in three dimensions.
We start by reviewing the a-function in even dimensions from a gradient-flow standpoint. Then we discuss our explicit calculations in three dimensions. Finally we present some progress towards relating our results to the F-function which has been shown to have the expected monotonicity properties at fixed points.
The a-theorem expressing the monotonicity of renormalisation group flows in four (and other even) dimensions is now well-accepted. There is a function (the a-function) generating the RG beta-functions as a gradient flow via a positive-definite metric. However the standard definition of the a-function in terms of the trace anomaly of the energy-momentum tensor does not work in odd dimensions. In this talk we focus on the gradient-flow property of the a-function and show that a function with similar properties can be constructed order-by-order in three dimensions.
We start by reviewing the a-function in even dimensions from a gradient-flow standpoint. Then we discuss our explicit calculations in three dimensions. Finally we present some progress towards relating our results to the F-function which has been shown to have the expected monotonicity properties at fixed points.
Posted by: IC
Wed
22 Mar 2017
Resurgence in Large N Gauge and String Theory
📍 London
Ricardo Schiappa
(Lisbon University)
Abstract:
I will present a light introduction to resurgence, with applications in large N gauge theory and in string theory.
I will present a light introduction to resurgence, with applications in large N gauge theory and in string theory.
Posted by: KCL
Wed
22 Mar 2017
Polygon Seminar: Tree-level scattering amplitudes with the pure spinor formalism
📍 London
Carlos Mafra
(U. Southampton)
Abstract:
I will give a pedagogical review of how the pure spinor formalism was used to obtain all tree-level amplitudes of the superstring, including all their alpha' corrections.
I will give a pedagogical review of how the pure spinor formalism was used to obtain all tree-level amplitudes of the superstring, including all their alpha' corrections.
Posted by: KCL
Thu
16 Mar 2017
Quantum Geometry and Non-Geometric Backgrounds
Richard Szabo
(Heriot-Watt U.)
Abstract:
Recent advances in non-geometric string theory suggest that locally non-geometric flux compactifications can be understood in terms of nonassociative deformations of spacetime geometry. We will review some of these developments and how they shed light on properties of non-geometric strings, and explain some new results concerning how these structures lift to non-geometric M-theory.
Recent advances in non-geometric string theory suggest that locally non-geometric flux compactifications can be understood in terms of nonassociative deformations of spacetime geometry. We will review some of these developments and how they shed light on properties of non-geometric strings, and explain some new results concerning how these structures lift to non-geometric M-theory.
Posted by: IC
Thu
16 Mar 2017
Symmetry and String theory
Menika Sharma
(Harish-Chandra)
Abstract:
String theory in the tensionless limit is expected to have a large gauge symmetry. By recasting string theory on the AdS background as a generalization of Vasiliev's theory of massless higher-spin fields, it has become possible to understand the nature of this symmetry. In this talk, I will first give an overview of three-dimensional Vasiliev theory and its dual CFT. I will then discuss the current understanding of the symmetry algebra of string theory as well as some open problems related to it.
String theory in the tensionless limit is expected to have a large gauge symmetry. By recasting string theory on the AdS background as a generalization of Vasiliev's theory of massless higher-spin fields, it has become possible to understand the nature of this symmetry. In this talk, I will first give an overview of three-dimensional Vasiliev theory and its dual CFT. I will then discuss the current understanding of the symmetry algebra of string theory as well as some open problems related to it.
Posted by: QMW
Wed
15 Mar 2017
Algebraic properties of the monopole formula
Marcus Sperling
(Vienna U.)
Abstract:
In this talk, I will discuss how the two geometric notions "fan" and "monoid" can be very fruitful for the understanding of the monopole formula for 3d N=4 gauge theories.
After a brief reminder of the monopole formula, I will introduce the matter fan and reorganise the monopole formula accordingly. I then discuss the resulting benefits such as:
(1) Explicit expressions for the Hilbert series built from well-studied constituents.
(2) Proof that the order of the pole at t=1 and t → ∞ equals the complex or quaternionic dimension of the Coulomb branch.
(3) Identification of a sufficient set of chiral ring generators.
In this talk, I will discuss how the two geometric notions "fan" and "monoid" can be very fruitful for the understanding of the monopole formula for 3d N=4 gauge theories.
After a brief reminder of the monopole formula, I will introduce the matter fan and reorganise the monopole formula accordingly. I then discuss the resulting benefits such as:
(1) Explicit expressions for the Hilbert series built from well-studied constituents.
(2) Proof that the order of the pole at t=1 and t → ∞ equals the complex or quaternionic dimension of the Coulomb branch.
(3) Identification of a sufficient set of chiral ring generators.
Posted by: IC
Wed
8 Mar 2017
Orbifolds and defects
📍 London
Ingo Runkel
(Hamburg University)
Wed
8 Mar 2017
Localization of supersymmetric field theories on non-compact hyperbolic three-manifolds
Daisuke Yokoyama
(King's College London)
Abstract:
I am going to talk about how to derive an exact partition function of supersymmetric field theories on a supersymmetry-preserving quotient of Euclidean AdS_3 by localization. This is one of first examples about localization on non-compact spaces. I will describe the situation by comparing it to a situation in compact spaces. Then, I will explain how to perform a localization procedure on the manifold, and finally, I will discuss the features of the partition function we derived.
I am going to talk about how to derive an exact partition function of supersymmetric field theories on a supersymmetry-preserving quotient of Euclidean AdS_3 by localization. This is one of first examples about localization on non-compact spaces. I will describe the situation by comparing it to a situation in compact spaces. Then, I will explain how to perform a localization procedure on the manifold, and finally, I will discuss the features of the partition function we derived.
Posted by: IC
Thu
2 Mar 2017
Quantum Geometry and Non-Geometric Backgrounds
Richard Szabo
(Heriot Watt)
Abstract:
Recent advances in non-geometric string theory suggest that locally
non-geometric flux compactifications can be understood in terms of
nonassociative deformations of spacetime geometry. We will review some of
these developments and how they shed light on properties of non-geometric strings, and explain some new results concerning how these structures lift to non-geometric M-theory
Recent advances in non-geometric string theory suggest that locally
non-geometric flux compactifications can be understood in terms of
nonassociative deformations of spacetime geometry. We will review some of
these developments and how they shed light on properties of non-geometric strings, and explain some new results concerning how these structures lift to non-geometric M-theory
Posted by: QMW
Wed
1 Mar 2017
Modular properties of String Scattering Amplitudes
Michael Green
(DAMTP/QMUL)
Abstract:
This talk will focus on some recent results concerning the low energy expansion of superstring scattering amplitudes. Whereas tree-level amplitudes generate a series of multiple zeta values (MZV) the genus-one amplitudes generate a series of elliptic generalisations (“modular graph functionsâ€) that satisfy fascinating polynomial relations analogous to those satisfied by MZV’s.
The latter part of the talk will briefly review how these features fit in with the non-perturbative structure of superstring amplitudes, studied some time ago.
This talk will focus on some recent results concerning the low energy expansion of superstring scattering amplitudes. Whereas tree-level amplitudes generate a series of multiple zeta values (MZV) the genus-one amplitudes generate a series of elliptic generalisations (“modular graph functionsâ€) that satisfy fascinating polynomial relations analogous to those satisfied by MZV’s.
The latter part of the talk will briefly review how these features fit in with the non-perturbative structure of superstring amplitudes, studied some time ago.
Posted by: QMW
Wed
1 Mar 2017
Yangian Symmetry and Integrability of Planar N=4 SYM
Niklas Beisert
(ETH Zurich)
Abstract:
This talk is about integrability of Planar N=4 super Yang-Mills theory. We present a concrete notion of the corresponding Yangian symmetry in this model, show that it holds true, and discuss the (perturbative) implications for correlation functions and Wilson loops.
This talk is about integrability of Planar N=4 super Yang-Mills theory. We present a concrete notion of the corresponding Yangian symmetry in this model, show that it holds true, and discuss the (perturbative) implications for correlation functions and Wilson loops.
Posted by: QMW
February 2017
Wed
22 Feb 2017
T-duality and the Gerbe in C-spaces
📍 London
Georgios Papadopoulos
(King's College London)
Abstract:
I shall review proposals that have been made to patch doubled spaces and explain the difficulties that arise in an effort to achieve consistent patching. Then I shall propose a scheme based on C-spaces that leads to a consistent patching but requires additional coordinates to those of doubled spaces. The T-dual pairs are identified as subspaces of the gerbe in C-spaces. The talk is based
on work done with Paul Howe, arXiv:1612.07968 [hep-th].
I shall review proposals that have been made to patch doubled spaces and explain the difficulties that arise in an effort to achieve consistent patching. Then I shall propose a scheme based on C-spaces that leads to a consistent patching but requires additional coordinates to those of doubled spaces. The T-dual pairs are identified as subspaces of the gerbe in C-spaces. The talk is based
on work done with Paul Howe, arXiv:1612.07968 [hep-th].
Posted by: KCL
Wed
22 Feb 2017
Polygon Seminar: E Theory
Peter West
(King's College London)
Abstract:
I review the theory of non-linear realisations and Kac-Moody algebras, I explain how to construct the non-linear realisation based on the Kac-Moody algebra \(E_{11}\) and its vector representation. I explain how this field theory leads to dynamical equations which contain an infinite number of fields defined on a spacetime with an infinite number of coordinates. I then show that these unique dynamical equations, when truncated to low level fields and the usual coordinates of spacetime, lead to precisely the equations of motion of eleven dimensional supergravity theory. By taking different group decompositions of \(E_{11}\) we find all the maximal supergravity theories, including the gauged maximal supergravities, and as a result the non-linear realisation is a unified theory that is the low energy effective action for type II strings and branes. These results essentially confirm the \(E_{11}\) conjecture given many years ago.
I review the theory of non-linear realisations and Kac-Moody algebras, I explain how to construct the non-linear realisation based on the Kac-Moody algebra \(E_{11}\) and its vector representation. I explain how this field theory leads to dynamical equations which contain an infinite number of fields defined on a spacetime with an infinite number of coordinates. I then show that these unique dynamical equations, when truncated to low level fields and the usual coordinates of spacetime, lead to precisely the equations of motion of eleven dimensional supergravity theory. By taking different group decompositions of \(E_{11}\) we find all the maximal supergravity theories, including the gauged maximal supergravities, and as a result the non-linear realisation is a unified theory that is the low energy effective action for type II strings and branes. These results essentially confirm the \(E_{11}\) conjecture given many years ago.
Posted by: IC
Thu
16 Feb 2017
TBA
Dhritiman Nandan
(Humboldt)
Wed
15 Feb 2017
RG boundaries and interfaces in Ising field theory
📍 London
Anatoly Konechny
(Heriot Watt University)
Abstract:
Perturbing a CFT by a relevant operator on a half space and letting the perturbation flow to the far infrared we obtain an RG interface between the UV and IR CFTs. If the IR CFT is trivial we obtain an RG boundary condition. The space of massive perturbations thus breaks up into regions labelled by conformal boundary conditions of the UV fixed point. For the 2D critical Ising model perturbed by a generic relevant operator we find the assignment of RG boundary conditions to all flows. We use some analytic results but mostly rely on TCSA and TFFSA numerical techniques. We investigate real as well as imaginary values of the magnetic field and, in particular, the RG trajectory that ends at the Yang-Lee CFT. We argue that the RG interface in the latter case does not approach a single conformal interface but rather exhibits oscillatory non-convergent behaviour.
Perturbing a CFT by a relevant operator on a half space and letting the perturbation flow to the far infrared we obtain an RG interface between the UV and IR CFTs. If the IR CFT is trivial we obtain an RG boundary condition. The space of massive perturbations thus breaks up into regions labelled by conformal boundary conditions of the UV fixed point. For the 2D critical Ising model perturbed by a generic relevant operator we find the assignment of RG boundary conditions to all flows. We use some analytic results but mostly rely on TCSA and TFFSA numerical techniques. We investigate real as well as imaginary values of the magnetic field and, in particular, the RG trajectory that ends at the Yang-Lee CFT. We argue that the RG interface in the latter case does not approach a single conformal interface but rather exhibits oscillatory non-convergent behaviour.
Posted by: KCL
Wed
15 Feb 2017
The holographic Weyl semi-metal
Karl Landsteiner
(Madrid, IFT)
Abstract:
Weyl semi-metals are an exciting new class of 3D materials with exotic transport properties. They are characterised by point like singularities in the Brillouin zone at which conduction and valence bands touch. Around these points the electronic quasi-particle excitations can be described by either left- or right-handed Weyl spinors. This makes high energy physics to be the low energy electronics of these materials. Holographic models might be useful in two ways: first some Weyl semi-metals might be strongly interacting and second holography is our best tool to understand and discover new exotic transport properties related to the chiral nature of the charge carriers, especially to chiral
anomalies. I will review the construction of a holographic model supporting a topological quantum phase transition between a topological Weyl semi-metal phase and a trivial phase and use it to predict the existence of a new dissipation less form of viscosity (Hall viscosity)
in the quantum critical region.
Weyl semi-metals are an exciting new class of 3D materials with exotic transport properties. They are characterised by point like singularities in the Brillouin zone at which conduction and valence bands touch. Around these points the electronic quasi-particle excitations can be described by either left- or right-handed Weyl spinors. This makes high energy physics to be the low energy electronics of these materials. Holographic models might be useful in two ways: first some Weyl semi-metals might be strongly interacting and second holography is our best tool to understand and discover new exotic transport properties related to the chiral nature of the charge carriers, especially to chiral
anomalies. I will review the construction of a holographic model supporting a topological quantum phase transition between a topological Weyl semi-metal phase and a trivial phase and use it to predict the existence of a new dissipation less form of viscosity (Hall viscosity)
in the quantum critical region.
Posted by: IC
Tue
14 Feb 2017
M-theory Branes for City Folk
Neil Lambert
(King's)
Abstract:
I will discuss some novel algebraic structures and how they lead to the quantum field theories that arise on the world volumes of 2-branes and 5-branes in M-theory.
I will discuss some novel algebraic structures and how they lead to the quantum field theories that arise on the world volumes of 2-branes and 5-branes in M-theory.
Posted by: KCL
Thu
9 Feb 2017
Generalized type II supergravity from kappa symmetry
Linus Wulff
(Imperial)
Abstract:
It has been known since the 80's that the Green-Schwarz superstring possesses the fermionic kappa symmetry, required for the consistency of the formulation, if the target space is a solution of the supergravity equations of motion. However, contrary to the standard lore and previous claims in the literature, it was recently shown that the converse is not true. Kappa symmetry of the Green-Schwarz superstring implies only a weaker set of equations for the target space fields, which we refer to as generalized supergravity equations. I will describe these equations for the type II case and contrast them with the standard type II supergravity equations which arise as a special case.
It has been known since the 80's that the Green-Schwarz superstring possesses the fermionic kappa symmetry, required for the consistency of the formulation, if the target space is a solution of the supergravity equations of motion. However, contrary to the standard lore and previous claims in the literature, it was recently shown that the converse is not true. Kappa symmetry of the Green-Schwarz superstring implies only a weaker set of equations for the target space fields, which we refer to as generalized supergravity equations. I will describe these equations for the type II case and contrast them with the standard type II supergravity equations which arise as a special case.
Posted by: QMW
Wed
8 Feb 2017
Integrable quantum field theories and von Neumann algebras
📍 London
Gandalf Lechner
(Cardiff University)
Abstract:
In this talk, I will report on a research programme that addresses the problem of constructing integrable relativistic quantum field theories on two-dimensional Minkowski space from their two-body S-matrix. The aims of this programme are thus identical to the form factor programme, but the tools are different: Instead of concentrating on a perturbative construction of the correlation functions of local fields, we construct a pair of "semi-local" quantum fields and use operator-algebraic tools to study local fields/observables. This leads to a construction of many models, including the Sinh-Gordon model. As another prominent example, I will also report on the status of the O(N) sigma models within this setting.
In this talk, I will report on a research programme that addresses the problem of constructing integrable relativistic quantum field theories on two-dimensional Minkowski space from their two-body S-matrix. The aims of this programme are thus identical to the form factor programme, but the tools are different: Instead of concentrating on a perturbative construction of the correlation functions of local fields, we construct a pair of "semi-local" quantum fields and use operator-algebraic tools to study local fields/observables. This leads to a construction of many models, including the Sinh-Gordon model. As another prominent example, I will also report on the status of the O(N) sigma models within this setting.
Posted by: KCL
Wed
8 Feb 2017
Semiclassics, Goldstone Bosons and CFT data
Alexander Monin
(Ecole Polytechnique, Lausanne)
Abstract:
In a generic CFT the spectrum of operators carrying a large U(1) charge can be analyzed semiclassically in an expansion in inverse powers of the charge. The key is the operator state correspondence by which such operators are associated with a finite density superfluid phase for the theory quantized on the cylinder. The dynamics is dominated by the corresponding Goldstone hydrodynamic mode and the derivative expansion coincides with the inverse charge expansion. I will illustrate this situation by first considering simple quantum mechanical analogues and then will systematize the approach by employing the coset construction for non-linearly realized space-time symmetries. Focussing on CFT3 I will illustrate that the three point function coefficients turn out to satisfy universal scaling laws and correlations as the charge and spin are varied.
In a generic CFT the spectrum of operators carrying a large U(1) charge can be analyzed semiclassically in an expansion in inverse powers of the charge. The key is the operator state correspondence by which such operators are associated with a finite density superfluid phase for the theory quantized on the cylinder. The dynamics is dominated by the corresponding Goldstone hydrodynamic mode and the derivative expansion coincides with the inverse charge expansion. I will illustrate this situation by first considering simple quantum mechanical analogues and then will systematize the approach by employing the coset construction for non-linearly realized space-time symmetries. Focussing on CFT3 I will illustrate that the three point function coefficients turn out to satisfy universal scaling laws and correlations as the charge and spin are varied.
Posted by: IC
Thu
2 Feb 2017
Localised Black Holes and Precision Holography
Jorge Santos
(DAMTP)
Abstract:
We numerically construct asymptotically global AdS_5 x S^5 black holes that are localised on the S^5. These are solutions to type IIB supergravity with S^8 horizon topology that dominate the microcanonical ensemble at small energies. At higher energies, there is a first-order phase transition to AdS_5-Schwarzschild x S^5. By the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence, this transition is dual to spontaneously breaking the SO(6) R-symmetry of N=4 supersymmetric Yang-Mills down to SO(5). We extrapolate the location of this phase transition and compute the expectation value of a scalar operator in the low energy phase. In addition, we discuss the construction of localised black holes in type IIA, which are dual (via T-duality) to the low temperature phase of thermal 1+1 dimensional supersymmetric Yang-Mills theory on a circle.
We numerically construct asymptotically global AdS_5 x S^5 black holes that are localised on the S^5. These are solutions to type IIB supergravity with S^8 horizon topology that dominate the microcanonical ensemble at small energies. At higher energies, there is a first-order phase transition to AdS_5-Schwarzschild x S^5. By the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence, this transition is dual to spontaneously breaking the SO(6) R-symmetry of N=4 supersymmetric Yang-Mills down to SO(5). We extrapolate the location of this phase transition and compute the expectation value of a scalar operator in the low energy phase. In addition, we discuss the construction of localised black holes in type IIA, which are dual (via T-duality) to the low temperature phase of thermal 1+1 dimensional supersymmetric Yang-Mills theory on a circle.
Posted by: IC
Thu
2 Feb 2017
Particle formation and ordering in strongly correlated systems: a 1+1D model of QCD
Gabor Takacs
(Budapest U.)
Abstract:
I present the results of a study of a (1 +1 )-dimensional version of the
famous Nambu-Jona-Lasinio model of quantum chromodynamics both at zero
and at finite baryon density. For zero chemical potential, we found the
formation of fermionic (nucleons and Δ baryons) and bosonic (two-quark
mesons, six-quark deuterons) excitations, and demonstrated the existence
of a phase transition. For a finite baryon density the model has a rich
phase diagram which includes phases with a density wave and superfluid
quasi-long-range (QLR) order, as well as a phase of a baryon
Tomonaga-Luttinger liquid (strange metal).
Relevant publication:
P. Azaria, R.M. Konik, Ph. Lecheminant, T. Pálmai, G. Takács and A.M.
Tsvelik:
Particle Formation and Ordering in Strongly Correlated Fermionic
Systems: Solving a Model of Quantum Chromodynamics, Phys. Rev. D94
(2016) 045003, arXiv:1601.02979 [hep-th].
I present the results of a study of a (1 +1 )-dimensional version of the
famous Nambu-Jona-Lasinio model of quantum chromodynamics both at zero
and at finite baryon density. For zero chemical potential, we found the
formation of fermionic (nucleons and Δ baryons) and bosonic (two-quark
mesons, six-quark deuterons) excitations, and demonstrated the existence
of a phase transition. For a finite baryon density the model has a rich
phase diagram which includes phases with a density wave and superfluid
quasi-long-range (QLR) order, as well as a phase of a baryon
Tomonaga-Luttinger liquid (strange metal).
Relevant publication:
P. Azaria, R.M. Konik, Ph. Lecheminant, T. Pálmai, G. Takács and A.M.
Tsvelik:
Particle Formation and Ordering in Strongly Correlated Fermionic
Systems: Solving a Model of Quantum Chromodynamics, Phys. Rev. D94
(2016) 045003, arXiv:1601.02979 [hep-th].
Posted by: QMW
Wed
1 Feb 2017
String Fluctuations in Non-Conformal Holography
Kostya Zarembo
(NORDITA)
Abstract:
Quantum fluctuations of the string worldsheet lead to important effects in gauge-string duality. One example is the Lüscher term is the QQ-bar potential in QCD, important for matching the lattice data.
I will discuss non-conformal holography of the N=2* theory which provides a controllable setup where the effects of string fluctuations are explicitly calculable in field theory, using localization, even though the problem is intrinsically strongly-coupled. The results obtained by direct quantization of the dual string theory perfectly match the field-theory predictions, after subtle effects like dilaton coupling to the string worldsheet are properly taken into account.
Quantum fluctuations of the string worldsheet lead to important effects in gauge-string duality. One example is the Lüscher term is the QQ-bar potential in QCD, important for matching the lattice data.
I will discuss non-conformal holography of the N=2* theory which provides a controllable setup where the effects of string fluctuations are explicitly calculable in field theory, using localization, even though the problem is intrinsically strongly-coupled. The results obtained by direct quantization of the dual string theory perfectly match the field-theory predictions, after subtle effects like dilaton coupling to the string worldsheet are properly taken into account.
Posted by: KCL
Wed
1 Feb 2017
Probing the black hole interior in AdS/CFT
Kyriakos Papadodimas
(CERN)
Abstract:
I will review recent developments related to the holographic
reconstruction of the black hole interior in AdS/CFT and I will discuss the implications for the black hole information paradox.
I will review recent developments related to the holographic
reconstruction of the black hole interior in AdS/CFT and I will discuss the implications for the black hole information paradox.
Posted by: KCL
January 2017
Thu
26 Jan 2017
Cosmic Inflation from String Axions
Susha Parameswaran
(University of Liverpool)
Abstract:
An early epoch of cosmic inflation, driven by a scalar field slowly rolling down a flat potential, provides an elegant solution to several cosmological puzzles. The notorious sensitivity of the slow roll potential to quantum gravity effects, presents both a challenge and opportunity for string theory to connect to observations.
A very promising way to explain slow roll inflation is with an axionic inflaton field, whose flat potential is protected by a perturbative shift symmetry. However, the canonical models of axion inflation - "Natural Inflation" and "Axion Monodromy" - are now both in tension with observations and difficult to embed in a UV complete theory like string theory. I will discuss these challenges, and also a way to overcome them, with an inflationary mechanism - beyond slow roll - that is well-motivated from string theory and consistent with observations, including distinctive signatures to be searched for in future observations.
An early epoch of cosmic inflation, driven by a scalar field slowly rolling down a flat potential, provides an elegant solution to several cosmological puzzles. The notorious sensitivity of the slow roll potential to quantum gravity effects, presents both a challenge and opportunity for string theory to connect to observations.
A very promising way to explain slow roll inflation is with an axionic inflaton field, whose flat potential is protected by a perturbative shift symmetry. However, the canonical models of axion inflation - "Natural Inflation" and "Axion Monodromy" - are now both in tension with observations and difficult to embed in a UV complete theory like string theory. I will discuss these challenges, and also a way to overcome them, with an inflationary mechanism - beyond slow roll - that is well-motivated from string theory and consistent with observations, including distinctive signatures to be searched for in future observations.
Posted by: QMW
Wed
25 Jan 2017
AdS crunches from relevant deformations of CFTs
📍 London
Prem Kumar
(Swansea)
Abstract:
We discuss examples of relevant deformations of known CFTs placed in de Sitter spacetime, possessing AdS gravity duals with Big Crunch singularities. We point out generic aspects of such dual backgrounds, including the behaviour in the vicinity of the singularity, holographic correlators in the geodesic approximation, and retarded correlators in an analytically tractable example within the AdS_4/CFT_3 context. We briefly describe an attempt to characterise the bulk crunch and its putative resolution within the O(N) vector model in 3D.
We discuss examples of relevant deformations of known CFTs placed in de Sitter spacetime, possessing AdS gravity duals with Big Crunch singularities. We point out generic aspects of such dual backgrounds, including the behaviour in the vicinity of the singularity, holographic correlators in the geodesic approximation, and retarded correlators in an analytically tractable example within the AdS_4/CFT_3 context. We briefly describe an attempt to characterise the bulk crunch and its putative resolution within the O(N) vector model in 3D.
Posted by: KCL
Wed
25 Jan 2017
Universal Formula for the Holographic Speed of Sound
Andres Anabalon
(Adolfo Ibanez U.)
Abstract:
We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner-Freedman window. We show that is possible to derive a universal formula for the speed of sound for any theory. As an example we find all the planar black holes of the single scalar field consistent truncation of type IIB that preserves the SO(3)×SO(3) R-symmetry group of the gauge theory. We find the speed of sound for different values of the induced vacuum expectation value when a double trace deformation is induced in the gauge theory. For any theory, we show that the speed of sound is not bounded by any special value.
We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner-Freedman window. We show that is possible to derive a universal formula for the speed of sound for any theory. As an example we find all the planar black holes of the single scalar field consistent truncation of type IIB that preserves the SO(3)×SO(3) R-symmetry group of the gauge theory. We find the speed of sound for different values of the induced vacuum expectation value when a double trace deformation is induced in the gauge theory. For any theory, we show that the speed of sound is not bounded by any special value.
Posted by: IC
Tue
24 Jan 2017
Matrix models for the gauge-gravity correspondence
Nadav Drukker
(King's)
Abstract:
The gauge-gravity correspondence identifies a field theory with a gravitational theory. The gravitational theory is weakly coupled when the field theory has large coupling and vice versa, which mostly prevents matching nontrivial results between the two descriptions. I will discuss cases when the field theory calculation can be reduced to a finite dimensional matrix integral, representing some counting problems. I will then evaluate the integral exactly and reexpand the exact result, which is valid for all coupling, at strong coupling. The resulting expression should match a weak coupling gravitational (or string theoretic) calculation and I’ll comment on what is known from that direction.
The gauge-gravity correspondence identifies a field theory with a gravitational theory. The gravitational theory is weakly coupled when the field theory has large coupling and vice versa, which mostly prevents matching nontrivial results between the two descriptions. I will discuss cases when the field theory calculation can be reduced to a finite dimensional matrix integral, representing some counting problems. I will then evaluate the integral exactly and reexpand the exact result, which is valid for all coupling, at strong coupling. The resulting expression should match a weak coupling gravitational (or string theoretic) calculation and I’ll comment on what is known from that direction.
Posted by: KCL
Thu
19 Jan 2017
6d Dual Conformal Symmetry and Minimal Volumes in AdS
Arthur Lipstein
(Durham)
Abstract:
The planar scattering amplitudes of 4d N = 4 super Yang-Mills theory and 3d N=6 Chern-Simons theory exhibit a remarkable property known as dual conformal symmetry. Motivated by this, we investigate the consequences of dual conformal symmetry in six dimensions. We find that 6d dual conformal symmetry fixes the structure of the one-loop 4-point amplitude and suggests a Lagrangian with more than two derivatives. Moreover, we obtain a similar structure by generalizing the Alday-Maldacena solution for a string in Anti-de Sitter space to a 2-brane ending on a pillow-shaped surface in the boundary whose seams correspond to a null-polygon, which suggests an all-loop formula for the 4-point amplitude similar to that of N=4 super Yang-Mills theory.
The planar scattering amplitudes of 4d N = 4 super Yang-Mills theory and 3d N=6 Chern-Simons theory exhibit a remarkable property known as dual conformal symmetry. Motivated by this, we investigate the consequences of dual conformal symmetry in six dimensions. We find that 6d dual conformal symmetry fixes the structure of the one-loop 4-point amplitude and suggests a Lagrangian with more than two derivatives. Moreover, we obtain a similar structure by generalizing the Alday-Maldacena solution for a string in Anti-de Sitter space to a 2-brane ending on a pillow-shaped surface in the boundary whose seams correspond to a null-polygon, which suggests an all-loop formula for the 4-point amplitude similar to that of N=4 super Yang-Mills theory.
Posted by: IC
Wed
18 Jan 2017
Space-time CFTs from the Riemann sphere
📍 London
Tim Adamo
(Imperial College)
Abstract:
In recent years, there has been significant process in the study of perturbative field theory scattering amplitudes using certain 2d chiral, first-order CFTs known as 'ambitwistor string theories.' After a brief review of the ambitwistor setup, I will introduce a related family of 2d CFTs, which can be viewed as constrained ambitwistor strings. These new models describe holomorphic maps from the Riemann sphere to the projective null cone in D-dimensional Minkowski space. This target space is the natural setting to describe field theories with (classical) conformal invariance in (D-2)-dimensions. Killing the anomalies associated with these models fixes critical dimensions for which three well-known space-time field theories (bi-adjoint cubic scalar, gauge theory, gravity) are conformal. Furthermore, the spectrum of each model contains all single field insertions, along with their conformal descendants, of the correct scaling dimension. Time permitting, I will also outline how the space-time 3-point functions can be obtained from the 3-point correlators on the Riemann sphere.
In recent years, there has been significant process in the study of perturbative field theory scattering amplitudes using certain 2d chiral, first-order CFTs known as 'ambitwistor string theories.' After a brief review of the ambitwistor setup, I will introduce a related family of 2d CFTs, which can be viewed as constrained ambitwistor strings. These new models describe holomorphic maps from the Riemann sphere to the projective null cone in D-dimensional Minkowski space. This target space is the natural setting to describe field theories with (classical) conformal invariance in (D-2)-dimensions. Killing the anomalies associated with these models fixes critical dimensions for which three well-known space-time field theories (bi-adjoint cubic scalar, gauge theory, gravity) are conformal. Furthermore, the spectrum of each model contains all single field insertions, along with their conformal descendants, of the correct scaling dimension. Time permitting, I will also outline how the space-time 3-point functions can be obtained from the 3-point correlators on the Riemann sphere.
Posted by: KCL
Wed
18 Jan 2017
Holographic Entanglement Entropy for the Gravitational Anomaly in Four Dimensions
Jeff Murugan
(Cape Town U.)
Abstract:
We compute the holographic entanglement entropy for the pure gravitational anomaly in 3+1 dimensions. Using the perturbative method developed for com- puting entanglement entropy for quantum field theories, we also compute the parity odd contribution to the entanglement entropy of the dual field theory that comes from a background gravitational Chern-Simons term. We find that, in leading order in the perturbation of the background geometry, the two contribu- tions match except for a logarithmic divergent term on the field theory side. We interpret this extra contribution as encoding our ignorance of the source which creates the perturbation of the geometry.
We compute the holographic entanglement entropy for the pure gravitational anomaly in 3+1 dimensions. Using the perturbative method developed for com- puting entanglement entropy for quantum field theories, we also compute the parity odd contribution to the entanglement entropy of the dual field theory that comes from a background gravitational Chern-Simons term. We find that, in leading order in the perturbation of the background geometry, the two contribu- tions match except for a logarithmic divergent term on the field theory side. We interpret this extra contribution as encoding our ignorance of the source which creates the perturbation of the geometry.
Posted by: QMW
Thu
12 Jan 2017
South East Mathematical Physics seminar
Allday Event
(Kent)
Abstract:
All day event: speakers include Andrea Fontanella (Surrey), Ana Loureiro (Kent), Marika Taylor (Southampton) and Takato Yoshimura (King's College).
Details:
https://www.kent.ac.uk/smsas/personal/tcd/webpages/MP/semps7.htm
All day event: speakers include Andrea Fontanella (Surrey), Ana Loureiro (Kent), Marika Taylor (Southampton) and Takato Yoshimura (King's College).
Details:
https://www.kent.ac.uk/smsas/personal/tcd/webpages/MP/semps7.htm
Posted by: KCL
Thu
12 Jan 2017
Poincare' symmetry shapes the massive 3-point amplitude
Andrea Marzolla
(Bruxelles U.)
Abstract:
Poincaré invariance imposes strong non-perturbative constraints on the dependence of scattering amplitudes on the kinematical variables. For massless external states, Benincasa and Cachazo have shown that the 3-point amplitude is fully determined up to a constant (the coupling). We extend their approach, based on the spinor-helicity formalism, to time-like momenta, and we find that, even when massive external states are involved, the functional form of the 3-point amplitude is fully determined, up to (several) constants.
In this talk I review the derivation in the massless case, enlightening the role of the little group covariance of the amplitude in constraining its functional form, and the particularly simple form that these constraints get in the spinor language. Then I will show how to extend this procedure to the massive case, deriving the constraining equations for the massive little group, and eventually showing the expressions for 3-point amplitudes involving one, two, or three massive particles.
Poincaré invariance imposes strong non-perturbative constraints on the dependence of scattering amplitudes on the kinematical variables. For massless external states, Benincasa and Cachazo have shown that the 3-point amplitude is fully determined up to a constant (the coupling). We extend their approach, based on the spinor-helicity formalism, to time-like momenta, and we find that, even when massive external states are involved, the functional form of the 3-point amplitude is fully determined, up to (several) constants.
In this talk I review the derivation in the massless case, enlightening the role of the little group covariance of the amplitude in constraining its functional form, and the particularly simple form that these constraints get in the spinor language. Then I will show how to extend this procedure to the massive case, deriving the constraining equations for the massive little group, and eventually showing the expressions for 3-point amplitudes involving one, two, or three massive particles.
Posted by: QMW