Triangle Seminars
August 2019
Wed
14 Aug 2019
Traversable wormholes in four dimensions
Iva Lovrekovic
(Imperial College)
Abstract:
I will talk about the recent quite interesting article by Maldacena, in which he writes on the subject of the traversable wormholes. The most interesting thing that needs to be pointed out here are the way that wormholes are stabilised without the addition of the exotic matter while the theory that describes them is still Einstein gravity, with Maxwell theory and charged massless fermion, since wormholes without the addition of the exotic matter have been known in the higher derivative theories. The wormhole is made possible by fermions that give rise to negative Casimir-like energy and by being a long wormhole which does not lead to causality violations.
https://arxiv.org/abs/1807.04726
I will talk about the recent quite interesting article by Maldacena, in which he writes on the subject of the traversable wormholes. The most interesting thing that needs to be pointed out here are the way that wormholes are stabilised without the addition of the exotic matter while the theory that describes them is still Einstein gravity, with Maxwell theory and charged massless fermion, since wormholes without the addition of the exotic matter have been known in the higher derivative theories. The wormhole is made possible by fermions that give rise to negative Casimir-like energy and by being a long wormhole which does not lead to causality violations.
https://arxiv.org/abs/1807.04726
Posted by: QMW
July 2019
Thu
11 Jul 2019
Surface defects in three-dimensional topological field theory
Ingo Runkel
(Hamburg U.)
Abstract:
I would like to discuss a class of three-dimensional topological field theories called Reshetikhin-Turaev theories. Examples are Chern-Simons theories with compact gauge group. There are no point-like observables in these theories, and one typically considers line-observables, called Wilson lines. However, one can also discuss observables associated to surfaces. We will see how to describe such observables in Reshetikhin-Turaev TQFTs and look at some applications.
I would like to discuss a class of three-dimensional topological field theories called Reshetikhin-Turaev theories. Examples are Chern-Simons theories with compact gauge group. There are no point-like observables in these theories, and one typically considers line-observables, called Wilson lines. However, one can also discuss observables associated to surfaces. We will see how to describe such observables in Reshetikhin-Turaev TQFTs and look at some applications.
Posted by: QMW
June 2019
Thu
27 Jun 2019
Defects in topological and conformal field theory
๐ London
Two day meeting Thursday and Friday
(For speakers, see the website)
Abstract:
This is a two day meeting, please see <a href="https://www.nms.kcl.ac.uk/gerard.watts/Def19/index.html">the website</a>
for details.
<a href="https://www.nms.kcl.ac.uk/gerard.watts/Def19/index.html">www.tinyurl.com/kcldef19</a>
Registration is required as King's has a new policy on attendance.
Supported by the LMS and the IoP
This is a two day meeting, please see <a href="https://www.nms.kcl.ac.uk/gerard.watts/Def19/index.html">the website</a>
for details.
<a href="https://www.nms.kcl.ac.uk/gerard.watts/Def19/index.html">www.tinyurl.com/kcldef19</a>
Registration is required as King's has a new policy on attendance.
Supported by the LMS and the IoP
Posted by: KCL
Wed
26 Jun 2019
The entropy of bulk quantum fields and the entanglement wedge of an evaporating black hole
Henry Maxfield
(UCSB)
Abstract:
Semiclassical gravity is famously in tension with the unitary evolution of quantum mechanics when black holes evaporate. I'll describe a semiclassical calculation that nonetheless reproduces signatures of unitarity, namely the "Page curve" of entropy and the Hayden-Preskill protocol. This involves finding a quantum extremal surface, an extremum of the generalised entropy (the area in Planck units plus the entropy of exterior matter), which in the context of an evaporating black hole can exist far from a classical extremal surface. The calculations are performed in an exactly solvable model of Jackiw-Teitelboim gravity coupled to conformal matter. I will conclude by commenting and speculating on the implications for the information paradox.
Semiclassical gravity is famously in tension with the unitary evolution of quantum mechanics when black holes evaporate. I'll describe a semiclassical calculation that nonetheless reproduces signatures of unitarity, namely the "Page curve" of entropy and the Hayden-Preskill protocol. This involves finding a quantum extremal surface, an extremum of the generalised entropy (the area in Planck units plus the entropy of exterior matter), which in the context of an evaporating black hole can exist far from a classical extremal surface. The calculations are performed in an exactly solvable model of Jackiw-Teitelboim gravity coupled to conformal matter. I will conclude by commenting and speculating on the implications for the information paradox.
Posted by: IC
Thu
13 Jun 2019
Heterotic and Bosonic String Amplitudes from Scattering Equations
Fei Teng
(Uppsala University)
Abstract:
In this talk, I will connect, via tree-level double copy, any massless string amplitudes with QFT amplitudes given by Cachazo-He-Yuan (CHY) formula. This can be derived by a detailed study of integration-by-part (IBP) reduction of string integrands. As an application, we consider general multitrace integrands of heterotic string amplitudes. The new technology generates a recursive expansion of the heterotic string amplitudes in terms of those with fewer gravitons and traces, where the kinematic coefficients are building blocks for BCJ numerators of the (DF)^2+YM+phi^3 theory. Finally, we give a generic CHY integrand for multitrace (DF)^2+YM+phi^3 amplitudes, which reproduce the corresponding heterotic string amplitudes after double copy with a single-valued Z-theory.
In this talk, I will connect, via tree-level double copy, any massless string amplitudes with QFT amplitudes given by Cachazo-He-Yuan (CHY) formula. This can be derived by a detailed study of integration-by-part (IBP) reduction of string integrands. As an application, we consider general multitrace integrands of heterotic string amplitudes. The new technology generates a recursive expansion of the heterotic string amplitudes in terms of those with fewer gravitons and traces, where the kinematic coefficients are building blocks for BCJ numerators of the (DF)^2+YM+phi^3 theory. Finally, we give a generic CHY integrand for multitrace (DF)^2+YM+phi^3 amplitudes, which reproduce the corresponding heterotic string amplitudes after double copy with a single-valued Z-theory.
Posted by: QMW
Wed
12 Jun 2019
Euclidean Wormholes and Holography
Panos Betzios
(Crete)
Abstract:
In this talk I will discuss asymptotically AdS wormhole solutions in the
context of holography.
I will present how to compute correlation functions of local operators
as well as non local observables such as correlation functions of Wilson
loops on the distinct boundaries and I will discuss their behavior.
Moreover, I will discuss the effect that multi-trace deformations have
on such observables.
From the computations mentioned we observe that the dual theory is
expected to be described in terms of two interacting sectors coupled by
a
UV soft, non-local interaction.
Finally, I will present a simple effective field theory construction
that can
explain the behaviors that we observe from these gravitational
computations.
In this talk I will discuss asymptotically AdS wormhole solutions in the
context of holography.
I will present how to compute correlation functions of local operators
as well as non local observables such as correlation functions of Wilson
loops on the distinct boundaries and I will discuss their behavior.
Moreover, I will discuss the effect that multi-trace deformations have
on such observables.
From the computations mentioned we observe that the dual theory is
expected to be described in terms of two interacting sectors coupled by
a
UV soft, non-local interaction.
Finally, I will present a simple effective field theory construction
that can
explain the behaviors that we observe from these gravitational
computations.
Posted by: IC
Wed
12 Jun 2019
Eikonal phase shift in AdS black holes vs multi-stress-tensor OPEs in holographic CFT
Gim Seng Ng
(Trinity College Dublin)
Abstract:
We study the leading and next-to-leading eikonal phase in the context of AdS/CFT. In the bulk side, we compute the phase shift of a highly energetic particle traveling in the background of an asymptotically AdS black hole. In the dual CFT, the phase shift is related to a four point function in the Regge limit. The black hole mass is translated to the ratio between the conformal dimension of a heavy operator and the central charge. This ratio serves as a useful
expansion parameter; its power measures the number of stress tensors appearing in the intermediate channel.
The leading eikonal phase shift in 4d holographic CFTs can be computed using conformal Regge theory while the computation of the next-to-leading order eikonal phase shift relies on a new universal formula for the lowest-twist OPE of double-trace stress-tensors with two scalar operators. These OPE coefficients are consistent with the second-order phase shift as well as anomalous dimensions obtained in AdS black holes in the lightcone limit. In relations to the
idea of รขโฌลeikonalizationรขโฌย of the stress-tensor sector in holographic CFTs, we comment on hints of a structure similar to the vacuum Virasoro block in 2d CFT.
We study the leading and next-to-leading eikonal phase in the context of AdS/CFT. In the bulk side, we compute the phase shift of a highly energetic particle traveling in the background of an asymptotically AdS black hole. In the dual CFT, the phase shift is related to a four point function in the Regge limit. The black hole mass is translated to the ratio between the conformal dimension of a heavy operator and the central charge. This ratio serves as a useful
expansion parameter; its power measures the number of stress tensors appearing in the intermediate channel.
The leading eikonal phase shift in 4d holographic CFTs can be computed using conformal Regge theory while the computation of the next-to-leading order eikonal phase shift relies on a new universal formula for the lowest-twist OPE of double-trace stress-tensors with two scalar operators. These OPE coefficients are consistent with the second-order phase shift as well as anomalous dimensions obtained in AdS black holes in the lightcone limit. In relations to the
idea of รขโฌลeikonalizationรขโฌย of the stress-tensor sector in holographic CFTs, we comment on hints of a structure similar to the vacuum Virasoro block in 2d CFT.
Posted by: QMW
Mon
10 Jun 2019
Conformal block, Crossing Kernel and Multi-variable Hypergeometric Functions
Heng-Yu Chen
(National Taiwan University)
Abstract:
In this talk, based on the work to appear, we present an alternative representation of the conformal block with external scalars in general spacetime dimensions in terms of a finite summation over Appell fourth hypergeometric function, and its generalization to the primary operator exchange with continuous spin which is relevant for Lorentzian spacetime. Using these results we apply the Lorentzian inversion formula to compute so-called crossing kernel in general spacetime dimensions, and the result can be written as a double infinite summation over certain Kempe de Feriet hypergeometric functions. During the talk, we will introduce various physical quantities and discuss their subtitles and applications.
In this talk, based on the work to appear, we present an alternative representation of the conformal block with external scalars in general spacetime dimensions in terms of a finite summation over Appell fourth hypergeometric function, and its generalization to the primary operator exchange with continuous spin which is relevant for Lorentzian spacetime. Using these results we apply the Lorentzian inversion formula to compute so-called crossing kernel in general spacetime dimensions, and the result can be written as a double infinite summation over certain Kempe de Feriet hypergeometric functions. During the talk, we will introduce various physical quantities and discuss their subtitles and applications.
Posted by: oxford
Thu
6 Jun 2019
From the convergence and resummation of all-order hydrodynamics to quantum chaos
Saso Grozdanov
(MIT)
Abstract:
Hydrodynamic excitations corresponding to sound and diffusive modes in fluids are characterised by gapless dispersion relations. In the hydrodynamic gradient expansion, their frequencies are represented by infinite power series in spatial momenta. I will discuss how the introduction of a new concept of the hydrodynamic complex spectral curve in the space of complexified frequency and spatial momentumรขโฌโthe concept otherwise known from algebraic geometry–-can be used to prove general properties about hydrodynamics, including its finite radius of convergence. When the infinite series are resummed, they exhibit a fascinating, recently-discovered phenomenon of pole-skipping, which enables us to analyse the underlying, microscopic quantum many-body chaos in the system. Throughout my talk, I will use gauge-gravity duality as a tool to explicitly show these phenomena in holographic systems and discuss what their implications are for the dual gravity theory.
Hydrodynamic excitations corresponding to sound and diffusive modes in fluids are characterised by gapless dispersion relations. In the hydrodynamic gradient expansion, their frequencies are represented by infinite power series in spatial momenta. I will discuss how the introduction of a new concept of the hydrodynamic complex spectral curve in the space of complexified frequency and spatial momentumรขโฌโthe concept otherwise known from algebraic geometry–-can be used to prove general properties about hydrodynamics, including its finite radius of convergence. When the infinite series are resummed, they exhibit a fascinating, recently-discovered phenomenon of pole-skipping, which enables us to analyse the underlying, microscopic quantum many-body chaos in the system. Throughout my talk, I will use gauge-gravity duality as a tool to explicitly show these phenomena in holographic systems and discuss what their implications are for the dual gravity theory.
Posted by: QMW
Wed
5 Jun 2019
Black holes in N=4 Super-Yang-Mills
Francesco Benini
(SISSA)
Abstract:
AdS/CFT provides a consistent non-perturbative definition of quantum
gravity in asymptotically AdS space. Black holes should correspond to
ensembles of states in the boundary field theory. By analyzing the
superconformal index of 4d N=4 SU(N) Super-Yang-Mills, with the help
of a new Bethe Ansatz type formula, we are able to exactly reproduce
the Bekenstein-Hawking entropy of BPS black holes in AdS5 x S5. The
large N limit exhibits many competing contributions and Stokes
phenomena, hinting at new physics.
AdS/CFT provides a consistent non-perturbative definition of quantum
gravity in asymptotically AdS space. Black holes should correspond to
ensembles of states in the boundary field theory. By analyzing the
superconformal index of 4d N=4 SU(N) Super-Yang-Mills, with the help
of a new Bethe Ansatz type formula, we are able to exactly reproduce
the Bekenstein-Hawking entropy of BPS black holes in AdS5 x S5. The
large N limit exhibits many competing contributions and Stokes
phenomena, hinting at new physics.
Posted by: IC
Tue
4 Jun 2019
Bimetric theory of fractional quantum Hall states
Andrey Gromov
(Brown)
Abstract:
Fractional quantum Hall (FQH) states are topologically ordered. Additionally, FQH states support a collective neutral excitation known as the Girvin-MacDonald-Platzman (GMP) mode. Certain features of this mode are independent of the microscopic details. The objective of the talk is to construct an effective theory includes both topological properties and the massive GMP mode. The theory reproduces the universal properties of chiral lowest Landau level (LLL) FQH states which lie beyond the TQFT data, such as the projected static structure factor and the GMP algebra of area-preserving diffeomorphisms. The dynamics of the mode is described by a fluctuating rank-2 symmetric, positive-definite tensor, which leads to a natural geometric (or gravitational) interpretation of the GMP mode.
Fractional quantum Hall (FQH) states are topologically ordered. Additionally, FQH states support a collective neutral excitation known as the Girvin-MacDonald-Platzman (GMP) mode. Certain features of this mode are independent of the microscopic details. The objective of the talk is to construct an effective theory includes both topological properties and the massive GMP mode. The theory reproduces the universal properties of chiral lowest Landau level (LLL) FQH states which lie beyond the TQFT data, such as the projected static structure factor and the GMP algebra of area-preserving diffeomorphisms. The dynamics of the mode is described by a fluctuating rank-2 symmetric, positive-definite tensor, which leads to a natural geometric (or gravitational) interpretation of the GMP mode.
Posted by: IC
Mon
3 Jun 2019
Bimetric theory of fractional quantum Hall states
Andrey Gromov
(Brown U.)
Abstract:
Fractional quantum Hall (FQH) states are topologically ordered. Additionally, FQH states support a collective neutral excitation known as the Girvin-MacDonald-Platzman (GMP) mode. Certain features of this mode are independent of the microscopic details. The objective of the talk is to construct an effective theory includes both topological properties and the massive GMP mode. The theory reproduces the universal properties of chiral lowest Landau level (LLL) FQH states which lie beyond the TQFT data, such as the projected static structure factor and the GMP algebra of area-preserving diffeomorphisms. The dynamics of the mode is described by a fluctuating rank-2 symmetric, positive-definite tensor, which leads to a natural geometric (or gravitational) interpretation of the GMP mode.
Fractional quantum Hall (FQH) states are topologically ordered. Additionally, FQH states support a collective neutral excitation known as the Girvin-MacDonald-Platzman (GMP) mode. Certain features of this mode are independent of the microscopic details. The objective of the talk is to construct an effective theory includes both topological properties and the massive GMP mode. The theory reproduces the universal properties of chiral lowest Landau level (LLL) FQH states which lie beyond the TQFT data, such as the projected static structure factor and the GMP algebra of area-preserving diffeomorphisms. The dynamics of the mode is described by a fluctuating rank-2 symmetric, positive-definite tensor, which leads to a natural geometric (or gravitational) interpretation of the GMP mode.
Posted by: QMW
May 2019
Thu
30 May 2019
QMUL Seminar Cancelled
. .
Wed
29 May 2019
TBA
Chris Blair
(VUB)
Abstract:
TBA
TBA
Posted by: IC
Thu
23 May 2019
Effective Field Theories of Post-Newtonian Gravity
Michele Levi
(IPhT Saclay)
Abstract:
This talk presents the progress made in my research via the introduction of effective field theories (EFTs) into post-Newtonian (PN) gravity. These have been put forward in the context of gravitational waves (GWs) from the compact binary inspiral. The setup and the strategy of a multi-stage EFT framework, which is deployed for the PN binary inspiral problem, is outlined. I then present in more detail the study of two effective theories at the intermediate scales of the problem. First, the EFT for a single rotating compact object is considered, from which I proceed to the EFT of a compact binary system, viewed as a composite particle with internal binding interactions. I conclude with the prospects of building on the field, and using further modern field theory insights and tools, to address the study of GWs, as well as to expand our fundamental understanding of QFTs and gravity theories at all scales.
This talk presents the progress made in my research via the introduction of effective field theories (EFTs) into post-Newtonian (PN) gravity. These have been put forward in the context of gravitational waves (GWs) from the compact binary inspiral. The setup and the strategy of a multi-stage EFT framework, which is deployed for the PN binary inspiral problem, is outlined. I then present in more detail the study of two effective theories at the intermediate scales of the problem. First, the EFT for a single rotating compact object is considered, from which I proceed to the EFT of a compact binary system, viewed as a composite particle with internal binding interactions. I conclude with the prospects of building on the field, and using further modern field theory insights and tools, to address the study of GWs, as well as to expand our fundamental understanding of QFTs and gravity theories at all scales.
Posted by: QMW
Wed
22 May 2019
Little Strings, Long Strings, and Fuzzballs
Emil Martinec
(Chicago)
Abstract:
The microstate structure of AdS3 black holes involves stringy ingredients, yet quantitative control over these ingredients in a regime where the state being described approximates a black hole has been elusive. This talk will show how 2d worldsheet current algebra provides a tool to describe the stringy objects that govern the black hole phase transition in AdS3 and linear dilaton backgrounds, providing a bridge between the entropy-carrying degrees of freedom of the dual non-gravitational theory (little strings or long strings) and their conjectured gravitational dual, the fuzzball.
The microstate structure of AdS3 black holes involves stringy ingredients, yet quantitative control over these ingredients in a regime where the state being described approximates a black hole has been elusive. This talk will show how 2d worldsheet current algebra provides a tool to describe the stringy objects that govern the black hole phase transition in AdS3 and linear dilaton backgrounds, providing a bridge between the entropy-carrying degrees of freedom of the dual non-gravitational theory (little strings or long strings) and their conjectured gravitational dual, the fuzzball.
Posted by: IC
Mon
20 May 2019
All N=4 conformal supergravities
Franz Ciceri
(AEI Potsdam)
Abstract:
Supersymmetric extensions of conformal gravity have been known for a long time. In four dimensions, N=4 conformal supergravity is the maximally supersymmetric theory of this type. Although its field representation and the non-linear transformations rules were derived more than 30 years ago, no invariant action had been constructed so far. We present the most general class of actions which turns out to be characterised by a holomorphic function. This deviates from the non-maximally supersymmetric cases where the action is unique.
Meanwhile, elaborate loop computations have indicated that N=4 Poincare supergravity diverges at four loops, and the divergence is believed to be related to the presence of a potential one-loop anomaly in the duality symmetry of the theory. We argue that one of the constructed conformal actions, after gauge fixing the conformal symmetries and carefully eliminating auxiliary fields, can be used as a finite supersymmetric counterterm that cancels the anomalous contribution of the one-loop graphs in the Poincare theory.
Supersymmetric extensions of conformal gravity have been known for a long time. In four dimensions, N=4 conformal supergravity is the maximally supersymmetric theory of this type. Although its field representation and the non-linear transformations rules were derived more than 30 years ago, no invariant action had been constructed so far. We present the most general class of actions which turns out to be characterised by a holomorphic function. This deviates from the non-maximally supersymmetric cases where the action is unique.
Meanwhile, elaborate loop computations have indicated that N=4 Poincare supergravity diverges at four loops, and the divergence is believed to be related to the presence of a potential one-loop anomaly in the duality symmetry of the theory. We argue that one of the constructed conformal actions, after gauge fixing the conformal symmetries and carefully eliminating auxiliary fields, can be used as a finite supersymmetric counterterm that cancels the anomalous contribution of the one-loop graphs in the Poincare theory.
Posted by: QMW
Thu
16 May 2019
On Integrable Subsectors of AdS/CFT and LLM geometries
Jaco van Zyl
(Witwatersrand U.)
Abstract:
The 1/2 BPS and regular LLM geometries are formed from the backreaction of a large number of D-branes on AdS_5 x S^5. The dual N=4 SYM operator to this configuration, and excitations thereof, thus lie outside of the planar limit of the theory. Explicitly the operators dual to these geometries are Schur polynomials labelled by a Young diagram with O(N^2) boxes and excitations of this configuration are restricted Schur polynomials obtained by adding boxes (and restriction labels) to this diagram. A special class of these geometries are labelled by Young diagrams with O(1) well separated corners. In the large N limit excitations localised at any one of these corners only mix with each other which is a major simplification. A recent proposal has argued that the large N dynamics of these operators is isomorphic to that of planar N=4 SYM and thus represents an integrable subsector of N=4 SYM. In this talk this proposal is reviewed and aspects of the weak and strong coupling evidence presented.
The 1/2 BPS and regular LLM geometries are formed from the backreaction of a large number of D-branes on AdS_5 x S^5. The dual N=4 SYM operator to this configuration, and excitations thereof, thus lie outside of the planar limit of the theory. Explicitly the operators dual to these geometries are Schur polynomials labelled by a Young diagram with O(N^2) boxes and excitations of this configuration are restricted Schur polynomials obtained by adding boxes (and restriction labels) to this diagram. A special class of these geometries are labelled by Young diagrams with O(1) well separated corners. In the large N limit excitations localised at any one of these corners only mix with each other which is a major simplification. A recent proposal has argued that the large N dynamics of these operators is isomorphic to that of planar N=4 SYM and thus represents an integrable subsector of N=4 SYM. In this talk this proposal is reviewed and aspects of the weak and strong coupling evidence presented.
Posted by: QMW
Wed
15 May 2019
TBA
Vasileios Niarchos
(Durham)
Mon
13 May 2019
Quo Vadis: colliders?
Rohini Godbole
(Indian Institute of Science)
Abstract:
After a summary of current status of experimental results in particle physics, including the presentation of what I call the LHC paradox, I will discuss briefly how colliders were indispensible in arriving at this point of the journey. After this I would discuss what the next steps are: as to where do we go from here in the story of collider physics. If time is left, I will discuss some of the issues that the future colliders can address , by taking examples from the known unknowns, viz. in the framework of particular BSM models and also the unknown unknowns viz the model independent approach.
After a summary of current status of experimental results in particle physics, including the presentation of what I call the LHC paradox, I will discuss briefly how colliders were indispensible in arriving at this point of the journey. After this I would discuss what the next steps are: as to where do we go from here in the story of collider physics. If time is left, I will discuss some of the issues that the future colliders can address , by taking examples from the known unknowns, viz. in the framework of particular BSM models and also the unknown unknowns viz the model independent approach.
Posted by: QMW
Thu
9 May 2019
Infrared enhancement of supersymmetry in four dimensions
Simone Giacomelli
(Oxford)
Abstract:
In this seminar I will discuss a recently-found class of RG flows in four dimensions exhibiting enhancement of supersymmetry in the infrared, which provides a lagrangian description of several strongly-coupled N=2 SCFTs. The procedure involves starting from a N=2 SCFT, coupling a chiral multiplet in the adjoint representation of the global symmetry to the moment map of the SCFT and turning on a nilpotent expectation value for this chiral. We show that, combining considerations based on 't Hooft anomaly matching and basic results about the N=2 superconformal algebra, it is possible to understand in detail the mechanism underlying this phenomenon and formulate a simple criterion for supersymmetry enhancement.
In this seminar I will discuss a recently-found class of RG flows in four dimensions exhibiting enhancement of supersymmetry in the infrared, which provides a lagrangian description of several strongly-coupled N=2 SCFTs. The procedure involves starting from a N=2 SCFT, coupling a chiral multiplet in the adjoint representation of the global symmetry to the moment map of the SCFT and turning on a nilpotent expectation value for this chiral. We show that, combining considerations based on 't Hooft anomaly matching and basic results about the N=2 superconformal algebra, it is possible to understand in detail the mechanism underlying this phenomenon and formulate a simple criterion for supersymmetry enhancement.
Posted by: QMW
Wed
8 May 2019
Duality invariant cosmology to all orders in alpha prime
Olaf Hohm
(Humboldt, Berlin)
Abstract:
I discuss the higher-derivative \alpha' corrections
in the reduction to one dimension (cosmic time)
that is relevant for the dynamics of cosmological backgrounds.
In this setting string theory is known to be duality invariant
under O(d,d), which makes it possible to completely classify all
\alpha' corrections. I discuss some generic features of the
\alpha' completed Friedmann equations and show that there are
duality invariant theories that allow for de Sitter solutions
that are non-perturbative in \alpha', suggesting that string theory
may permit de Sitter vacua in this novel fashion.
I discuss the higher-derivative \alpha' corrections
in the reduction to one dimension (cosmic time)
that is relevant for the dynamics of cosmological backgrounds.
In this setting string theory is known to be duality invariant
under O(d,d), which makes it possible to completely classify all
\alpha' corrections. I discuss some generic features of the
\alpha' completed Friedmann equations and show that there are
duality invariant theories that allow for de Sitter solutions
that are non-perturbative in \alpha', suggesting that string theory
may permit de Sitter vacua in this novel fashion.
Posted by: IC
Wed
1 May 2019
TBA
Wout Merbis
(ULB)
April 2019
Thu
25 Apr 2019
Boundary renormalisation group interfaces
Anatoly Konechny
(Heriot-Watt University)
Abstract:
Renormalisation group (RG) interfaces were introduced by I. Brunner and D. Roggenkamp in 2007. To construct such an interface consider perturbing a UV fixed point, described by a conformal field theory (CFT), by a relevant operator on a half space. Renormalising and letting the resulting QFT flow along the RG flow we obtain a conformal interface between the UV and IR fixed point CFTs. Although enjoying a full conformal symmetry this interface carries information about the RG flow it originated from.
In this talk I will consider a rather special case of the RG interface between two boundary conditions of a 2D CFT which is obtained from a boundary RG flow interpolating between two conformal boundary conditions. This interface is zero-dimensional and is thus described by a local boundary-condition changing operator. I investigate its properties in concrete models and formulate a number of general conjectures that can help charting phase diagrams of boundary RG flows.
Renormalisation group (RG) interfaces were introduced by I. Brunner and D. Roggenkamp in 2007. To construct such an interface consider perturbing a UV fixed point, described by a conformal field theory (CFT), by a relevant operator on a half space. Renormalising and letting the resulting QFT flow along the RG flow we obtain a conformal interface between the UV and IR fixed point CFTs. Although enjoying a full conformal symmetry this interface carries information about the RG flow it originated from.
In this talk I will consider a rather special case of the RG interface between two boundary conditions of a 2D CFT which is obtained from a boundary RG flow interpolating between two conformal boundary conditions. This interface is zero-dimensional and is thus described by a local boundary-condition changing operator. I investigate its properties in concrete models and formulate a number of general conjectures that can help charting phase diagrams of boundary RG flows.
Posted by: QMW
Thu
11 Apr 2019
Supersymmetric space-dependent deformations of ABJM
Matthew Roberts
(Imperial)
Abstract:
We construct new supersymmetric solutions of 11D supergravity, preserving 1/4 of the supersymmetry, that are dual to the ABJM Chern-Simons-matter theory deformed by mass terms which depend on one spatial direction. The BPS equations boil down to solving the Helmholtz equation on the complex plane giving rise to rich classes of new solutions. In particular, the construction gives rise to infinite classes of new supersymmetric รขโฌลboomerangรขโฌย RG flows, as well as generalising other previously known solutions.
We construct new supersymmetric solutions of 11D supergravity, preserving 1/4 of the supersymmetry, that are dual to the ABJM Chern-Simons-matter theory deformed by mass terms which depend on one spatial direction. The BPS equations boil down to solving the Helmholtz equation on the complex plane giving rise to rich classes of new solutions. In particular, the construction gives rise to infinite classes of new supersymmetric รขโฌลboomerangรขโฌย RG flows, as well as generalising other previously known solutions.
Posted by: QMW
Wed
10 Apr 2019
Black holes in N=4 Super-Yang-Mills
๐ London
Francesco Benini
(SISSA, Trieste)
Abstract:
AdS/CFT provides a consistent non-perturbative definition of quantum
gravity in asymptotically AdS space. Black holes should correspond to
ensembles of states in the boundary field theory. By analyzing the
superconformal index of 4d N=4 SU(N) Super-Yang-Mills, with the help
of a new Bethe Ansatz type formula, we are able to exactly reproduce
the Bekenstein-Hawking entropy of BPS black holes in AdS5 x S5. The
large N limit exhibits many competing contributions and Stokes
phenomena, hinting at new physics.
AdS/CFT provides a consistent non-perturbative definition of quantum
gravity in asymptotically AdS space. Black holes should correspond to
ensembles of states in the boundary field theory. By analyzing the
superconformal index of 4d N=4 SU(N) Super-Yang-Mills, with the help
of a new Bethe Ansatz type formula, we are able to exactly reproduce
the Bekenstein-Hawking entropy of BPS black holes in AdS5 x S5. The
large N limit exhibits many competing contributions and Stokes
phenomena, hinting at new physics.
Posted by: KCL
Wed
10 Apr 2019
Looking for Partially-Massless Gravity
Karapet Mkrtchyan
(Potsdam)
Abstract:
We study the possibility for a unitary theory of partially-massless (PM) spin-two field interacting with Gravity in arbitrary dimensions.
We show that parity invariant interactions respecting general covariance lead to a reconstruction of Conformal Gravity in even dimensions. In
this case the unitarity is sacrificed.
By relaxing the parity invariance, we find a possibility of a unitary theory in four dimensions, but the parity-odd cubic vertex cannot be written
in usual metric variables. We comment on possible approaches that may allow for the formulation of this theory.
Finally, by relaxing the general covariance, we show that a non-minimal coupling between massless and PM spin-two fields may lead to an
alternative possibility of a unitary theory, that necessarily involves mixed-symmetry fields.
We study the possibility for a unitary theory of partially-massless (PM) spin-two field interacting with Gravity in arbitrary dimensions.
We show that parity invariant interactions respecting general covariance lead to a reconstruction of Conformal Gravity in even dimensions. In
this case the unitarity is sacrificed.
By relaxing the parity invariance, we find a possibility of a unitary theory in four dimensions, but the parity-odd cubic vertex cannot be written
in usual metric variables. We comment on possible approaches that may allow for the formulation of this theory.
Finally, by relaxing the general covariance, we show that a non-minimal coupling between massless and PM spin-two fields may lead to an
alternative possibility of a unitary theory, that necessarily involves mixed-symmetry fields.
Posted by: IC
Tue
2 Apr 2019
TBA
Andreas Albrecht
(UC Davis)
Tue
2 Apr 2019
Tensionless Strings and Quantum Gravity Conjectures
Seung-Joo Lee
(CERN)
Abstract:
We test various conjectures on quantum gravity with general 6d string compactifications in the framework of F-theory. Starting with a gauge theory coupled to gravity, we first analyze the limit in Kรยคhler moduli space where the gauge coupling tends to zero while gravity is kept dynamical. A key observation is made about the appearance of a tensionless string in such a limit. For a more quantitative analysis, we focus on a U(1) gauge symmetry and determine the elliptic genus of this string in terms of certain meromorphic weak Jacobi forms, of which modular properties allow us to determine the charge-to-mass ratios of certain string excitations. A tower of these asymptotically massless charged states are then confirmed to satisfy the (sub-)Lattice Weak Gravity Conjecture, the Completeness Conjecture, and the Swampland Distance Conjecture. We interpret their charge-to-mass ratios in two a priori independent perspectives. All of this is then generalized to theories with multiple U(1)s. If time permits, we will also briefly report on our more recent 4-dimensional story.
We test various conjectures on quantum gravity with general 6d string compactifications in the framework of F-theory. Starting with a gauge theory coupled to gravity, we first analyze the limit in Kรยคhler moduli space where the gauge coupling tends to zero while gravity is kept dynamical. A key observation is made about the appearance of a tensionless string in such a limit. For a more quantitative analysis, we focus on a U(1) gauge symmetry and determine the elliptic genus of this string in terms of certain meromorphic weak Jacobi forms, of which modular properties allow us to determine the charge-to-mass ratios of certain string excitations. A tower of these asymptotically massless charged states are then confirmed to satisfy the (sub-)Lattice Weak Gravity Conjecture, the Completeness Conjecture, and the Swampland Distance Conjecture. We interpret their charge-to-mass ratios in two a priori independent perspectives. All of this is then generalized to theories with multiple U(1)s. If time permits, we will also briefly report on our more recent 4-dimensional story.
Posted by: CityU2
March 2019
Thu
28 Mar 2019
Partial deconfinement and holographic black holes
David Berenstein
(UC Santa Barbara)
Abstract:
I will describe simple models of holography that can display some of the thermodynamics associated to small black holes. These phenomena include negative specific heat and localization on additional dimensions of the geometry. I will also explain how the dynamics of these states should naturally be thought of as partial deconfinement on a submatrix set of degrees of freedom of the model.
I will describe simple models of holography that can display some of the thermodynamics associated to small black holes. These phenomena include negative specific heat and localization on additional dimensions of the geometry. I will also explain how the dynamics of these states should naturally be thought of as partial deconfinement on a submatrix set of degrees of freedom of the model.
Posted by: QMW
Wed
27 Mar 2019
Bootstrapping Inflationary Fluctuations
๐ London
Guilherme Leite Pimentel
(University of Amsterdam)
Abstract:
In flat space, four point scattering amplitudes at weak coupling can be fully determined from Lorentz symmetry, unitarity and causality. The resulting scattering amplitude depends on model details only through coupling constants and the particle content of the theory. I will show how the analogous story works in the case of inflationary fluctuations. We found explicit expressions for inflationary three and four-point functions, whose shapes depend on the field content of the theory, and do not depend on the specific inflationary model, as long as the fluctuations minimally break de Sitter symmetry. This ``cosmological bootstrapรขโฌย is a first step towards classifying all possible shapes of primordial non-gaussianity, which can be searched for in experimental data.
In flat space, four point scattering amplitudes at weak coupling can be fully determined from Lorentz symmetry, unitarity and causality. The resulting scattering amplitude depends on model details only through coupling constants and the particle content of the theory. I will show how the analogous story works in the case of inflationary fluctuations. We found explicit expressions for inflationary three and four-point functions, whose shapes depend on the field content of the theory, and do not depend on the specific inflationary model, as long as the fluctuations minimally break de Sitter symmetry. This ``cosmological bootstrapรขโฌย is a first step towards classifying all possible shapes of primordial non-gaussianity, which can be searched for in experimental data.
Posted by: KCL
Wed
27 Mar 2019
Infrared enhancement of supersymmetry in four dimensions
Simone Giacomelli
(Oxford)
Abstract:
In this seminar I will discuss a recently-found class of RG flows in four dimensions exhibiting enhancement of supersymmetry in the infrared, which provides a lagrangian description of several strongly-coupled N=2 SCFTs. The procedure involves starting from a N=2 SCFT, coupling a chiral multiplet in the adjoint representation of the global symmetry to the moment map of the SCFT and turning on a nilpotent expectation value for this chiral. We show that, combining considerations based on 't Hooft anomaly matching and basic results about the N=2 superconformal algebra, it is possible to understand in detail the mechanism underlying this phenomenon and formulate a simple criterion for supersymmetry enhancement.
In this seminar I will discuss a recently-found class of RG flows in four dimensions exhibiting enhancement of supersymmetry in the infrared, which provides a lagrangian description of several strongly-coupled N=2 SCFTs. The procedure involves starting from a N=2 SCFT, coupling a chiral multiplet in the adjoint representation of the global symmetry to the moment map of the SCFT and turning on a nilpotent expectation value for this chiral. We show that, combining considerations based on 't Hooft anomaly matching and basic results about the N=2 superconformal algebra, it is possible to understand in detail the mechanism underlying this phenomenon and formulate a simple criterion for supersymmetry enhancement.
Posted by: IC
Tue
26 Mar 2019
TBA
Sergej Moroz
(TU Munich)
Mon
25 Mar 2019
TBA
Sat Gupta
(UNC)
Thu
21 Mar 2019
From Soft Corrections to Ultra-Planckian Scattering and back
Massimo Bianchi
(Roma Tor Vergata)
Abstract:
Ultra-planckian collisions represent a fertile arena where to test quantum theories of gravity such as string theory. Glimpses of black hole formation and evaporation can be taken. For suitably defined infrared-safe observables, we show that the `classicalization' approach to high-multiplicity processes agrees with the ACV approach based on the resummation of ladder diagrams. Since a significant fraction of energy is lost in gravitational bremsstrahlung, we re-derived the zero-frequency limit (ZFL) of the GW flux using soft graviton theorems at leading order and compute the corrections at sub- and sub-sub-leading order. For massless two-particle elastic collisions the former is shown to vanish, while the latter takes an explicit expression which is checked against a simple tree-level process.However, if the tree-level form of the soft theorems is used at sub-sub-leading order even when the elastic amplitude needs resummation, an unphysical IR singularity occurs due to the infinite Coulomb phase. We briefly discuss a recent proposal as how to deal with these divergences and find agreement with the eikonal approach.
Ultra-planckian collisions represent a fertile arena where to test quantum theories of gravity such as string theory. Glimpses of black hole formation and evaporation can be taken. For suitably defined infrared-safe observables, we show that the `classicalization' approach to high-multiplicity processes agrees with the ACV approach based on the resummation of ladder diagrams. Since a significant fraction of energy is lost in gravitational bremsstrahlung, we re-derived the zero-frequency limit (ZFL) of the GW flux using soft graviton theorems at leading order and compute the corrections at sub- and sub-sub-leading order. For massless two-particle elastic collisions the former is shown to vanish, while the latter takes an explicit expression which is checked against a simple tree-level process.However, if the tree-level form of the soft theorems is used at sub-sub-leading order even when the elastic amplitude needs resummation, an unphysical IR singularity occurs due to the infinite Coulomb phase. We briefly discuss a recent proposal as how to deal with these divergences and find agreement with the eikonal approach.
Posted by: QMW
Wed
20 Mar 2019
3d Abelian Gauge theories at the Boundary
๐ London
Edoardo Lauria
(University of Durham)
Abstract:
A four-dimensional abelian gauge theory can be coupled to a 3d CFT with a U(1) symmetry living on a boundary. This coupling gives rise to a continuous family of boundary conformal field theories (BCFTs) parametrized by the gauge coupling \tau and by the choice of the CFT in the decoupling limit. Upon performing an Electric-Magnetic duality in the bulk and going to the decoupling limit in the new frame, one finds a different 3d CFT on the boundary, related to the original one by Witten's SL(2, Z) action. In particular the cusps on the real \tau axis correspond to the 3d gauging of the original CFT. We study general properties of this family of BCFTs. We show how to express bulk one and two-point functions, and the hemisphere free-energy, in terms of the two-point functions of the boundary electric and magnetic currents. Finally, upon assuming particle-vortex duality (and its fermionic version), we show how to turn this machinery into a powerful computational tool to study 3d gauge theories.
A four-dimensional abelian gauge theory can be coupled to a 3d CFT with a U(1) symmetry living on a boundary. This coupling gives rise to a continuous family of boundary conformal field theories (BCFTs) parametrized by the gauge coupling \tau and by the choice of the CFT in the decoupling limit. Upon performing an Electric-Magnetic duality in the bulk and going to the decoupling limit in the new frame, one finds a different 3d CFT on the boundary, related to the original one by Witten's SL(2, Z) action. In particular the cusps on the real \tau axis correspond to the 3d gauging of the original CFT. We study general properties of this family of BCFTs. We show how to express bulk one and two-point functions, and the hemisphere free-energy, in terms of the two-point functions of the boundary electric and magnetic currents. Finally, upon assuming particle-vortex duality (and its fermionic version), we show how to turn this machinery into a powerful computational tool to study 3d gauge theories.
Posted by: KCL
Wed
20 Mar 2019
Scattering amplitudes and their applications
Congkao Wen
(QMUL)
Abstract:
Scattering amplitudes are one of most important class of physical observables in quantum field theories. Over the last decade or so, there has been a lot of activities regarding the computation of scattering amplitudes in a wide range of interesting theories, where extremely powerful new frameworks for studying scattering amplitudes have emerged, known as the modern S-matrix program. In this talk I will review some of these powerful techniques, and discuss their applications. The applications will mostly focus on effective field theories, that include twistor-like formulas for scattering amplitudes of world-volume theories of probe D-brane and M5 brane, amplitude constraints on effective field theories, such as supersymmetric non-renormalization theorems, unitarity bounds on low-energy spectra.
Scattering amplitudes are one of most important class of physical observables in quantum field theories. Over the last decade or so, there has been a lot of activities regarding the computation of scattering amplitudes in a wide range of interesting theories, where extremely powerful new frameworks for studying scattering amplitudes have emerged, known as the modern S-matrix program. In this talk I will review some of these powerful techniques, and discuss their applications. The applications will mostly focus on effective field theories, that include twistor-like formulas for scattering amplitudes of world-volume theories of probe D-brane and M5 brane, amplitude constraints on effective field theories, such as supersymmetric non-renormalization theorems, unitarity bounds on low-energy spectra.
Posted by: CityU2
Tue
19 Mar 2019
TBA
Andres Collinucci
(ULB)
Tue
19 Mar 2019
TBA
Misha Portnoi
(Exeter)
Mon
18 Mar 2019
Moduli spaces of 4-dimensional N=3 superconformal field theories
Philip Argyres
(University of Cincinnati)
Fri
15 Mar 2019
Integrability, Poisson-Lie Symmetry and Double Field Theory
Hassler Falk
(University of Oviedo)
Abstract:
I review how integrability allows us to explore the planar limit of the AdS/CFT correspondence for arbitrary values of the t'Hooft coupling. In string theory integrability of the 2D รฦ-model is closely related to Poisson-Lie Symmetry. Double Field Theory can be used to make this symmetry manifest and therewith provides a new tool to study the implications for the gravity side of the correspondence.
I review how integrability allows us to explore the planar limit of the AdS/CFT correspondence for arbitrary values of the t'Hooft coupling. In string theory integrability of the 2D รฦ-model is closely related to Poisson-Lie Symmetry. Double Field Theory can be used to make this symmetry manifest and therewith provides a new tool to study the implications for the gravity side of the correspondence.
Posted by: IC
Wed
13 Mar 2019
Anomalous supersymmetry
๐ London
Marika Taylor
(University of Southampton)
Abstract:
We show that supersymmetry is anomalous in N = 1 superconformal quantum field theories (SCFTs) with an anomalous R-symmetry. This anomaly was originally found in holographic theories: here we show that this anomaly is present in general and demonstrate it for the massless superconformal Wess-Zumino model via a one loop computation of four-point functions of two supercurrents with either R-currents. In fact, the Wess-Zumino consistency conditions together with the standard R-symmetry anomaly imply the existence of the anomaly. We outline the implications of this anomaly.
We show that supersymmetry is anomalous in N = 1 superconformal quantum field theories (SCFTs) with an anomalous R-symmetry. This anomaly was originally found in holographic theories: here we show that this anomaly is present in general and demonstrate it for the massless superconformal Wess-Zumino model via a one loop computation of four-point functions of two supercurrents with either R-currents. In fact, the Wess-Zumino consistency conditions together with the standard R-symmetry anomaly imply the existence of the anomaly. We outline the implications of this anomaly.
Posted by: KCL
Wed
13 Mar 2019
Holographic Complexity in Vaidya Spacetimes
Shira Chapman
(University of Amsterdam)
Abstract:
We investigate holographic complexity for eternal black hole backgrounds perturbed by shock waves, with both the complexity=action (CA) and complexity=volume (CV) proposals. We consider Vaidya geometries describing a thin shell of null fluid with arbitrary energy falling in from one of the boundaries of a two-sided AdS-Schwarzschild spacetime. We demonstrate how scrambling and chaos are imprinted in the complexity of formation and in the full time evolution of complexity via the switchback effect for light shocks, as well as analogous properties for heavy ones.
We investigate holographic complexity for eternal black hole backgrounds perturbed by shock waves, with both the complexity=action (CA) and complexity=volume (CV) proposals. We consider Vaidya geometries describing a thin shell of null fluid with arbitrary energy falling in from one of the boundaries of a two-sided AdS-Schwarzschild spacetime. We demonstrate how scrambling and chaos are imprinted in the complexity of formation and in the full time evolution of complexity via the switchback effect for light shocks, as well as analogous properties for heavy ones.
Posted by: IC
Tue
12 Mar 2019
TBA
Costas Bachas
(ENS Paris)
Tue
12 Mar 2019
TBA
Ali Mostafazadeh
(Koc)
Thu
7 Mar 2019
The Cosmological Constant and the Electroweak Scale
๐ London
Henry Tye
Abstract:
KCL TPPC Seminar
KCL TPPC Seminar
Posted by: KCLphysics
Wed
6 Mar 2019
tba
Natalia Pinzani Fokeeva
(KU Leuven)
Wed
6 Mar 2019
Schwinger-Keldysh effective field theories
Natalia Pinzani Fokeeva
(KU Leuven)
Abstract:
I will discuss novel effective field theories for hydrodynamics. After identifying the relevant low-energy degrees of freedom, I will show how the symmetries of the problem can be efficiently implemented using supersymmetry. Interestingly, a conserved entropy current naturally arises as a Noether current in superspace. If time permits, I will also show how to derive such effective actions from holography.
I will discuss novel effective field theories for hydrodynamics. After identifying the relevant low-energy degrees of freedom, I will show how the symmetries of the problem can be efficiently implemented using supersymmetry. Interestingly, a conserved entropy current naturally arises as a Noether current in superspace. If time permits, I will also show how to derive such effective actions from holography.
Posted by: IC
Wed
6 Mar 2019
When black holes collide: Probing the quantum state of black holes by the spectrum of emitted gravitational waves
๐ London
Ramy Brustein
(Ben-Gurion University (Israel))
Abstract:
KCL TPPC Seminar
Abstract: Black hole (BH) mergers can be viewed as cosmological รขโฌลscattering experimentsรขโฌย resulting in an excited BH, which then decays to its ground state by emitting gravitational waves (GW). I will present general arguments, based on fundamental physics principles, as to why we should expect additional quantum ringdown modes to those predicted by general relativity. Then, I will discuss the spectrum of the predicted ringdown modes, the resulting emitted GW and the prospects for their detection in LIGO/VIRGO.
KCL TPPC Seminar
Abstract: Black hole (BH) mergers can be viewed as cosmological รขโฌลscattering experimentsรขโฌย resulting in an excited BH, which then decays to its ground state by emitting gravitational waves (GW). I will present general arguments, based on fundamental physics principles, as to why we should expect additional quantum ringdown modes to those predicted by general relativity. Then, I will discuss the spectrum of the predicted ringdown modes, the resulting emitted GW and the prospects for their detection in LIGO/VIRGO.
Posted by: KCLphysics
Wed
6 Mar 2019
Soft Heisenberg Hair
Daniel Grumiller
(TU Wien)
Abstract:
Gravity theories naturally allow for edge states generated by non-trivial boundary-condition preserving diffeomorphisms. I present a specific set of boundary conditions inspired by near horizon physics, show that it leads to soft hair excitations of black hole solutions and discuss implications for black hole entropy.
Gravity theories naturally allow for edge states generated by non-trivial boundary-condition preserving diffeomorphisms. I present a specific set of boundary conditions inspired by near horizon physics, show that it leads to soft hair excitations of black hole solutions and discuss implications for black hole entropy.
Posted by: IC
Tue
5 Mar 2019
Rationalizing CFTs
Matthew Buican
(QMUL)
Abstract:
2D rational conformal field theories (RCFTs) are typically thought of as being the รขโฌลnicestรขโฌย interesting CFTs we can study: They have large enough symmetry so that there are only a finite number of primary fields, but they also have applications to the real world (e.g., to various condensed matter systems). In this talk, I will describe a program that aims to understand connections between exotic 4D theories with N=2 superconformal symmetry and more down-to-earth 2D RCFTs, thereby enriching our understanding of both.
2D rational conformal field theories (RCFTs) are typically thought of as being the รขโฌลnicestรขโฌย interesting CFTs we can study: They have large enough symmetry so that there are only a finite number of primary fields, but they also have applications to the real world (e.g., to various condensed matter systems). In this talk, I will describe a program that aims to understand connections between exotic 4D theories with N=2 superconformal symmetry and more down-to-earth 2D RCFTs, thereby enriching our understanding of both.
Posted by: IC
Tue
5 Mar 2019
TBA
Weini Huang
(QMUL)
February 2019
Thu
28 Feb 2019
Asymptotic charges in gravity
Mahdi Godazgar
(QMUL)
Abstract:
I will give an overview of my recent research on the definition of asymptotic charges in asymptotically flat spacetimes, including the definition of subleading BMS charges and the relation to the conserved Newman-Penrose charges at null infinity.
I will give an overview of my recent research on the definition of asymptotic charges in asymptotically flat spacetimes, including the definition of subleading BMS charges and the relation to the conserved Newman-Penrose charges at null infinity.
Posted by: QMW
Wed
27 Feb 2019
Massive AdS Gravity from String Theory
๐ London
Costas Bachas
(Ecole Normale Superieure)
Abstract:
TBA
TBA
Posted by: KCL
Fri
22 Feb 2019
Hecke relations and Galois symmetries in Rational Conformal Field Theories and Modular Tensor Categories
Jeff Harvey
(The University of Chicago)
Abstract:
I will discuss some old and new relations between the characters, modular data and braiding and fusing matrices of rational conformal field theories and their
associated modular tensor categories. These relations involve concepts from number theory which I will explain in the talk.
I will discuss some old and new relations between the characters, modular data and braiding and fusing matrices of rational conformal field theories and their
associated modular tensor categories. These relations involve concepts from number theory which I will explain in the talk.
Posted by: QMW
Thu
21 Feb 2019
L_infinity algebras, the BV formalism, and Classical Fields
๐ London
Martin Wolf
(Surrey)
Abstract:
I will first review the Batalin-Vilkovisky formalism and its mathematical foundations with an emphasis on higher algebraic structures and classical field theories. I will then move on and discuss recent developments in formulating higher gauge theory with Lie quasi-groupoids as gauge structure. Finally, I will explain how all these ideas can be combined with those of twistor theory to formulate maximally superconformal gauge theories in four and six dimensions by means of quasi-isomorphisms.
I will first review the Batalin-Vilkovisky formalism and its mathematical foundations with an emphasis on higher algebraic structures and classical field theories. I will then move on and discuss recent developments in formulating higher gauge theory with Lie quasi-groupoids as gauge structure. Finally, I will explain how all these ideas can be combined with those of twistor theory to formulate maximally superconformal gauge theories in four and six dimensions by means of quasi-isomorphisms.
Posted by: KCL
Thu
21 Feb 2019
Twisting and localization in supergravity: equivariant cohomology of BPS black holes
๐ London
Imtak Jeon
(KCL)
Abstract:
I will talk about the formalism of supersymmetric localization in supergravity using the deformed BRST algebra defined in the presence of a supersymmetric background. The gravitational functional integral localizes onto the cohomology of a global supercharge
Q<sub>eq</sub>, obeying
(Q<sub>eq</sub>)<sup>2</sup>=H, where
H is a global symmetry of the background. This construction naturally produces a twisted version of supergravity whenever supersymmetry can be realized off-shell. I will present the details of the twisted graviton multiplet and ghost fields for the superconformal formulation of four-dimensional N=2 supergravity. As an application of our formalism, we systematize the computation of the exact quantum entropy of supersymmetric black holes. In particular, we compute the one-loop determinant of the Qeq deformation operator for the off-shell fluctuations of the Weyl multiplet around the
AdS<sub>2</sub>รโS<sup>2</sup> saddle.
I will talk about the formalism of supersymmetric localization in supergravity using the deformed BRST algebra defined in the presence of a supersymmetric background. The gravitational functional integral localizes onto the cohomology of a global supercharge
Q<sub>eq</sub>, obeying
(Q<sub>eq</sub>)<sup>2</sup>=H, where
H is a global symmetry of the background. This construction naturally produces a twisted version of supergravity whenever supersymmetry can be realized off-shell. I will present the details of the twisted graviton multiplet and ghost fields for the superconformal formulation of four-dimensional N=2 supergravity. As an application of our formalism, we systematize the computation of the exact quantum entropy of supersymmetric black holes. In particular, we compute the one-loop determinant of the Qeq deformation operator for the off-shell fluctuations of the Weyl multiplet around the
AdS<sub>2</sub>รโS<sup>2</sup> saddle.
Posted by: KCL
Thu
21 Feb 2019
3d Abelian Gauge theories at the Boundary
๐ London
Edoardo Lauria
(Durham)
Abstract:
A four-dimensional abelian gauge theory can be coupled to a 3d CFT with a U(1) symmetry living on a boundary. This coupling gives rise to a continuous family of boundary conformal field theories (BCFTs) parametrized by the gauge coupling รโ and by the choice of the CFT in the decoupling limit. Upon performing an Electric-Magnetic duality in the bulk and going to the decoupling limit in the new frame, one finds a different 3d CFT on the boundary, related to the original one by Witten's SL(2, Z) action. In particular the cusps on the real รโ axis correspond to the 3d gauging of the original CFT. We study general properties of this family of BCFTs. We show how to express bulk one and two-point functions, and the hemisphere free-energy, in terms of the two-point functions of the boundary electric and magnetic currents. Finally, upon assuming particle-vortex duality (and its fermionic version), we show how to turn this machinery into a powerful computational tool to study 3d gauge theories.
A four-dimensional abelian gauge theory can be coupled to a 3d CFT with a U(1) symmetry living on a boundary. This coupling gives rise to a continuous family of boundary conformal field theories (BCFTs) parametrized by the gauge coupling รโ and by the choice of the CFT in the decoupling limit. Upon performing an Electric-Magnetic duality in the bulk and going to the decoupling limit in the new frame, one finds a different 3d CFT on the boundary, related to the original one by Witten's SL(2, Z) action. In particular the cusps on the real รโ axis correspond to the 3d gauging of the original CFT. We study general properties of this family of BCFTs. We show how to express bulk one and two-point functions, and the hemisphere free-energy, in terms of the two-point functions of the boundary electric and magnetic currents. Finally, upon assuming particle-vortex duality (and its fermionic version), we show how to turn this machinery into a powerful computational tool to study 3d gauge theories.
Posted by: KCL
Thu
21 Feb 2019
Reflection and transmission coefficients for conformal interfaces.
Marco Meineri
(EPFL, Lausanne)
Abstract:
We probe a generic two dimensional conformal interface via a collider experiment. We measure the energy and charges which are reflected and transmitted through the interface. We find that the average transmitted energy is independent of the way the state is
constructed and determined by the central charge and a single piece of CFT data. We comment on the universality of the result and discuss some examples.
We probe a generic two dimensional conformal interface via a collider experiment. We measure the energy and charges which are reflected and transmitted through the interface. We find that the average transmitted energy is independent of the way the state is
constructed and determined by the central charge and a single piece of CFT data. We comment on the universality of the result and discuss some examples.
Posted by: QMW
Thu
21 Feb 2019
Entanglement Content of Quantum Particle Excitations
๐ London
Cecilia De Fazio
(City)
Abstract:
In the รฏยฌยrst part of my talk I will give a brief introduction to the main features of the Entaglement Entropy of a bipartite system in Integrable Quantum Field Theories and Conformal Field Theories. Secondly I will discuss the results my collaborators and I obtained in our two papers. In particular, I will consider the Entaglement Entropy of a single connected region of a รฏยฌยnite bipartite system in excited states described by one-dimensional massive free theories with รฏยฌยnite numbers of particles. I will show that in the limit of large volume and large length of the region the excess of entanglement due to the presence of the particles with respect to the ground state takes a simple form and admits a "q-bit interpretation".
In the รฏยฌยrst part of my talk I will give a brief introduction to the main features of the Entaglement Entropy of a bipartite system in Integrable Quantum Field Theories and Conformal Field Theories. Secondly I will discuss the results my collaborators and I obtained in our two papers. In particular, I will consider the Entaglement Entropy of a single connected region of a รฏยฌยnite bipartite system in excited states described by one-dimensional massive free theories with รฏยฌยnite numbers of particles. I will show that in the limit of large volume and large length of the region the excess of entanglement due to the presence of the particles with respect to the ground state takes a simple form and admits a "q-bit interpretation".
Posted by: KCL
Thu
21 Feb 2019
Thermo/HydroDynamics of the classical Toda system and random matrix theory
๐ London
Benjamin Doyon
(KCL)
Abstract:
This will be presenting mainly some of my recent work, and also aspects of recent work of Herbert Spohn, both developed in parallel. The classical Toda system is a one-dimensional integrable many-body system, which can be seen either as a gas of particles or as a chain of degrees of freedom. Herbert has shown how the generalised Gibbs ensembles of the Toda chain can be obtained from a certain limit of the beta-ensemble in random matrix theory. Analysing and connecting the gas and chain viewpoints, I have obtained both the generalised Gibbs ensembles and generalised hydrodynamics from a quasiparticle scattering description. Thus we make a connection between quasiparticle scattering and random matrix theory.
This will be presenting mainly some of my recent work, and also aspects of recent work of Herbert Spohn, both developed in parallel. The classical Toda system is a one-dimensional integrable many-body system, which can be seen either as a gas of particles or as a chain of degrees of freedom. Herbert has shown how the generalised Gibbs ensembles of the Toda chain can be obtained from a certain limit of the beta-ensemble in random matrix theory. Analysing and connecting the gas and chain viewpoints, I have obtained both the generalised Gibbs ensembles and generalised hydrodynamics from a quasiparticle scattering description. Thus we make a connection between quasiparticle scattering and random matrix theory.
Posted by: KCL
Wed
20 Feb 2019
Witten, Cardy, and the Holonomy Saddle
๐ London
Piljin Yi
(KIAS)
Abstract:
This talk will explore topological invariants of susy
gauge theories, with some emphasis on index-like
quantities and the notion of holonomy saddles.
We start with 1d refined Witten index computations
where the twisted partition functions typically show
rational, rather than integral, behavior. We will explain
how this oddity is a blessing in disguise and propose
a universal tool for extracting the truely enumerative
Witten indices. In part, this finally put to the rest
a two-decade-old bound state problems which had
originated from the M-theory hypothesis.
Along the way, we resolve an old and critical conflict
between Kac+Smilga and Staudacher/Pestun, circa
1999~2002, whereby the notion of holonomy saddles
emerges and plays a crucial role. More importantly,
the holonomy saddle prove to be universal features
of supersymmetric gauge theories when the spacetime
include a small circle. We explore them further for
d=4, N=1 theories, with much ramifications on recent
claims on Cardy exponents of their partition functions.
This talk will explore topological invariants of susy
gauge theories, with some emphasis on index-like
quantities and the notion of holonomy saddles.
We start with 1d refined Witten index computations
where the twisted partition functions typically show
rational, rather than integral, behavior. We will explain
how this oddity is a blessing in disguise and propose
a universal tool for extracting the truely enumerative
Witten indices. In part, this finally put to the rest
a two-decade-old bound state problems which had
originated from the M-theory hypothesis.
Along the way, we resolve an old and critical conflict
between Kac+Smilga and Staudacher/Pestun, circa
1999~2002, whereby the notion of holonomy saddles
emerges and plays a crucial role. More importantly,
the holonomy saddle prove to be universal features
of supersymmetric gauge theories when the spacetime
include a small circle. We explore them further for
d=4, N=1 theories, with much ramifications on recent
claims on Cardy exponents of their partition functions.
Posted by: KCL
Tue
19 Feb 2019
New routes to scattering on curved backgrounds
Tim Adamo
(Imperial College)
Abstract:
There are many reasons to consider perturbative QFT around curved backgrounds, but it is often difficult to perform explicit computations in these settings. Progress in the study of scattering amplitudes (around a trivial background) suggests alternative perspectives to space-time Lagrangians and Feynman rules which could enable progress in the study of scattering on curved backgrounds. I will discuss one such alternative, known as double copy, with a particular focus on gluon and graviton scattering around non-linear plane wave backgrounds
There are many reasons to consider perturbative QFT around curved backgrounds, but it is often difficult to perform explicit computations in these settings. Progress in the study of scattering amplitudes (around a trivial background) suggests alternative perspectives to space-time Lagrangians and Feynman rules which could enable progress in the study of scattering on curved backgrounds. I will discuss one such alternative, known as double copy, with a particular focus on gluon and graviton scattering around non-linear plane wave backgrounds
Posted by: IC
Tue
19 Feb 2019
From Yang-Mills and Maxwell in de Sitter space electromagnetic knots
Olaf Lechtenfeld
(Hannover)
Abstract:
I will review analytic SU(2) Yang-Mills solutions with finite action on de Sitter space from a new perspective. As a byproduct, all abelian solutions are classified and related with rational electromagnetic knots. In the Yang-Mills case, the gravitational backreaction is easily taken in to account as well.
I will review analytic SU(2) Yang-Mills solutions with finite action on de Sitter space from a new perspective. As a byproduct, all abelian solutions are classified and related with rational electromagnetic knots. In the Yang-Mills case, the gravitational backreaction is easily taken in to account as well.
Posted by: CityU2
Thu
14 Feb 2019
How logarithms are born
Melissa van Beekveld
(IMAPP Njimegen)
Abstract:
I will show how large logarithms arise in a perturbative calculation and how resummation solves the issue of having these large logarithms. If there is some time left, I want to show some recent progress that we have made on pinning down the origin of the next-to-leading class of logarithms.
I will show how large logarithms arise in a perturbative calculation and how resummation solves the issue of having these large logarithms. If there is some time left, I want to show some recent progress that we have made on pinning down the origin of the next-to-leading class of logarithms.
Posted by: QMW
Wed
13 Feb 2019
String theory compactifications with sources
๐ London
Alessandro Tomasiello
(Universita di Milano-Bicocca)
Abstract:
In recent years, more and more compactifications have emerged whose existence depends crucially on the presence of internal sources to the supergravity fields, such as D-branes and orientifold planes. I will review some solutions of this type in various dimensions, and illustrate their applications to holography and potentially to the problem of finding de Sitter solutions.
In recent years, more and more compactifications have emerged whose existence depends crucially on the presence of internal sources to the supergravity fields, such as D-branes and orientifold planes. I will review some solutions of this type in various dimensions, and illustrate their applications to holography and potentially to the problem of finding de Sitter solutions.
Posted by: KCL
Wed
13 Feb 2019
Gauge theories phases of 5d SCFTs: an M-theory/type IIA perpective
Cyril Closset
Abstract:
I will revisit the well-known construction of 5d SCFTs from M-theory on a CY3 singularity. Upon massive deformation, such 5d SCFTs are often expected to have 5d N=1 supersymmetric gauge theory descriptions at low energy. I will present a new way to study these 5d ``gauge theory phases'' systematically using type-IIA string theory, and I will comment on the phenomenon of "UV duality." Along the way, I will discuss some slightly subtle properties of the 5d N=1 Coulomb branch prepotential.
I will revisit the well-known construction of 5d SCFTs from M-theory on a CY3 singularity. Upon massive deformation, such 5d SCFTs are often expected to have 5d N=1 supersymmetric gauge theory descriptions at low energy. I will present a new way to study these 5d ``gauge theory phases'' systematically using type-IIA string theory, and I will comment on the phenomenon of "UV duality." Along the way, I will discuss some slightly subtle properties of the 5d N=1 Coulomb branch prepotential.
Posted by: IC
Tue
12 Feb 2019
TBA
Radu Tatar
(Liverpool)
Wed
6 Feb 2019
TBA
Eliezer Rabinovici
(HUJ)
Wed
6 Feb 2019
A Worldsheet Dual for the Symmetric Orbifold
Rajesh Gopakumar
(ICTS-TIFR)
Abstract:
We will argue that superstring theory on \({\rm AdS}_3\times {\rm S}^3\times \mathbb{T}^4\) with the smallest amount of NS-NS flux (``\(k=1\)'') is dual to the spacetime CFT given by the large \(N\) limit of the free symmetric product orbifold \(\mathrm{Sym}^N(\mathbb{T}^4)\). The worldsheet theory, at \(k=1\), is defined using the hybrid formalism in which the \({\rm AdS}_3\times {\rm S}^3\) part is described by a \(\mathfrak{psu}(1,1|2)_1\) WZW model (which is well defined).
Unlike the case for \(k\geq 2\), it turns out that the string spectrum at \(k=1\) does not exhibit a long string continuum, and perfectly matches with the large \(N\) limit of the symmetric product. The fusion rules of the symmetric orbifold are also reproduced from the worldsheet perspective.
This proposal therefore affords a tractable worldsheet description of a tensionless limit in string theory.
We will argue that superstring theory on \({\rm AdS}_3\times {\rm S}^3\times \mathbb{T}^4\) with the smallest amount of NS-NS flux (``\(k=1\)'') is dual to the spacetime CFT given by the large \(N\) limit of the free symmetric product orbifold \(\mathrm{Sym}^N(\mathbb{T}^4)\). The worldsheet theory, at \(k=1\), is defined using the hybrid formalism in which the \({\rm AdS}_3\times {\rm S}^3\) part is described by a \(\mathfrak{psu}(1,1|2)_1\) WZW model (which is well defined).
Unlike the case for \(k\geq 2\), it turns out that the string spectrum at \(k=1\) does not exhibit a long string continuum, and perfectly matches with the large \(N\) limit of the symmetric product. The fusion rules of the symmetric orbifold are also reproduced from the worldsheet perspective.
This proposal therefore affords a tractable worldsheet description of a tensionless limit in string theory.
Posted by: CityU2
Tue
5 Feb 2019
Topologically Ordered Matter and Why You Should be Interested
Steven Simon
(Oxford)
Abstract:
In two dimensional topological phases of matter, processes
depend on gross topology rather than detailed geometry. Thinking in 2+1
dimensions, particle world lines can be interpreted as knots or links,
and the amplitude for certain processes becomes a topological invariant
of that link. While sounding rather exotic, we believe that such phases
of matter not only exist, but have actually been observed in quantum
Hall experiments, and could provide a uniquely practical route to
building a quantum computer. Possibilities have also been proposed for
creating similar physics in systems ranging from superfluid helium to
strontium ruthenate to semiconductor-superconductor junctions to quantum
wires to spin systems to graphene to cold atoms.
In two dimensional topological phases of matter, processes
depend on gross topology rather than detailed geometry. Thinking in 2+1
dimensions, particle world lines can be interpreted as knots or links,
and the amplitude for certain processes becomes a topological invariant
of that link. While sounding rather exotic, we believe that such phases
of matter not only exist, but have actually been observed in quantum
Hall experiments, and could provide a uniquely practical route to
building a quantum computer. Possibilities have also been proposed for
creating similar physics in systems ranging from superfluid helium to
strontium ruthenate to semiconductor-superconductor junctions to quantum
wires to spin systems to graphene to cold atoms.
Posted by: IC
Tue
5 Feb 2019
Mode interactions in complex and disordered patterns
Alastair Rucklidge
(Leeds)
Abstract:
Why do some systems organise themselves into well ordered patterns with astonishing symmetry and regularity, while other superficially similar systems produce defects and disorder? In systems where two different length scales are unstable, the nonlinear interaction between the different modes is key: steady complex patterns can be stabilised when the modes act together to reinforce each other. But, if the two types of pattern compete with each other, the outcome can be considerably more complicated: a time-dependent disordered mixture of patterns constantly shifting and changing. In a small domain, the nature of the interaction between a small number of modes on each length scale can readily be computed. In a large domain, each mode can interact with hundreds of other modes, but the overall behaviour still appears to be guided by small-domain considerations.
Why do some systems organise themselves into well ordered patterns with astonishing symmetry and regularity, while other superficially similar systems produce defects and disorder? In systems where two different length scales are unstable, the nonlinear interaction between the different modes is key: steady complex patterns can be stabilised when the modes act together to reinforce each other. But, if the two types of pattern compete with each other, the outcome can be considerably more complicated: a time-dependent disordered mixture of patterns constantly shifting and changing. In a small domain, the nature of the interaction between a small number of modes on each length scale can readily be computed. In a large domain, each mode can interact with hundreds of other modes, but the overall behaviour still appears to be guided by small-domain considerations.
Posted by: CityU2
Mon
4 Feb 2019
Single trace TTbar-deformations and AdS/CFT
๐ London
Gaston Giribet
(UBA)
Abstract:
A solvable irrelevant deformation of AdS3/CFT2 correspondence leading to a theory with Hagedorn spectrum at high energy has been recently proposed by Kutasov et al. It consists of a single trace deformation of the boundary theory, which is inspired by the recent work on solvable T\bar{T}-deformations of two-dimensional CFTs. Thought of as a worldsheet sigma-model, the interpretation of the deformed theory from the bulk viewpoint is that of string theory on a background that interpolates between AdS3 in the IR and a linear dilaton vacuum of little string theory in the UV. In this talk, after giving an introduction to this class of solvable theories, I will present explicit results for their observables.
A solvable irrelevant deformation of AdS3/CFT2 correspondence leading to a theory with Hagedorn spectrum at high energy has been recently proposed by Kutasov et al. It consists of a single trace deformation of the boundary theory, which is inspired by the recent work on solvable T\bar{T}-deformations of two-dimensional CFTs. Thought of as a worldsheet sigma-model, the interpretation of the deformed theory from the bulk viewpoint is that of string theory on a background that interpolates between AdS3 in the IR and a linear dilaton vacuum of little string theory in the UV. In this talk, after giving an introduction to this class of solvable theories, I will present explicit results for their observables.
Posted by: KCL
January 2019
Thu
31 Jan 2019
Field theory of gapped momentum states
Kostya Trachenko
(QMUL)
Abstract:
Understanding most basic thermodynamic properties of liquids such as energy and heat capacity turned out to be a long-standing problem in physics [1]. Landau&Lifshitz textbook states that no general formulas can be derived for liquid thermodynamic functions because the interactions are both strong and system-specific. Phrased differently, liquids have no small parameter. Recent results have opened a new way to understand liquid thermodynamics on the basis of collective modes (phonons) as is done in the solid state theory. There are important differences between phonons in solids and liquids, and we have recently started to understand and quantify this difference. One striking difference is the emergence of a gap in the liquid phonon spectrum in the reciprocal space [2]. This brings an interesting question of what kind of field theory describes this gap. We recently proposed a two-field Lagrangian which accounts for dissipation and predicts the gap in momentum space [3]. The dissipative and mass terms compete by promoting gaps in k-space and energy, respectively (when bare mass is close to the field hopping frequency, both gaps close and the dissipative term annihilates the bare mass.) I will also discuss the recent attempt to canonically quantize this theory where I attempted to describe quantum dissipation which has been of interest recently. The Hamiltonian is quantized in terms of particles and antiparticles as in the complex scalar field theory and has the energy spectrum with the gap in momentum space. Finally, I will discuss the emergence of ultraviolet and infrared cutoffs in this theory due to dissipation.
[1] K. Trachenko and V. V. Brazhkin, Collective modes and thermodynamics of the liquid state, Reports on Progress in Physics 79, 016502 (2016).
[2] C. Yang, M. T. Dove, V. V. Brazhkin and K. Trachenko, Physical Review Letters 118, 215502 (2017).
[3] K. Trachenko, Physical Review E 96, 062134 (2017).
Understanding most basic thermodynamic properties of liquids such as energy and heat capacity turned out to be a long-standing problem in physics [1]. Landau&Lifshitz textbook states that no general formulas can be derived for liquid thermodynamic functions because the interactions are both strong and system-specific. Phrased differently, liquids have no small parameter. Recent results have opened a new way to understand liquid thermodynamics on the basis of collective modes (phonons) as is done in the solid state theory. There are important differences between phonons in solids and liquids, and we have recently started to understand and quantify this difference. One striking difference is the emergence of a gap in the liquid phonon spectrum in the reciprocal space [2]. This brings an interesting question of what kind of field theory describes this gap. We recently proposed a two-field Lagrangian which accounts for dissipation and predicts the gap in momentum space [3]. The dissipative and mass terms compete by promoting gaps in k-space and energy, respectively (when bare mass is close to the field hopping frequency, both gaps close and the dissipative term annihilates the bare mass.) I will also discuss the recent attempt to canonically quantize this theory where I attempted to describe quantum dissipation which has been of interest recently. The Hamiltonian is quantized in terms of particles and antiparticles as in the complex scalar field theory and has the energy spectrum with the gap in momentum space. Finally, I will discuss the emergence of ultraviolet and infrared cutoffs in this theory due to dissipation.
[1] K. Trachenko and V. V. Brazhkin, Collective modes and thermodynamics of the liquid state, Reports on Progress in Physics 79, 016502 (2016).
[2] C. Yang, M. T. Dove, V. V. Brazhkin and K. Trachenko, Physical Review Letters 118, 215502 (2017).
[3] K. Trachenko, Physical Review E 96, 062134 (2017).
Posted by: QMW
Wed
30 Jan 2019
Cosmic censorship violation and black hole collisions in higher dimensions
๐ London
Roberto Emparan
(ICREA, Barcelona)
Abstract:
The cosmic censorship conjecture raises the question of whether classical gravitational dynamics can drive a low-energy configuration into an accessible regime of quantum gravity, with Planck-scale curvatures and energy densities visible by distant observers. I will present evidence that cosmic censorhip is violated in the quintessential phenomenon of General Relativity: the collision and merger of two black holes. It only requires a sufficient total angular momentum in a collision in high enough number of dimensions. Nevertheless, I will argue that even if cosmic censorship is violated in this and in some other know instances, its spirit remains unchallenged: classical relativity describes the physics seen by observers outside the black holes accurately, with only minimal quantum input that does not entail macroscopic disruptions.
The cosmic censorship conjecture raises the question of whether classical gravitational dynamics can drive a low-energy configuration into an accessible regime of quantum gravity, with Planck-scale curvatures and energy densities visible by distant observers. I will present evidence that cosmic censorhip is violated in the quintessential phenomenon of General Relativity: the collision and merger of two black holes. It only requires a sufficient total angular momentum in a collision in high enough number of dimensions. Nevertheless, I will argue that even if cosmic censorship is violated in this and in some other know instances, its spirit remains unchallenged: classical relativity describes the physics seen by observers outside the black holes accurately, with only minimal quantum input that does not entail macroscopic disruptions.
Posted by: KCL
Tue
29 Jan 2019
Q-operators for rational spin chains
Rouven Frassek
(MPIM Bonn)
Abstract:
I plan to discuss how Q-operators for rational spin chains can be constructed in the framework of the quantum inverse scattering method. The presentation will include open and closed XXX type spin chains with compact and non-compact representations of sl(2) in the quantum space. Further I plan to elaborate on the generalisation to spin chains of higher rank and in particular u(2,2|4) which underlies N=4 super Yang-Mills theory at weak coupling. Finally I will discuss the classification of the oscillator type solutions to the Yang-Baxter equation that are relevant to build Q-operators and give an outlook.
I plan to discuss how Q-operators for rational spin chains can be constructed in the framework of the quantum inverse scattering method. The presentation will include open and closed XXX type spin chains with compact and non-compact representations of sl(2) in the quantum space. Further I plan to elaborate on the generalisation to spin chains of higher rank and in particular u(2,2|4) which underlies N=4 super Yang-Mills theory at weak coupling. Finally I will discuss the classification of the oscillator type solutions to the Yang-Baxter equation that are relevant to build Q-operators and give an outlook.
Posted by: CityU2
Thu
24 Jan 2019
The Uses of Lattice Topological Defects
Paul Fendley
(Oxford)
Abstract:
I give an overview of work with Aasen and Mong on topological defects in two-dimensional classical lattice models, quantum spin chains and tensor networks. The partition function in the presence of a topological defect is invariant under any local deformation of the defect. By using results from fusion categories, we construct topological defects in a wide class of lattice models, and show how to use them to derive exact properties of field theories by explicit lattice calculations. In the Ising model, the fusion of duality defects allows Kramers-Wannier duality to be enacted on the torus and higher genus surfaces easily, implementing modular invariance directly on the lattice. In other models, the construction leads to generalised dualities previously unknown. A consequence is an explicit definition of twisted boundary conditions that yield the precise shift in momentum quantization and for critical theories, the spin of the associated conformal field. Other universal quantities we compute exactly on the lattice are the ratios of g-factors for conformal boundary conditions
I give an overview of work with Aasen and Mong on topological defects in two-dimensional classical lattice models, quantum spin chains and tensor networks. The partition function in the presence of a topological defect is invariant under any local deformation of the defect. By using results from fusion categories, we construct topological defects in a wide class of lattice models, and show how to use them to derive exact properties of field theories by explicit lattice calculations. In the Ising model, the fusion of duality defects allows Kramers-Wannier duality to be enacted on the torus and higher genus surfaces easily, implementing modular invariance directly on the lattice. In other models, the construction leads to generalised dualities previously unknown. A consequence is an explicit definition of twisted boundary conditions that yield the precise shift in momentum quantization and for critical theories, the spin of the associated conformal field. Other universal quantities we compute exactly on the lattice are the ratios of g-factors for conformal boundary conditions
Posted by: QMW
Wed
23 Jan 2019
What spatial geometry does the (2+1)-d QFT vacuum prefer?
๐ London
Toby Wiseman
(Imperial College London)
Abstract:
We consider the energy of a (2+1)-d relativistic QFT on a
deformation of flat space in either the quantum or thermal vacuum state.
Looking at both free scalars and fermions, with and without mass (and in
the scalar case including a curvature coupling) we surprisingly find
that any deformation of flat space is always energetically preferred to
flat space itself. This is a UV finite effect, insensitive to any cut-
off. We see the same behaviour for any (2+1)-holographic CFT which we
compute via the gravity dual. We consider the physical application of this to membranes carrying
relativistic degrees of freedom, the vacuum energy of which then induce
a tendency for the membrane to crumple. An interesting case is monolayer
graphene, which experimentally is observed to ripple, and on large
scales can be understood as a membrane carrying free massless Dirac degrees
of freedom.
We consider the energy of a (2+1)-d relativistic QFT on a
deformation of flat space in either the quantum or thermal vacuum state.
Looking at both free scalars and fermions, with and without mass (and in
the scalar case including a curvature coupling) we surprisingly find
that any deformation of flat space is always energetically preferred to
flat space itself. This is a UV finite effect, insensitive to any cut-
off. We see the same behaviour for any (2+1)-holographic CFT which we
compute via the gravity dual. We consider the physical application of this to membranes carrying
relativistic degrees of freedom, the vacuum energy of which then induce
a tendency for the membrane to crumple. An interesting case is monolayer
graphene, which experimentally is observed to ripple, and on large
scales can be understood as a membrane carrying free massless Dirac degrees
of freedom.
Posted by: KCL
Tue
22 Jan 2019
Graphene and Boundary Conformal Field Theory
Chris Herzog
(King's)
Abstract:
The infrared fixed point of graphene under the renormalization group flow is a relatively under studied yet important example of a boundary conformal field theory with a number of remarkable properties. It has a close relationship with three dimensional QED. It maps to itself under electric-magnetic duality. Moreover, it along with its supersymmetric cousins all possess an exactly marginal coupling – the charge of the electron – which allows for straightforward perturbative calculations in the weak coupling limit. I will review past work on this model and also discuss my own contributions, which focus on understanding the boundary contributions to the anomalous trace of the stress tensor and their role in helping to understand the structure of boundary conformal field theory.
The infrared fixed point of graphene under the renormalization group flow is a relatively under studied yet important example of a boundary conformal field theory with a number of remarkable properties. It has a close relationship with three dimensional QED. It maps to itself under electric-magnetic duality. Moreover, it along with its supersymmetric cousins all possess an exactly marginal coupling – the charge of the electron – which allows for straightforward perturbative calculations in the weak coupling limit. I will review past work on this model and also discuss my own contributions, which focus on understanding the boundary contributions to the anomalous trace of the stress tensor and their role in helping to understand the structure of boundary conformal field theory.
Posted by: CityU2
Thu
17 Jan 2019
4D scattering equations, Monte Carlo methods, and conformal supergravity
Joseph Farrow
(Durham U.)
Abstract:
I will introduce the framework of 4D scattering equations for calculating tree level super amplitudes in a variety of different theories, including Einstein supergravity and super Yang-Mills theory. I will discuss my work on numerical solutions to these equations by Monte Carlo methods, and work with Arthur Lipstein on calculating N=4 conformal supergravity amplitudes in this framework.
I will introduce the framework of 4D scattering equations for calculating tree level super amplitudes in a variety of different theories, including Einstein supergravity and super Yang-Mills theory. I will discuss my work on numerical solutions to these equations by Monte Carlo methods, and work with Arthur Lipstein on calculating N=4 conformal supergravity amplitudes in this framework.
Posted by: QMW
Wed
9 Jan 2019
General lessons on 4d SCFTs from Geometry
Mario Martone
(UT Austin)
Abstract:
The geometry of the moduli space of 4d \mathcal{N}=2 moduli spaces, and in particular of their Coulomb branches (CBs), is very constrained. In this talk I will show that through its careful study, we can learn general and somewhat surprising lessons about the properties of \mathcal{N}=2 super conformal field theories (SCFTs). Specifically I will show that we can prove that the scaling dimension of CB coordinates, and thus of the corresponding operator at the SCFT fixed point, has to be rational and it has a rank-dependent maximum value and that in general the moduli spaces of \mathcal{N}=2 SCFTs can have metric singularities as well as complex structure singularities.
Finally I will outline how we can explicitly perform a classification of geometries of \mathcal{N}\geq3 SCFTs and carry out the program up to rank-2. The results are surprising and exciting in many ways.
The geometry of the moduli space of 4d \mathcal{N}=2 moduli spaces, and in particular of their Coulomb branches (CBs), is very constrained. In this talk I will show that through its careful study, we can learn general and somewhat surprising lessons about the properties of \mathcal{N}=2 super conformal field theories (SCFTs). Specifically I will show that we can prove that the scaling dimension of CB coordinates, and thus of the corresponding operator at the SCFT fixed point, has to be rational and it has a rank-dependent maximum value and that in general the moduli spaces of \mathcal{N}=2 SCFTs can have metric singularities as well as complex structure singularities.
Finally I will outline how we can explicitly perform a classification of geometries of \mathcal{N}\geq3 SCFTs and carry out the program up to rank-2. The results are surprising and exciting in many ways.
Posted by: IC