Triangle Seminars
July 2022
Tue
12 Jul 2022
Emergent Cosmology From Matrix Theory
Samuel Laliberte
(McGill University)
Abstract:
Matrix theory is a proposed non-perturbative definition of superstring theory in which space is emergent. Recently, it was shown that a 4-dimensional expanding universe can emerge in the IKKT matrix model, with another 6 spatial dimensions stabilized at the string scale. This scenario was also explored in the BFSS model, in which case the emerging phase yields a scale-invariant spectrum of scalar and tensor perturbation. In this talk, we will discuss recent progress in understanding these results. More precisely, we will discuss a possible way of obtaining the metric out of the matrices in the IKKT model, and ways to probe symmetry breaking in the BFSS model.
Matrix theory is a proposed non-perturbative definition of superstring theory in which space is emergent. Recently, it was shown that a 4-dimensional expanding universe can emerge in the IKKT matrix model, with another 6 spatial dimensions stabilized at the string scale. This scenario was also explored in the BFSS model, in which case the emerging phase yields a scale-invariant spectrum of scalar and tensor perturbation. In this talk, we will discuss recent progress in understanding these results. More precisely, we will discuss a possible way of obtaining the metric out of the matrices in the IKKT model, and ways to probe symmetry breaking in the BFSS model.
Posted by: IC
Tue
5 Jul 2022
The Higgs/Amplitude Mode from Holography
Aristomenis Donos
(Durham university)
Abstract:
Second order thermal phase transitions are driven my an order parameter which comes with an amplitude. Fluctuations of this amplitude lead to a slowly decaying mode whose gap closes to zero at the critical point. I will use holographic techniques to discuss in detail how this gapped mode determines the linear response of scalar operators close to the phase transition and give a geometric expression for the dissipative coefficient that fixes the relevant Greenรขโฌโขs functions.
Second order thermal phase transitions are driven my an order parameter which comes with an amplitude. Fluctuations of this amplitude lead to a slowly decaying mode whose gap closes to zero at the critical point. I will use holographic techniques to discuss in detail how this gapped mode determines the linear response of scalar operators close to the phase transition and give a geometric expression for the dissipative coefficient that fixes the relevant Greenรขโฌโขs functions.
Posted by: IC
June 2022
Wed
29 Jun 2022
Analytic Q-systems and AdS3/CFT2 Quantum Spectral Curve
๐ London
Simon Ekhammar
Abstract:
The Quantum Spectral Curve (QSC) is a powerful integrability-based method capable of computing the spectrum of planar N=4 SYM. It has also been generalised in many directions, for example to cusped Wilson lines and various deformations. The success of the QSC motivates trying to extend the formalism beyond N=4 to other theories. This requires the study of the underlying structure of the QSC, a so called analytic Q-system. To construct an analytic Q-system it is necessary to specify both its algebraic structure, usually encoded into QQ-relations, and its analytic properties.
I will talk about recent work to study Q-systems beyond the ones relevant for N=4, discussing both their algebraic and analytic properties. In particular I will discuss the recent conjecture of a QSC for AdS3/CFT2 which non-trivially couples two different Q-systems. While the curve shares many features with the N=4 QSC it also offers new surprises and challenges. If this new curve can be brought under full control and further tested many interesting applications and generalisations are within reach.
The Quantum Spectral Curve (QSC) is a powerful integrability-based method capable of computing the spectrum of planar N=4 SYM. It has also been generalised in many directions, for example to cusped Wilson lines and various deformations. The success of the QSC motivates trying to extend the formalism beyond N=4 to other theories. This requires the study of the underlying structure of the QSC, a so called analytic Q-system. To construct an analytic Q-system it is necessary to specify both its algebraic structure, usually encoded into QQ-relations, and its analytic properties.
I will talk about recent work to study Q-systems beyond the ones relevant for N=4, discussing both their algebraic and analytic properties. In particular I will discuss the recent conjecture of a QSC for AdS3/CFT2 which non-trivially couples two different Q-systems. While the curve shares many features with the N=4 QSC it also offers new surprises and challenges. If this new curve can be brought under full control and further tested many interesting applications and generalisations are within reach.
Posted by: andrea
Tue
28 Jun 2022
Extended operators in CFTs, twists of 4d N=2 theories and extended VOAs.
Matteo Lotito
(University of Massachusetts Amherst)
Abstract:
In recent years, it has been understood how local operators do not paint the entire picture of a quantum field theory, but we need to introduce extended operators to understand finer details about these theories.
Motivated by this, we investigate a subset of these extended operators in particular in the context of 4d N=2 superconformal field theories.
I will start by introducing the setup that we use to describe the possible configurations of these extended operators.
I will also compare and contrast the operators that appear in our framework with the more familiar (Wilson and 't Hooft) line operators.
Time permitting, I will then introduce twists of these theories by a choice of an appropriate nilpotent supercharge. The restriction to (extended) operators living in the cohomology of this supercharge gives rise to interesting algebraic structures, that are analogous to, or rather an extension of, the 2d vertex operator algebras that have now become familiar familiar in the context of 4d N=2 theories.
In recent years, it has been understood how local operators do not paint the entire picture of a quantum field theory, but we need to introduce extended operators to understand finer details about these theories.
Motivated by this, we investigate a subset of these extended operators in particular in the context of 4d N=2 superconformal field theories.
I will start by introducing the setup that we use to describe the possible configurations of these extended operators.
I will also compare and contrast the operators that appear in our framework with the more familiar (Wilson and 't Hooft) line operators.
Time permitting, I will then introduce twists of these theories by a choice of an appropriate nilpotent supercharge. The restriction to (extended) operators living in the cohomology of this supercharge gives rise to interesting algebraic structures, that are analogous to, or rather an extension of, the 2d vertex operator algebras that have now become familiar familiar in the context of 4d N=2 theories.
Posted by: IC
Wed
22 Jun 2022
Hydrodynamization, asymptotics and the early to late time interpolation in relativistic hydrodynamics
๐ London
Ines Varela Aniceto
(University of Southampton )
Abstract:
Dissipative relativistic hydrodynamics is expected to describe the late times, thermalised behaviour of strongly coupled fluids such as a strongly coupled super Yang-Mills plasma. These systems are then accurately described by a hydrodynamic series expansion in small gradients. Surprisingly, this hydrodynamic expansion is accurate even when the systems are still quite anisotropic: the non-hydrodynamic modes governing the non-equilibrium behaviour at very early-times become exponentially close to the hydrodynamic solution in an early process called hydrodynamization.
This early success is intimately related with the fact that the hydrodynamic expansion is asymptotic. The theory of transseries and resurgence explicitly shows how the non hydrodynamic modes are in fact encoded in this late-time expansion. In this talk we will focus on a MIS-type model and use exponentially accurate summations of the the late-time resurgent transseries to recover the behaviour of the fluid before hydrodynamisation, and effectively match it to any given initial non-equilibrium condition. We will further show that such summations can provide analytic predictions beyond the late time regime.
Dissipative relativistic hydrodynamics is expected to describe the late times, thermalised behaviour of strongly coupled fluids such as a strongly coupled super Yang-Mills plasma. These systems are then accurately described by a hydrodynamic series expansion in small gradients. Surprisingly, this hydrodynamic expansion is accurate even when the systems are still quite anisotropic: the non-hydrodynamic modes governing the non-equilibrium behaviour at very early-times become exponentially close to the hydrodynamic solution in an early process called hydrodynamization.
This early success is intimately related with the fact that the hydrodynamic expansion is asymptotic. The theory of transseries and resurgence explicitly shows how the non hydrodynamic modes are in fact encoded in this late-time expansion. In this talk we will focus on a MIS-type model and use exponentially accurate summations of the the late-time resurgent transseries to recover the behaviour of the fluid before hydrodynamisation, and effectively match it to any given initial non-equilibrium condition. We will further show that such summations can provide analytic predictions beyond the late time regime.
Posted by: andrea
Wed
22 Jun 2022
Spacetime, Quantum Mechanics and Scattering Amplitudes
๐ London
Nima Arkani-Hamed
(IAS)
Abstract:
As part of the SAGEX Closing Meeting being held at Queen Mary's University of London in June 2022, we are delighted that world-renowned theoretical physicist, Professor Nima Arkani-Hamed will deliver the meeting's colloquium.
We welcome undergraduate and postgraduate students, and researchers and academics to attend this exciting event.
Please register at:
https://www.eventbrite.co.uk/e/sagex-colloquium-nima-arkani-hamed-tickets-256058035477
As part of the SAGEX Closing Meeting being held at Queen Mary's University of London in June 2022, we are delighted that world-renowned theoretical physicist, Professor Nima Arkani-Hamed will deliver the meeting's colloquium.
We welcome undergraduate and postgraduate students, and researchers and academics to attend this exciting event.
Please register at:
https://www.eventbrite.co.uk/e/sagex-colloquium-nima-arkani-hamed-tickets-256058035477
Posted by: QMW
Wed
15 Jun 2022
Bootstrap for matrix models and lattice Yang-Mills theory
๐ London
Vladimir Kazakov
(ENS Paris)
Abstract:
I will speak about my recent work with Zechuan Zheng where we study the SU(Nc) lattice Yang-Mills theory in the t Hooft limit Nc -> infinity, at dimensions D=2,3,4, via the numerical bootstrap method. It combines the Makeenko-Migdal loop equations, with the cut-off L on maximal length of wilson loops, and the positivity conditions on certain correlation matrices. We thus obtain rigorous upper and lower bounds on plaquette average at various couplings. The results are quickly improving with the increase of the cutoff L. In particular, for D=4 and L=16, the upper bound data in the most interesting weak coupling phase are not far from the Monte-Carlo results and they reproduce well the 3-loop perturbation theory. We also attempt to extract the information about the gluon condensate from this data. Our results suggest that bootstrap can provide a tangible alternative to, so far uncontested, Monte Carlo approach. I will also mention our bootstrap results for an "unsolvable" two-matrix model in the large N limit, where this method appears to be superior in efficiency over Monte Carlo.
I will speak about my recent work with Zechuan Zheng where we study the SU(Nc) lattice Yang-Mills theory in the t Hooft limit Nc -> infinity, at dimensions D=2,3,4, via the numerical bootstrap method. It combines the Makeenko-Migdal loop equations, with the cut-off L on maximal length of wilson loops, and the positivity conditions on certain correlation matrices. We thus obtain rigorous upper and lower bounds on plaquette average at various couplings. The results are quickly improving with the increase of the cutoff L. In particular, for D=4 and L=16, the upper bound data in the most interesting weak coupling phase are not far from the Monte-Carlo results and they reproduce well the 3-loop perturbation theory. We also attempt to extract the information about the gluon condensate from this data. Our results suggest that bootstrap can provide a tangible alternative to, so far uncontested, Monte Carlo approach. I will also mention our bootstrap results for an "unsolvable" two-matrix model in the large N limit, where this method appears to be superior in efficiency over Monte Carlo.
Posted by: andrea
Tue
14 Jun 2022
CosmoLattice - The Art of Simulating the Early Universe
Daniel Figueroa
(IFIC (CSIC/UV), Valencia, Spain)
Abstract:
In this talk we will introduce CosmoLattice, a modern code for simulating the non-linear dynamics of interactive scalar-gauge theories in an expanding universe. As a demonstration of its power we will solve three very different problems of early Universe cosmology: i) the generation and use of gravitational waves as a probe of particle couplings, ii) the dynamics of non-minimally coupled scalar fields in the Jordan frame, and iii) the non-linear dynamics of helical gauge field production during the last efoldings of axion-inflation
In this talk we will introduce CosmoLattice, a modern code for simulating the non-linear dynamics of interactive scalar-gauge theories in an expanding universe. As a demonstration of its power we will solve three very different problems of early Universe cosmology: i) the generation and use of gravitational waves as a probe of particle couplings, ii) the dynamics of non-minimally coupled scalar fields in the Jordan frame, and iii) the non-linear dynamics of helical gauge field production during the last efoldings of axion-inflation
Posted by: IC
May 2022
Tue
31 May 2022
Testing massive fields during inflation with the cosmic microwave background
Matteo Braglia
(IFT/UAM)
Abstract:
Massive fields oscillating around their minima produce specific
oscillatory patterns in the density perturbations that record the time
dependence of the scale factor in the primordial Universe (hence the
name 'Primordial Standard Clocks'). In this talk, I present recent
developments on the model building of inflationary classical
primordial standard clocks (CPSC) and emphasize their observable
consequences. I then present constraints on these models from the
latest Planck temperature and polarization data and show how CPSC can
address anomalies at different multipoles. Finally, I discuss the
prospects for detecting CPSCs with upcoming CMB missions and to
distinguish them from other types of features.
Massive fields oscillating around their minima produce specific
oscillatory patterns in the density perturbations that record the time
dependence of the scale factor in the primordial Universe (hence the
name 'Primordial Standard Clocks'). In this talk, I present recent
developments on the model building of inflationary classical
primordial standard clocks (CPSC) and emphasize their observable
consequences. I then present constraints on these models from the
latest Planck temperature and polarization data and show how CPSC can
address anomalies at different multipoles. Finally, I discuss the
prospects for detecting CPSCs with upcoming CMB missions and to
distinguish them from other types of features.
Posted by: IC
Thu
26 May 2022
Phase structure of theories with 8 supercharges – Higgs branch
๐ London
Amihay Hanany
(Imperial College)
Abstract:
The moduli space of Supersymmetric gauge theories with 8 supercharges has a rich structure of symplectic singularities associated with degenerations in which additional massless states arise. These are neatly arranged into phase diagrams that encode the different sets of massless states, with information on the moduli that are needed to be tuned in order to move from one phase to another. We will present results from studies of families of quivers, including those on the affine grassmanian of finite dimensional Lie algebras.
; part of the London TQFT Journal Club (please register at https://london-tqft.vercel.app)
The moduli space of Supersymmetric gauge theories with 8 supercharges has a rich structure of symplectic singularities associated with degenerations in which additional massless states arise. These are neatly arranged into phase diagrams that encode the different sets of massless states, with information on the moduli that are needed to be tuned in order to move from one phase to another. We will present results from studies of families of quivers, including those on the affine grassmanian of finite dimensional Lie algebras.
; part of the London TQFT Journal Club (please register at https://london-tqft.vercel.app)
Posted by: QMW
Thu
26 May 2022
Duality Defects in Quantum Field Theory
๐ London
Clay Cordova
(Chicago)
Abstract:
For any quantum system invariant under gauging a higher-form global symmetry, we construct a non-invertible topological defect by gauging in only half of spacetime. This generalizes the Kramers-Wannier duality line in 1+1 dimensions to higher spacetime dimensions. We focus on the case of a one-form symmetry in 3+1 dimensions, and determine the fusion rule. We give an explicit realization of this duality defect in the free Maxwell theory. The duality defect is realized by a Chern-Simons coupling between the gauge fields from the two sides.
[for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
For any quantum system invariant under gauging a higher-form global symmetry, we construct a non-invertible topological defect by gauging in only half of spacetime. This generalizes the Kramers-Wannier duality line in 1+1 dimensions to higher spacetime dimensions. We focus on the case of a one-form symmetry in 3+1 dimensions, and determine the fusion rule. We give an explicit realization of this duality defect in the free Maxwell theory. The duality defect is realized by a Chern-Simons coupling between the gauge fields from the two sides.
[for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Tue
24 May 2022
Criticality in Eternal Inflation
Justin Khoury
(University of Pennsylvania)
Abstract:
The string landscape, together with the mechanism of eternal inflation for populating vacua, leads to the seemingly inescapable conclusion that we are part of a vast multiverse. As an inhabitant of the multiverse, how should we reason probabilistically about the expected physical properties of our observable universe? Probabilities in eternal inflation are usually defined in terms of frequencies, but this approach has failed to yield a unique answer. In this talk, I will present a different approach to the problem, based on Bayesian reasoning. By adopting the least informative priors on the model parameters, we will be led to well-defined, time-reparametrization invariant (and non-anthropic) probabilities for occupying different vacua. Remarkably, these probabilities favor vacua whose surrounding landscape topography is that of a deep valley or funnel, akin to folding funnels of naturally-occurring proteins. Furthermore, by modeling the landscape of vacua as a random network, I will show that our probabilities favor regions that are close to the directed percolation phase transition. As usual, the predictive power of criticality lies in scale invariant observables characterized by critical exponents. As an example, I will show that the probability distribution for the cosmological constant is power-law, with a particular critical exponent, and favors a naturally small and positive vacuum energy. Tantalizingly, this hints at a deep connection between non-equilibrium critical phenomena on the landscape and the near-criticality of our universe.
The string landscape, together with the mechanism of eternal inflation for populating vacua, leads to the seemingly inescapable conclusion that we are part of a vast multiverse. As an inhabitant of the multiverse, how should we reason probabilistically about the expected physical properties of our observable universe? Probabilities in eternal inflation are usually defined in terms of frequencies, but this approach has failed to yield a unique answer. In this talk, I will present a different approach to the problem, based on Bayesian reasoning. By adopting the least informative priors on the model parameters, we will be led to well-defined, time-reparametrization invariant (and non-anthropic) probabilities for occupying different vacua. Remarkably, these probabilities favor vacua whose surrounding landscape topography is that of a deep valley or funnel, akin to folding funnels of naturally-occurring proteins. Furthermore, by modeling the landscape of vacua as a random network, I will show that our probabilities favor regions that are close to the directed percolation phase transition. As usual, the predictive power of criticality lies in scale invariant observables characterized by critical exponents. As an example, I will show that the probability distribution for the cosmological constant is power-law, with a particular critical exponent, and favors a naturally small and positive vacuum energy. Tantalizingly, this hints at a deep connection between non-equilibrium critical phenomena on the landscape and the near-criticality of our universe.
Posted by: IC
Thu
19 May 2022
Gravitational Edge Modes, Coadjoint Orbits, Hydrodynamics and matrix model
๐ London
Laurent Freidel
(Perimeter)
Abstract:
In this talk I will present an overview of the local holography program which links the quantization of gravity with the representation theory of infinite dimensional symmetry groups attached to codimension 2 surfaces: the corners. I will present in detail the corner symmetry group for 4d gravity and show its connection with the symmetry algebra of perfect fluids. As a step towards quantization, I will recall the importance of the co-adjoint orbit method and I will derive a complete classification of the positive-area coadjoint orbits of this group for corners that are a 2-sphere. I will also show that a deformation of this symmetry group naturally involves matrix model as a quantum regulator. If time permits I will mention some connections these results have with celestial holography and the higher spin asymptotic symmetry group. [for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
In this talk I will present an overview of the local holography program which links the quantization of gravity with the representation theory of infinite dimensional symmetry groups attached to codimension 2 surfaces: the corners. I will present in detail the corner symmetry group for 4d gravity and show its connection with the symmetry algebra of perfect fluids. As a step towards quantization, I will recall the importance of the co-adjoint orbit method and I will derive a complete classification of the positive-area coadjoint orbits of this group for corners that are a 2-sphere. I will also show that a deformation of this symmetry group naturally involves matrix model as a quantum regulator. If time permits I will mention some connections these results have with celestial holography and the higher spin asymptotic symmetry group. [for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
19 May 2022
Factorization and global symmetries in holography
๐ London
Francesco Benini
(SISSA)
Abstract:
There exist low-dimensional models of holography in which the bulk
gravitational theory is dual to an ensemble average of boundary
quantum field theories (as opposed to a single theory). In the case of
three-dimensional gravitational theories based on topological field
theories, we draw a connection between the ensemble averaging (and the
lack of factorization of the partition function) and the presence of
global symmetries. Once the global symmetries are removed (by a
suitable gauging procedure), the gravitational theory behaves as a
unitary quantum system.; Part of London TQFT Journal Club; please register at https://www.london-tqft.co.uk;
There exist low-dimensional models of holography in which the bulk
gravitational theory is dual to an ensemble average of boundary
quantum field theories (as opposed to a single theory). In the case of
three-dimensional gravitational theories based on topological field
theories, we draw a connection between the ensemble averaging (and the
lack of factorization of the partition function) and the presence of
global symmetries. Once the global symmetries are removed (by a
suitable gauging procedure), the gravitational theory behaves as a
unitary quantum system.; Part of London TQFT Journal Club; please register at https://www.london-tqft.co.uk;
Posted by: QMW
Wed
18 May 2022
Bootstrapping the Maldacena Wilson line at strong coupling
๐ London
Pietro Ferrero
(Mathematical Institute, Oxford University)
Abstract:
The insertion of local operators along a straight Maldacena Wilson line in planar N=4 super Yang Mills defines a defect supersymmetric conformal field theory in one dimension. This is a simple but interesting setup where one can combine field theory techniques such as bootstrap, integrability and localization, aiming at a full solution of a non-trivial quantum mechanical system. I will adopt a bootstrap approach and study correlation functions of local operators for large t Hooft coupling, where the system is dual to an open superstring in \(AdS_5 \times S^5\). I will present results for the four-point function of the displacement multiplet of the 1d defect CFT corresponding to three-loop diagrams in AdS, which are obtained using a suitable position-space ansatz and after considering a large system of mixed correlators. The problem is made particularly hard by the large degeneracy of operators at strong coupling, which we solve by taking into account four-point functions with external unprotected operators. The simple 1d kinematics is an ideal toy model for bootstrap techniques of interest for higher-dimensional cases as well. The seminar will be based on published as well as ongoing work with Carlo Meneghelli (see arxiv:2103.10440).
The insertion of local operators along a straight Maldacena Wilson line in planar N=4 super Yang Mills defines a defect supersymmetric conformal field theory in one dimension. This is a simple but interesting setup where one can combine field theory techniques such as bootstrap, integrability and localization, aiming at a full solution of a non-trivial quantum mechanical system. I will adopt a bootstrap approach and study correlation functions of local operators for large t Hooft coupling, where the system is dual to an open superstring in \(AdS_5 \times S^5\). I will present results for the four-point function of the displacement multiplet of the 1d defect CFT corresponding to three-loop diagrams in AdS, which are obtained using a suitable position-space ansatz and after considering a large system of mixed correlators. The problem is made particularly hard by the large degeneracy of operators at strong coupling, which we solve by taking into account four-point functions with external unprotected operators. The simple 1d kinematics is an ideal toy model for bootstrap techniques of interest for higher-dimensional cases as well. The seminar will be based on published as well as ongoing work with Carlo Meneghelli (see arxiv:2103.10440).
Posted by: andrea
Tue
17 May 2022
dS vs Quintessence: who sinks in the swampland?
Michele Cicoli
(Bologna University)
Abstract:
I will discuss different theoretical and phenomenological challenges of quintessence model building in string theory in order to be able to give an informed answer to the question in the title.
I will discuss different theoretical and phenomenological challenges of quintessence model building in string theory in order to be able to give an informed answer to the question in the title.
Posted by: IC
Thu
12 May 2022
Tenfold Way for Holography : AdS/CFT and Beyond
๐ London
Vladimir Dobrev
(Bulgarian Academy of Sciences)
Abstract:
The main purpose of the present talk is to lay the foundations of generalizing the AdS/CFT (holography) idea beyond the conformal setting, where it is very natural. The main tool is to find suitable realizations of the bulk and boundary via group theory. We use all ten families of classical real semisimple Lie groups G and Lie algebras g. For this are used several group and algebra decompositions: the global Iwasawa decomposition and the local Bruhat and Sekiguchi decomposititions, which we introduce first on easy examples. The same analysis is applied to the exceptional real semisimple Lie algebras. We present the boundary-to-bulk operators first in the Euclidean conformal setting
and then outline the various generalizations.
The main purpose of the present talk is to lay the foundations of generalizing the AdS/CFT (holography) idea beyond the conformal setting, where it is very natural. The main tool is to find suitable realizations of the bulk and boundary via group theory. We use all ten families of classical real semisimple Lie groups G and Lie algebras g. For this are used several group and algebra decompositions: the global Iwasawa decomposition and the local Bruhat and Sekiguchi decomposititions, which we introduce first on easy examples. The same analysis is applied to the exceptional real semisimple Lie algebras. We present the boundary-to-bulk operators first in the Euclidean conformal setting
and then outline the various generalizations.
Posted by: QMW
Wed
11 May 2022
Celestial Operator Product Expansions and w(1+infinity) Symmetry for All Spins
๐ London
Elizabeth Himwich
(Harvard)
Abstract:
The operator product expansion of massless celestial primary operators of arbitrary spin is investigated. Poincarรยฉ symmetry is found to imply a set of recursion relations on the operator product expansion coefficients of the leading singular terms at tree-level in a holomorphic limit. The symmetry constraints are solved by an Euler beta function with arguments that depend simply on the right-moving conformal weights of the operators in the product. These symmetry-derived coefficients are shown not only to match precisely those arising from momentum-space tree-level collinear limits, but also to obey an infinite number of additional symmetry transformations that respect the algebra of w(1+infinity). In tree-level minimally-coupled gravitational theories, celestial currents are constructed from light transforms of conformally soft gravitons and found to generate the action of w(1+infinity) on arbitrary massless celestial primaries. Results include operator product expansion coefficients for fermions as well as those arising from higher-derivative non-minimal couplings of gluons and gravitons.
The operator product expansion of massless celestial primary operators of arbitrary spin is investigated. Poincarรยฉ symmetry is found to imply a set of recursion relations on the operator product expansion coefficients of the leading singular terms at tree-level in a holomorphic limit. The symmetry constraints are solved by an Euler beta function with arguments that depend simply on the right-moving conformal weights of the operators in the product. These symmetry-derived coefficients are shown not only to match precisely those arising from momentum-space tree-level collinear limits, but also to obey an infinite number of additional symmetry transformations that respect the algebra of w(1+infinity). In tree-level minimally-coupled gravitational theories, celestial currents are constructed from light transforms of conformally soft gravitons and found to generate the action of w(1+infinity) on arbitrary massless celestial primaries. Results include operator product expansion coefficients for fermions as well as those arising from higher-derivative non-minimal couplings of gluons and gravitons.
Posted by: andrea
Fri
6 May 2022
(A)dS Taub-NUT and exact black bounces with scalar hair
๐ London
Adolfo R. Cisterna Roa
(U. of Tarapaca/ U. of Trento)
Abstract:
We present a new family of exact four-dimensional Taub-NUT spacetimes in Einstein-รโบ theory supplemented with a conformally coupled scalar field exhibiting a power-counting super-renormalizable potential. Our configurations are constructed in the following manner: A solution of a conformally coupled theory with a conformal potential, henceforth the seed (gรยผรยฝ,รโ ), is transformed by the action of a specific change of frame in addition with a simultaneous shift of the seed scalar field. The conformal factor of the transformation and the shift are both affine functions of the original scalar รโ . The new configuration, (รกยธยกรยผรยฝ , รโ รโ), solves the field equations of a conformally coupled theory with the extended aforementioned super-renormalizable potential, this under the presence of an effective cosmological constant. The new spectrum of solutions is notoriously enhanced with respect to the original seed containing regular black holes, wormholes, and bouncing cosmologies. We highlight the existence of two types of exact black bounces given by de Sitter and anti-de Sitter geometries that transit across three different configurations each. The de Sitter geometries transit from a regular black hole with event and cosmological horizons to a bouncing cosmology that connects two de Sitter Universes with different values of the asymptotic cosmological constant. An intermediate phase, which might be represented by two different configurations, takes place. These configurations are given by a de Sitter wormhole or by a bouncing cosmology that connects two de Sitter Universes, both under the presence of a cosmological horizon. On the other hand, the anti-de Sitter geometries transit from a regular black hole with inner and event horizons to a wormhole that connects two asymptotic boundaries with different constant curvatures. The intermediate phase is given in this case by an anti-de Sitter regular black hole with a single event horizon. This regular black hole might appear in two different configurations. As a regular anti-de Sitter black hole inside of an anti-de Sitter wormhole or as an anti-de Sitter regular black hole with a cosmological bounce in its interior. All these geometries are shown to be smoothly connected by the mass parameter only. Other standard stationary black holes, bouncing cosmologies and wormholes are also identified.
We present a new family of exact four-dimensional Taub-NUT spacetimes in Einstein-รโบ theory supplemented with a conformally coupled scalar field exhibiting a power-counting super-renormalizable potential. Our configurations are constructed in the following manner: A solution of a conformally coupled theory with a conformal potential, henceforth the seed (gรยผรยฝ,รโ ), is transformed by the action of a specific change of frame in addition with a simultaneous shift of the seed scalar field. The conformal factor of the transformation and the shift are both affine functions of the original scalar รโ . The new configuration, (รกยธยกรยผรยฝ , รโ รโ), solves the field equations of a conformally coupled theory with the extended aforementioned super-renormalizable potential, this under the presence of an effective cosmological constant. The new spectrum of solutions is notoriously enhanced with respect to the original seed containing regular black holes, wormholes, and bouncing cosmologies. We highlight the existence of two types of exact black bounces given by de Sitter and anti-de Sitter geometries that transit across three different configurations each. The de Sitter geometries transit from a regular black hole with event and cosmological horizons to a bouncing cosmology that connects two de Sitter Universes with different values of the asymptotic cosmological constant. An intermediate phase, which might be represented by two different configurations, takes place. These configurations are given by a de Sitter wormhole or by a bouncing cosmology that connects two de Sitter Universes, both under the presence of a cosmological horizon. On the other hand, the anti-de Sitter geometries transit from a regular black hole with inner and event horizons to a wormhole that connects two asymptotic boundaries with different constant curvatures. The intermediate phase is given in this case by an anti-de Sitter regular black hole with a single event horizon. This regular black hole might appear in two different configurations. As a regular anti-de Sitter black hole inside of an anti-de Sitter wormhole or as an anti-de Sitter regular black hole with a cosmological bounce in its interior. All these geometries are shown to be smoothly connected by the mass parameter only. Other standard stationary black holes, bouncing cosmologies and wormholes are also identified.
Posted by: andrea
Thu
5 May 2022
New Lagrangian realisations of 6d SCFTs
๐ London
Rishi Mouland
(Cambridge)
Abstract:
Since the existence of interacting SCFTs in six dimensions was first inferred by string theory, many have sought a Lagrangian construction of such models. With this goal in mind, in this talk I will introduce some curious supersymmetric Lagrangian gauge theories in five dimensions. These models exhibit an Omega-deformed non-relativistic conformal symmetry, and have a single, discrete coupling. Crucially, I will argue that these models in fact capture the dynamics of six-dimensional (2,0) and (1,0) SCFTs, through a solitonic enhancement mechanism analogous to that of the ABJM model. I will finally speculate on the utility of the models, including through the fashionable paradigms of integrability and localisation.
Since the existence of interacting SCFTs in six dimensions was first inferred by string theory, many have sought a Lagrangian construction of such models. With this goal in mind, in this talk I will introduce some curious supersymmetric Lagrangian gauge theories in five dimensions. These models exhibit an Omega-deformed non-relativistic conformal symmetry, and have a single, discrete coupling. Crucially, I will argue that these models in fact capture the dynamics of six-dimensional (2,0) and (1,0) SCFTs, through a solitonic enhancement mechanism analogous to that of the ABJM model. I will finally speculate on the utility of the models, including through the fashionable paradigms of integrability and localisation.
Posted by: QMW
Thu
5 May 2022
Comments on Wilson Lines in Massless Gauge Theories
๐ London
Zohar Komargodski
(Simons Center for Geometry and Physics)
Abstract:
Note unusual time. part of London TQFT Journal Club (please register at https://london-tqft.co.uk);
Note unusual time. part of London TQFT Journal Club (please register at https://london-tqft.co.uk);
Posted by: QMW
Wed
4 May 2022
w-infinity Symmetry of Quantum Self-Dual Gravity
๐ London
Jakob Salzer
(Brussels U.)
Abstract:
General Relativity in asymptotically flat spacetimes gives rise to an infinite number of symmetries which form the celebrated BMS group comprising superrotations and supertranslations. These symmetries are closely related to soft theorems of gravitational scattering amplitudes. Recently it was shown that supertranslations and superrotations are only the lowest levels of a whole tower of symmetries of tree level gravitational scattering amplitudes that form a w_{1+\infty} algebra. The fate of this symmetry once loop effects are taken into account is currently unknown.
In this talk I will review the emergence of this symmetry algebra based on the celestial CFT program and argue that the w_{1+\infty} algebra persists quantum corrections in self-dual gravity.
This talk is based on 2111.10392 with A.Ball, S. Narayanan, and A. Strominger.
General Relativity in asymptotically flat spacetimes gives rise to an infinite number of symmetries which form the celebrated BMS group comprising superrotations and supertranslations. These symmetries are closely related to soft theorems of gravitational scattering amplitudes. Recently it was shown that supertranslations and superrotations are only the lowest levels of a whole tower of symmetries of tree level gravitational scattering amplitudes that form a w_{1+\infty} algebra. The fate of this symmetry once loop effects are taken into account is currently unknown.
In this talk I will review the emergence of this symmetry algebra based on the celestial CFT program and argue that the w_{1+\infty} algebra persists quantum corrections in self-dual gravity.
This talk is based on 2111.10392 with A.Ball, S. Narayanan, and A. Strominger.
Posted by: andrea
April 2022
Thu
28 Apr 2022
Entanglement in the quantum Hall matrix model
๐ London
Sean Hartnoll
(Cambridge)
Abstract:
Quantum mechanical theories describing large N by N matrices of oscillators can lead to an emergent space as N -> infinity. In the most fully fledged version, the emergent space is dynamical and gravitating. However, there are also simpler, lower dimensional versions of this phenomenon. One of the simplest occurs in the so-called quantum Hall matrix model, in which a 2 dimensional space emerges and supports Chern-Simons dynamics. I will describe how this solvable model leads to insights about the emergence of space from matrices. In particular, I will describe how the emergent spatial locality is reflected in the entanglement structure of the ground state of theory.
Quantum mechanical theories describing large N by N matrices of oscillators can lead to an emergent space as N -> infinity. In the most fully fledged version, the emergent space is dynamical and gravitating. However, there are also simpler, lower dimensional versions of this phenomenon. One of the simplest occurs in the so-called quantum Hall matrix model, in which a 2 dimensional space emerges and supports Chern-Simons dynamics. I will describe how this solvable model leads to insights about the emergence of space from matrices. In particular, I will describe how the emergent spatial locality is reflected in the entanglement structure of the ground state of theory.
Posted by: QMW
Thu
28 Apr 2022
Comments on Summing over Bordisms in TQFT
Anindya Banerjee
(Rutgers)
Abstract:
Recent works in quantum gravity, motivated by the factorization problem and baby universes, have considered sums over bordisms with fixed boundaries in topological quantum field theory. I will discuss this construction, its scope and its limitations, and describe the total amplitude in this class of theories in terms of a curious splitting formula; Part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.co.uk)
Recent works in quantum gravity, motivated by the factorization problem and baby universes, have considered sums over bordisms with fixed boundaries in topological quantum field theory. I will discuss this construction, its scope and its limitations, and describe the total amplitude in this class of theories in terms of a curious splitting formula; Part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.co.uk)
Posted by: QMW
Tue
26 Apr 2022
Constraining the fundamental theory: cosmological observations and theoretical consistency.
Anna Tokareva
(Imperial College London)
Abstract:
I can formulate the purpose of my research as an attempt to look to the quantum gravity through both the theoretical and observational windows. My previous research was mainly dedicated to obtaining both observational predictions and theoretical constraints for the models of inflation which can be stated as 'minimal'. They contain only the fields which are proved to exist: Higgs field and gravity. As the results of this work, we proved the self-consistency and investigated the reheating mechanism in a model describing inflation driven by the interplay of Higgs and gravity. My recent research is more focused on the theoretical window to the nature of quantum gravity based on the scattering amplitudes and dispersive relations. The scattering amplitudes through the graviton exchange contain the IR singularities in forward limit. The divergences at \(t\rightarrow 0\) can be cancelled in the dispersive relation only if the UV limit of the amplitude is tuned in a specific way which establishes the non-trivial connection between UV and IR forms of the amplitude. We show that this connection can be expressed in terms of the Laplace transform and it can give an information about the UV amplitude in the limit \(t \log{s}\rightarrow 0\). We discuss the implications of this approach for QED with gravity.
I can formulate the purpose of my research as an attempt to look to the quantum gravity through both the theoretical and observational windows. My previous research was mainly dedicated to obtaining both observational predictions and theoretical constraints for the models of inflation which can be stated as 'minimal'. They contain only the fields which are proved to exist: Higgs field and gravity. As the results of this work, we proved the self-consistency and investigated the reheating mechanism in a model describing inflation driven by the interplay of Higgs and gravity. My recent research is more focused on the theoretical window to the nature of quantum gravity based on the scattering amplitudes and dispersive relations. The scattering amplitudes through the graviton exchange contain the IR singularities in forward limit. The divergences at \(t\rightarrow 0\) can be cancelled in the dispersive relation only if the UV limit of the amplitude is tuned in a specific way which establishes the non-trivial connection between UV and IR forms of the amplitude. We show that this connection can be expressed in terms of the Laplace transform and it can give an information about the UV amplitude in the limit \(t \log{s}\rightarrow 0\). We discuss the implications of this approach for QED with gravity.
Posted by: IC
Thu
21 Apr 2022
RG flows on line defects
๐ London
Gabriel Cuomo
(Simons Center for Geometry and Physics)
Abstract:
I will discuss line defects in d-dimensional Conformal Field Theories (CFTs). I will first review the definitions and some properties of defect CFTs and defect RG flows, including a recent result on the monotonicity of the defect RG flow. I will then discuss in detail two examples relevant for three-dimensional critical systems: magnetic field defects, which arise from a localized external field in a lattice system, and spin defects, that describe doping impurities in magnets. I will show in particular that impurities with large spin are รขโฌลeffectivelyรขโฌโขรขโฌโข equivalent to a magnetic field defect. I will close with a comment on Wilson lines in conformal gauge theories; part of London TQFT Journal Club (please register at https://london-tqft.co.uk);
I will discuss line defects in d-dimensional Conformal Field Theories (CFTs). I will first review the definitions and some properties of defect CFTs and defect RG flows, including a recent result on the monotonicity of the defect RG flow. I will then discuss in detail two examples relevant for three-dimensional critical systems: magnetic field defects, which arise from a localized external field in a lattice system, and spin defects, that describe doping impurities in magnets. I will show in particular that impurities with large spin are รขโฌลeffectivelyรขโฌโขรขโฌโข equivalent to a magnetic field defect. I will close with a comment on Wilson lines in conformal gauge theories; part of London TQFT Journal Club (please register at https://london-tqft.co.uk);
Posted by: QMW
Thu
21 Apr 2022
Characterization and Classification of Fermionic Symmetry Enriched Phases
๐ London
David Aasen
(UCSB)
Abstract:
Topological phases can be divided into two classes corresponding to whether the microscopic degrees of freedom supporting the phase are purely bosonic (e.g., spins or qubits) or whether they include fermions (e.g., electrons). Imposing a symmetry on a topological phase enriches the classification by restricting and possibly fracturing the phase space. Fermionic topological phases additionally include an underlying fermionic particle of the system, the physical fermion. This talk will present recent results on the algebraic structure and classification of fermionic topological phases with on-site unitary symmetry using G-crossed braided tensor categories. I will emphasize the new obstructions which appear, contrast them with their bosonic counterparts, and provide a complete characterization of all symmetric unobstructed invertible fermionic phases. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Topological phases can be divided into two classes corresponding to whether the microscopic degrees of freedom supporting the phase are purely bosonic (e.g., spins or qubits) or whether they include fermions (e.g., electrons). Imposing a symmetry on a topological phase enriches the classification by restricting and possibly fracturing the phase space. Fermionic topological phases additionally include an underlying fermionic particle of the system, the physical fermion. This talk will present recent results on the algebraic structure and classification of fermionic topological phases with on-site unitary symmetry using G-crossed braided tensor categories. I will emphasize the new obstructions which appear, contrast them with their bosonic counterparts, and provide a complete characterization of all symmetric unobstructed invertible fermionic phases. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Wed
20 Apr 2022
Possible kinematics for flat space holography
๐ London
Jose Figueroa-O'Farrill
(University of Edinburgh)
Abstract:
I will discuss recent and ongoing work with Emil Have, Stefan Prohazka and Jakob Salzer on possible kinematics for flat space holography. I will discuss how a seemingly novel projective compactification of Minkowski spacetime reveals a rich asymptotic geometry homogeneous under the Poincare group and including the blow-ups at spatial and timelike infinities as well as a novel four-dimensional space intimately associated to null infinity. This allows for novel geometric descriptions of the Minkowski asymptotic geometries and gives us a glimpse of the asymptotic geometry of asymptotically flat spaces.
I will discuss recent and ongoing work with Emil Have, Stefan Prohazka and Jakob Salzer on possible kinematics for flat space holography. I will discuss how a seemingly novel projective compactification of Minkowski spacetime reveals a rich asymptotic geometry homogeneous under the Poincare group and including the blow-ups at spatial and timelike infinities as well as a novel four-dimensional space intimately associated to null infinity. This allows for novel geometric descriptions of the Minkowski asymptotic geometries and gives us a glimpse of the asymptotic geometry of asymptotically flat spaces.
Posted by: andrea
Thu
14 Apr 2022
Lattice QCD at nonzero temperature
๐ London
Gert Aarts
(Swansea U.)
Abstract:
QCD undergoes a transition from the confined phase (hadron gas) to a deconfined quark-gluon plasma at a temperature of about 155 MeV. This phenomenon can be investigated in relativistic heavy-ion experiments and studied theoretically, using e.g. simulations of QCD discretised on a space-time lattice. In this talk, I will review some aspects of QCD at nonzero temperature, with an emphasis on results obtained by our lattice QCD collaboration. Very recently, machine learning has been introduced as a new tool to study lattice field theory. In the final part, I will present some results of applications of machine learning to phase transitions in statistical field theory.
QCD undergoes a transition from the confined phase (hadron gas) to a deconfined quark-gluon plasma at a temperature of about 155 MeV. This phenomenon can be investigated in relativistic heavy-ion experiments and studied theoretically, using e.g. simulations of QCD discretised on a space-time lattice. In this talk, I will review some aspects of QCD at nonzero temperature, with an emphasis on results obtained by our lattice QCD collaboration. Very recently, machine learning has been introduced as a new tool to study lattice field theory. In the final part, I will present some results of applications of machine learning to phase transitions in statistical field theory.
Posted by: QMW
Thu
14 Apr 2022
Line Operators in Chern-Simons-Matter Theories and Bosonization in Three Dimensions
Amit Sever
(Tel Aviv University)
Abstract:
We study Chern-Simons theories at large N with either bosonic or fermionic matter in the fundamental representation. The most fundamental operators in these theories are mesonic line operators, the simplest example being Wilson lines ending on fundamentals. We classify the conformal line operators along an arbitrary smooth path as well as the spectrum of conformal dimensions and transverse spins of their boundary operators at finite 't Hooft coupling. These line operators are shown to satisfy first-order chiral evolution equations, in which a smooth variation of the path is given by a factorized product of two line operators. We argue that this equation together with the spectrum of boundary operators are sufficient to uniquely determine the expectation values of these operators. We demonstrate this by bootstrapping the two-point function of the displacement operator on a straight line. We show that the line operators in the theory of bosons and the theory of fermions satisfy the same evolution equation and have the same spectrum of boundary operators. ––- Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. Link emailed on Tuesday.
We study Chern-Simons theories at large N with either bosonic or fermionic matter in the fundamental representation. The most fundamental operators in these theories are mesonic line operators, the simplest example being Wilson lines ending on fundamentals. We classify the conformal line operators along an arbitrary smooth path as well as the spectrum of conformal dimensions and transverse spins of their boundary operators at finite 't Hooft coupling. These line operators are shown to satisfy first-order chiral evolution equations, in which a smooth variation of the path is given by a factorized product of two line operators. We argue that this equation together with the spectrum of boundary operators are sufficient to uniquely determine the expectation values of these operators. We demonstrate this by bootstrapping the two-point function of the displacement operator on a straight line. We show that the line operators in the theory of bosons and the theory of fermions satisfy the same evolution equation and have the same spectrum of boundary operators. ––- Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. Link emailed on Tuesday.
Posted by: andrea
Thu
14 Apr 2022
Simulation of quantum field theories by quantum computers
Zhenghan Wang
(Microsoft Station Q and UC Santa Barbara)
Abstract:
The quantum Church-Turing thesis would imply that there is a unique model of quantum computing. It follows that quantum computers could simulate quantum field theories efficiently.After a review on the simulation of topological quantum field theories, we will focus on a lattice approach to conformal field theories from anyonic chains.; it will be possible to follow this talk online (please register at https://london-tqft.co.uk)
The quantum Church-Turing thesis would imply that there is a unique model of quantum computing. It follows that quantum computers could simulate quantum field theories efficiently.After a review on the simulation of topological quantum field theories, we will focus on a lattice approach to conformal field theories from anyonic chains.; it will be possible to follow this talk online (please register at https://london-tqft.co.uk)
Posted by: QMW
Wed
13 Apr 2022
Swampland Conjectures from Finiteness of Black Hole Entropy
๐ London
Irene Valenzuela
(CERN)
Abstract:
Consistency with quantum gravity can impose non-trivial constraints at low energies, even if the Planck scale is at very high energy. The Swampland program aims to determine the constraints that an effective field theory must satisfy to be consistent with a UV embedding in a quantum gravity theory. One of the most important swampland conditions is the presence of infinite towers of states becoming massless at the weak coupling/large field limits. This has been extensively tested in string theory compactifications, but a bottom-up explanation was missing. In this talk I will provide a possible explanation based on finiteness of black hole entropy. I will also explain how several wampland criteria, including the Weak Gravity Conjecture, Distance Conjecture and bounds on the finiteness of the quantum gravity vacua, may be more fundamentally a consequence of the finiteness of quantum gravity amplitudes.
Consistency with quantum gravity can impose non-trivial constraints at low energies, even if the Planck scale is at very high energy. The Swampland program aims to determine the constraints that an effective field theory must satisfy to be consistent with a UV embedding in a quantum gravity theory. One of the most important swampland conditions is the presence of infinite towers of states becoming massless at the weak coupling/large field limits. This has been extensively tested in string theory compactifications, but a bottom-up explanation was missing. In this talk I will provide a possible explanation based on finiteness of black hole entropy. I will also explain how several wampland criteria, including the Weak Gravity Conjecture, Distance Conjecture and bounds on the finiteness of the quantum gravity vacua, may be more fundamentally a consequence of the finiteness of quantum gravity amplitudes.
Posted by: andrea
Mon
11 Apr 2022
A playful intro to some modern geometry
Yang-Hui He
(LIMS and City)
Abstract:
With a view towards constructing Calabi Yau manifolds, we present some rudiments of the intersection between algebraic, differential and arithmetic geometry. Throughout we will take the opposite of the Bourbaki approach and work through explicit examples, rather than to emphasise on the theory.
With a view towards constructing Calabi Yau manifolds, we present some rudiments of the intersection between algebraic, differential and arithmetic geometry. Throughout we will take the opposite of the Bourbaki approach and work through explicit examples, rather than to emphasise on the theory.
Posted by: oxford
Thu
7 Apr 2022
Color-Kinematics Duality for 10D super-Yang-Mills from its pure spinor action
๐ London
Max Guillen
(Uppsala)
Abstract:
In this talk I will review the basic ingredients which allows one to formulate 10D super-Yang-Mills on pure spinor superspace. The respective pure spinor master action in the gauge b_{0}V = Qรลพ, will then be used to show that tree-level scattering amplitudes calculated via perturbiner methods, match those obtained from pure spinor CFT techniques. I will also discuss how to compute pure spinor kinematic numerators through the use of standard Feynman rules, and show these are described by compact expressions involving the b-ghost operator. Remarkably, it will be shown how color-kinematics duality immediately emerges in this pure spinor framework after imposing the Siegel gauge condition b_{0}V = 0.
[for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
In this talk I will review the basic ingredients which allows one to formulate 10D super-Yang-Mills on pure spinor superspace. The respective pure spinor master action in the gauge b_{0}V = Qรลพ, will then be used to show that tree-level scattering amplitudes calculated via perturbiner methods, match those obtained from pure spinor CFT techniques. I will also discuss how to compute pure spinor kinematic numerators through the use of standard Feynman rules, and show these are described by compact expressions involving the b-ghost operator. Remarkably, it will be shown how color-kinematics duality immediately emerges in this pure spinor framework after imposing the Siegel gauge condition b_{0}V = 0.
[for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
7 Apr 2022
JTbar - deformed CFTs as non-local CFTs
Monica Guica
(IPhT Saclay)
Abstract:
TTbar and JTbar - deformed CFTs provide an interesting example of non-local, yet UV-complete two-dimensional QFTs that are entirely solvable. I will start by showing that both classes of theories possess Virasoro x Virasoro or Virasoro- Kac- Moody x Virasoro - Kac- Moody symmetry. For the case of JTbar, I will discuss the classical realization of these symmetries in terms of field-dependent coordinate transformations and show how the associated generators can be used to define an analogue of "primary" operators in this non-local theory, whose correlation functions are entirely fixed in terms of those of the undeformed CFT. In particular, two and three-point functions are simply given by the corresponding momentum-space correlator in the undeformed CFT, with all dimensions replaced by particular momentum-dependent conformal dimensions. Interestingly, scattering amplitudes off the near-horizon of extremal black holes are known to take a strikingly similar form. –––– Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. Link emailed on Tuesday.
TTbar and JTbar - deformed CFTs provide an interesting example of non-local, yet UV-complete two-dimensional QFTs that are entirely solvable. I will start by showing that both classes of theories possess Virasoro x Virasoro or Virasoro- Kac- Moody x Virasoro - Kac- Moody symmetry. For the case of JTbar, I will discuss the classical realization of these symmetries in terms of field-dependent coordinate transformations and show how the associated generators can be used to define an analogue of "primary" operators in this non-local theory, whose correlation functions are entirely fixed in terms of those of the undeformed CFT. In particular, two and three-point functions are simply given by the corresponding momentum-space correlator in the undeformed CFT, with all dimensions replaced by particular momentum-dependent conformal dimensions. Interestingly, scattering amplitudes off the near-horizon of extremal black holes are known to take a strikingly similar form. –––– Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. Link emailed on Tuesday.
Posted by: andrea
Tue
5 Apr 2022
Gravitational-wave cosmology with dark sirens: state of the art and perspectives for 3G detectors
Michele Mancarella
(Geneva University)
Abstract:
Gravitational-wave (GW) cosmology provides a new way to measure the expansion history of the Universe and test General Relativity (GR) at cosmological scales in the tensor sector, based on the fact that GWs are direct distance tracers. Obtaining the redshift (whose knowledge is essential to test cosmology) is instead the challenge of GW cosmology. In absence of a direct electromagnetic counterpart to the GW event, the source goes under the name of ``dark siren'' and statistical techniques are used.
This talk aims at giving an overview of the state-of-the-art for these techniques as well as discussing perspectives for the future.
After introducing GW cosmology and statistical methods, I will present the latest measurements of the Hubble parameter and of the phenomenon of ``modified GW propagation'' (that takes place whenever GR is modified at cosmological scales), obtained from the latest Gravitational Wave Transient Catalog 3 with new, independent, open-source codes. In particular, the two techniques applied to real data so far consist in using the statistical correlation with galaxy catalogues and information from the mass distribution of Binary Black Holes.
I will discuss methodological aspects, relevant sources of systematics, the interplay with population studies, current challenges and possible ways forward.
I will finally present some not-yet-applied ideas for statistical dark siren techniques, in particular for third generation (3G) ground-based GW detectors.
Gravitational-wave (GW) cosmology provides a new way to measure the expansion history of the Universe and test General Relativity (GR) at cosmological scales in the tensor sector, based on the fact that GWs are direct distance tracers. Obtaining the redshift (whose knowledge is essential to test cosmology) is instead the challenge of GW cosmology. In absence of a direct electromagnetic counterpart to the GW event, the source goes under the name of ``dark siren'' and statistical techniques are used.
This talk aims at giving an overview of the state-of-the-art for these techniques as well as discussing perspectives for the future.
After introducing GW cosmology and statistical methods, I will present the latest measurements of the Hubble parameter and of the phenomenon of ``modified GW propagation'' (that takes place whenever GR is modified at cosmological scales), obtained from the latest Gravitational Wave Transient Catalog 3 with new, independent, open-source codes. In particular, the two techniques applied to real data so far consist in using the statistical correlation with galaxy catalogues and information from the mass distribution of Binary Black Holes.
I will discuss methodological aspects, relevant sources of systematics, the interplay with population studies, current challenges and possible ways forward.
I will finally present some not-yet-applied ideas for statistical dark siren techniques, in particular for third generation (3G) ground-based GW detectors.
Posted by: IC
Tue
5 Apr 2022
Charge and antipodal matching across spatial infinity
๐ London
Kevin Nguyen
(KCL)
Abstract:
Email m.godazgar@qmul.ac.uk for zoom link.
Abstract: I will present the derivation of the antipodal matching relations used to demonstrate the equivalence between soft graviton theorems and BMS charge conservation across spatial infinity. To this end I will provide a precise map between Bondi data at null infinity and Beig-Schmidt data at spatial infinity in a context appropriate to the gravitational scattering problem and celestial holography. I will also demonstrate that, among various proposals of BMS charges at null infinity found in the literature, only a subset match the conserved charges at spatial infinity and are therefore preferred from that perspective.
Email m.godazgar@qmul.ac.uk for zoom link.
Abstract: I will present the derivation of the antipodal matching relations used to demonstrate the equivalence between soft graviton theorems and BMS charge conservation across spatial infinity. To this end I will provide a precise map between Bondi data at null infinity and Beig-Schmidt data at spatial infinity in a context appropriate to the gravitational scattering problem and celestial holography. I will also demonstrate that, among various proposals of BMS charges at null infinity found in the literature, only a subset match the conserved charges at spatial infinity and are therefore preferred from that perspective.
Posted by: QMW
Mon
4 Apr 2022
A playful introudction to some modern geometry
Yang-Hui He
(LIMS and City)
Abstract:
With a view towards constructing Calabi Yau manifolds, we present some rudiments of the intersection between algebraic, differential and arithmetic geometry. Throughout we will take the opposite of the Bourbaki approach and work through explicit examples, rather than to emphasise on the theory.
With a view towards constructing Calabi Yau manifolds, we present some rudiments of the intersection between algebraic, differential and arithmetic geometry. Throughout we will take the opposite of the Bourbaki approach and work through explicit examples, rather than to emphasise on the theory.
Posted by: oxford
March 2022
Thu
31 Mar 2022
Numerical evidence for a Haagerup conformal field theory
Ying-Hsuan Lin
(Harvard)
Abstract:
We numerically study an anyon chain based on the Haagerup fusion category, and find evidence that it leads in the long-distance limit to a conformal field theory whose central charge is ~2; it will be possible to follow this talk online (please register at https://london-tqft.co.uk)
We numerically study an anyon chain based on the Haagerup fusion category, and find evidence that it leads in the long-distance limit to a conformal field theory whose central charge is ~2; it will be possible to follow this talk online (please register at https://london-tqft.co.uk)
Posted by: QMW
Thu
31 Mar 2022
Top Down Approach to Ensemble Averaging
๐ London
Jonathan Heckman
(University of Pennsylvania)
Abstract:
Ensemble averaging in quantum field theory is a well-defined procedure which is also of much recent interest in the context of the AdS/CFT correspondence. In this talk we present a stringy realization of quantum field theory ensembles in D \leq 4 spacetime dimensions. This provides a UV completion of a recent proposal of Marolf and Maxfield that there is a high-dimensional Hilbert space for baby universes, but one that is compatible with the proposed Swampland constraints of McNamara and Vafa. We identify two ways in which our construction breaks down, one of which is sensitive to short distance effects, and one which is an entropic effect for objects with a large number of microstates. The construction thus provides an explicit set of counterexamples to the claim that holography can be fully decoupled from top down considerations.
[for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
Ensemble averaging in quantum field theory is a well-defined procedure which is also of much recent interest in the context of the AdS/CFT correspondence. In this talk we present a stringy realization of quantum field theory ensembles in D \leq 4 spacetime dimensions. This provides a UV completion of a recent proposal of Marolf and Maxfield that there is a high-dimensional Hilbert space for baby universes, but one that is compatible with the proposed Swampland constraints of McNamara and Vafa. We identify two ways in which our construction breaks down, one of which is sensitive to short distance effects, and one which is an entropic effect for objects with a large number of microstates. The construction thus provides an explicit set of counterexamples to the claim that holography can be fully decoupled from top down considerations.
[for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Wed
30 Mar 2022
Singularity theorems in semiclassical gravity
๐ London
Eleni Kontou
(University of Amsterdam)
Abstract:
The classical singularity theorems predict the existence of singularities, defined using incomplete geodesics, under a set of general assumptions. One of those assumptions, namely the energy condition, is always violated by quantum fields and thus the realm of semiclassical gravity is outside the scope of these theorems. However, quantum fields do obey weaker conditions which can also be used to predict singularities. In this talk, I will present derivations of such semiclassical singularity theorems both in the timelike and the null case and discuss the challenges and open questions for each case.
The classical singularity theorems predict the existence of singularities, defined using incomplete geodesics, under a set of general assumptions. One of those assumptions, namely the energy condition, is always violated by quantum fields and thus the realm of semiclassical gravity is outside the scope of these theorems. However, quantum fields do obey weaker conditions which can also be used to predict singularities. In this talk, I will present derivations of such semiclassical singularity theorems both in the timelike and the null case and discuss the challenges and open questions for each case.
Posted by: andrea
Tue
29 Mar 2022
Multi-messenger cosmology: cross-correlating Stochastic Gravitational Wave Backgrounds and Cosmic Microwave Background
Angelo Ricciardon
(Padova University)
Abstract:
Gravitational Waves (GWs) have become one of the most powerful tools to explore our universe from its early epoch until nowadays, thanks to their freely propagating nature. After the GW detections from resolved sources by the LIGO/Virgo collaboration the next target of present and future ground and space-based interferometers is the detection of the stochastic background of GW (SGWB), both astrophysical or cosmological. General Relativity provides us with an extremely powerful and for free tool to extract astrophysical and cosmological information from the SGWB: the cross-correlation with other cosmological tracers, since their anisotropies share a common origin and the same perturbed geodesics. In this talk I will present some recent results about the study of the cross-correlation of the cosmological and astrophysical SGWBs with Cosmic Microwave Background (CMB) anisotropies, showing that future GW detectors, such as LISA or BBO, have the ability to measure such cross-correlation signals. I will also present a new tool in this context which can be used to reconstruct the expected SGWB maps starting from high resolution real Planck CMB maps.
Gravitational Waves (GWs) have become one of the most powerful tools to explore our universe from its early epoch until nowadays, thanks to their freely propagating nature. After the GW detections from resolved sources by the LIGO/Virgo collaboration the next target of present and future ground and space-based interferometers is the detection of the stochastic background of GW (SGWB), both astrophysical or cosmological. General Relativity provides us with an extremely powerful and for free tool to extract astrophysical and cosmological information from the SGWB: the cross-correlation with other cosmological tracers, since their anisotropies share a common origin and the same perturbed geodesics. In this talk I will present some recent results about the study of the cross-correlation of the cosmological and astrophysical SGWBs with Cosmic Microwave Background (CMB) anisotropies, showing that future GW detectors, such as LISA or BBO, have the ability to measure such cross-correlation signals. I will also present a new tool in this context which can be used to reconstruct the expected SGWB maps starting from high resolution real Planck CMB maps.
Posted by: IC
Tue
29 Mar 2022
Putting spin into black hole binaries
๐ London
Patricia Schmidt
(University of Birmingham)
Abstract:
Please email m.godazgar@qmul.ac.uk for zoom link.
Abstract: To date, gravitational waves from tens of merging stellar-mass black holes have been observed. These observations provide us with a
unique opportunity to probe the fundamental properties of astrophysical black holes. The precise measurement of the masses and spins
of black holes is particularly crucial to determine the evolutionary pathways of these binaries. This requires, however, highly accurate theoretical
models of the emitted gravitational-wave signal. The signal complexity grows with the number of degrees of freedom and the accurate modelling
general-relativistic spin-induced precession has proven to be challenging. In this talk, I will first discuss the current approaches to modelling
waveforms from precessing black hole binaries. I will then demonstrate the limitations and how they translate into systematic measurement uncertainties.
Please email m.godazgar@qmul.ac.uk for zoom link.
Abstract: To date, gravitational waves from tens of merging stellar-mass black holes have been observed. These observations provide us with a
unique opportunity to probe the fundamental properties of astrophysical black holes. The precise measurement of the masses and spins
of black holes is particularly crucial to determine the evolutionary pathways of these binaries. This requires, however, highly accurate theoretical
models of the emitted gravitational-wave signal. The signal complexity grows with the number of degrees of freedom and the accurate modelling
general-relativistic spin-induced precession has proven to be challenging. In this talk, I will first discuss the current approaches to modelling
waveforms from precessing black hole binaries. I will then demonstrate the limitations and how they translate into systematic measurement uncertainties.
Posted by: QMW
Mon
28 Mar 2022
LonTI: A Playful Introduction to Some Modern Geometry
Yang-Hui He
(LIMS and City)
Abstract:
With a view towards constructing Calabi Yau manifolds, we present some rudiments of the intersection between algebraic, differential and arithmetic geometry. Throughout we will take the opposite of the Bourbaki approach and work through explicit examples, rather than to emphasise on the theory.
With a view towards constructing Calabi Yau manifolds, we present some rudiments of the intersection between algebraic, differential and arithmetic geometry. Throughout we will take the opposite of the Bourbaki approach and work through explicit examples, rather than to emphasise on the theory.
Posted by: oxford
Mon
28 Mar 2022
Quantifying Intelligence Mathematically
Peter Cochrane
(University of Suffolk)
Abstract:
ABS:
TBC
NB: The colloquium will follow naturally on from the LonTI lecture and there will be refreshments.
BIO:
Professor Peter Cochrane, DSc, OBE, is Professor of Sentient Systems at the University of Suffolk, and visiting Professor to The University of Hertfordshire, Salford, and Nottingham Trent University has received numerous awards including the IEEE Millennium Medal, Martlesham Medal, Prince Philip Medal, Queens Award for Export and Technology and an OBE by The Queen in 1999.
He retired from BT as CTO in 2000 to form his own consultancy company. This saw the founding of eBookers, Shazam Entertainment, and a raft of smaller start ups. Peter has also seen assignments with UK, Singapore and Qatar government departments; HP, Motorola, 3M, Dupont, Ford, Sun, Apple, Cisco, Rolls Royce, BMW, Jersey Tel, Chorus, FaceBook, et al.
ABS:
TBC
NB: The colloquium will follow naturally on from the LonTI lecture and there will be refreshments.
BIO:
Professor Peter Cochrane, DSc, OBE, is Professor of Sentient Systems at the University of Suffolk, and visiting Professor to The University of Hertfordshire, Salford, and Nottingham Trent University has received numerous awards including the IEEE Millennium Medal, Martlesham Medal, Prince Philip Medal, Queens Award for Export and Technology and an OBE by The Queen in 1999.
He retired from BT as CTO in 2000 to form his own consultancy company. This saw the founding of eBookers, Shazam Entertainment, and a raft of smaller start ups. Peter has also seen assignments with UK, Singapore and Qatar government departments; HP, Motorola, 3M, Dupont, Ford, Sun, Apple, Cisco, Rolls Royce, BMW, Jersey Tel, Chorus, FaceBook, et al.
Posted by: oxford
Thu
24 Mar 2022
Liouville on the lattice
David Vegh
(QMUL)
Abstract:
The Liouville equation has many applications: it describes surfaces of constant negative curvature and plays an important role in non-critical string theory. In this talk we discuss how to put the Liouville equation on the lattice in a completely integrable way; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
The Liouville equation has many applications: it describes surfaces of constant negative curvature and plays an important role in non-critical string theory. In this talk we discuss how to put the Liouville equation on the lattice in a completely integrable way; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Posted by: QMW
Thu
24 Mar 2022
Symmetry theories and string theory
๐ London
Inaki Garcia-Etxebarria
(Durham)
Abstract:
M-theory on spaces with codimension 11-d singularities gives
rise to a rich class of d-dimensional field theories. I will discuss
how (d+1)-dimensional topological field theories (TFTs) encode the
higher symmetries and anomalies of these d-dimensional theories, and
how these TFTs can be extracted from the geometry of the singular
space. I will illustrate the discussion by analysing some simple
examples explicitly. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
M-theory on spaces with codimension 11-d singularities gives
rise to a rich class of d-dimensional field theories. I will discuss
how (d+1)-dimensional topological field theories (TFTs) encode the
higher symmetries and anomalies of these d-dimensional theories, and
how these TFTs can be extracted from the geometry of the singular
space. I will illustrate the discussion by analysing some simple
examples explicitly. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Wed
23 Mar 2022
Anomalies for anomalous symmetries.
๐ London
Avner Karasik
(Cambridge Univ. DAMTP)
Abstract:
4d gauge theories with massless fermions typically have axial U(1) transformations
that suffer from the ABJ anomaly. One can modify the theory of interest by adding
more fields in a way that restores the axial symmetry, and use it to derive rigorous
't-Hooft anomaly matching conditions. These conditions are not valid for the original
theory of interest, but for the modified theory. I will show that the modification can be
done in a specific way that allows us to relate the dynamics of the modified theory to
the dynamics of the original theory. In this way, the anomaly matching conditions of
the modified theory can be used to learn new things on the original theory even though
they involve axial transformations which are not a symmetry of the original theory.
In the talk I will describe this method and discuss some applications to various examples.
4d gauge theories with massless fermions typically have axial U(1) transformations
that suffer from the ABJ anomaly. One can modify the theory of interest by adding
more fields in a way that restores the axial symmetry, and use it to derive rigorous
't-Hooft anomaly matching conditions. These conditions are not valid for the original
theory of interest, but for the modified theory. I will show that the modification can be
done in a specific way that allows us to relate the dynamics of the modified theory to
the dynamics of the original theory. In this way, the anomaly matching conditions of
the modified theory can be used to learn new things on the original theory even though
they involve axial transformations which are not a symmetry of the original theory.
In the talk I will describe this method and discuss some applications to various examples.
Posted by: andrea
Tue
22 Mar 2022
On anomalies and gauging of U(1) non-invertible symmetries in 4d QED
๐ London
Avner Karasik
(Cambridge University)
Abstract:
I will present a way to promote the anomalous axial U(1) in 4d QED to an exact symmetry, with the price of losing its invertibility. I will then discuss some applications of this non-invertible U(1) symmetry. In particular, I will show how to couple this non-invertible symmetry to a gauge field. By taking this gauge field to be dynamical, we get a new type of gauge theory with unconventional interactions and constraints. By taking this gauge field to be background, we can study 't-Hooft anomalies of the non-invertible symmetry.
I will present a way to promote the anomalous axial U(1) in 4d QED to an exact symmetry, with the price of losing its invertibility. I will then discuss some applications of this non-invertible U(1) symmetry. In particular, I will show how to couple this non-invertible symmetry to a gauge field. By taking this gauge field to be dynamical, we get a new type of gauge theory with unconventional interactions and constraints. By taking this gauge field to be background, we can study 't-Hooft anomalies of the non-invertible symmetry.
Posted by: QMW
Tue
22 Mar 2022
The classical interior of black holes in holography
๐ London
Sean Hartnoll
(University of Cambridge)
Abstract:
(Email m.godazgar@qmul.ac.uk for zoom link)
Abstract: The exterior dynamics of black holes has played a major role
in holographic duality, describing the approach to thermal equilibrium
of strongly coupled media. The interior dynamics of black holes in a
holographic setting has, in contrast, been largely unexplored. I will
describe recent work investigating the classical interior dynamics of
various holographic black holes. I will discuss the nature of the
singularity, the absence of Cauchy horizons and a new kind of chaotic
behavior that emerges in the presence of charged scalar fields.
(Email m.godazgar@qmul.ac.uk for zoom link)
Abstract: The exterior dynamics of black holes has played a major role
in holographic duality, describing the approach to thermal equilibrium
of strongly coupled media. The interior dynamics of black holes in a
holographic setting has, in contrast, been largely unexplored. I will
describe recent work investigating the classical interior dynamics of
various holographic black holes. I will discuss the nature of the
singularity, the absence of Cauchy horizons and a new kind of chaotic
behavior that emerges in the presence of charged scalar fields.
Posted by: QMW
Mon
21 Mar 2022
LonTI: A Playful Introduction to Some Modern Geometry
Yang-Hui He
(LIMS and City)
Abstract:
With a view towards constructing Calabi Yau manifolds, we present some rudiments of the intersection between algebraic, differential and arithmetic geometry. Throughout we will take the opposite of the Bourbaki approach and work through explicit examples, rather than to emphasise on the theory.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
With a view towards constructing Calabi Yau manifolds, we present some rudiments of the intersection between algebraic, differential and arithmetic geometry. Throughout we will take the opposite of the Bourbaki approach and work through explicit examples, rather than to emphasise on the theory.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
Posted by: oxford
Thu
17 Mar 2022
A QFT for non-semisimple TQFT
Tudor Dimofte
(UC Davis and U. Edinburgh)
Abstract:
Topological twists of 3d N=4 gauge theories naturally give rise to non-semisimple 3d TQFT's. In mathematics, prototypical examples of the latter were constructed in the 90's (by Lyubashenko and others) from representation categories of small quantum groups at roots of unity; they were recently generalized in work of Costantino-Geer-Patureau Mirand and collaborators. I will introduce a family of physical 3d quantum field theories that (conjecturally) reproduce these classic non-semisimple TQFT's. The physical theories combine Chern-Simons-like and 3d N=4-like sectors. They are also related to Feigin-Tipunin vertex algebras, much the same way that Chern-Simons theory is related to WZW vertex algebras.
(Based on work with T. Creutzig, N. Garner, and N. Geer.); part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Topological twists of 3d N=4 gauge theories naturally give rise to non-semisimple 3d TQFT's. In mathematics, prototypical examples of the latter were constructed in the 90's (by Lyubashenko and others) from representation categories of small quantum groups at roots of unity; they were recently generalized in work of Costantino-Geer-Patureau Mirand and collaborators. I will introduce a family of physical 3d quantum field theories that (conjecturally) reproduce these classic non-semisimple TQFT's. The physical theories combine Chern-Simons-like and 3d N=4-like sectors. They are also related to Feigin-Tipunin vertex algebras, much the same way that Chern-Simons theory is related to WZW vertex algebras.
(Based on work with T. Creutzig, N. Garner, and N. Geer.); part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Posted by: QMW
Wed
16 Mar 2022
Entanglement in the quantum Hall matrix model
๐ London
Sean Hartnoll
(Cambridge Univ. DAMTP)
Abstract:
Quantum mechanical theories describing large N by N matrices of oscillators can lead to an emergent space as N -> infinity. In the most fully fledged version, the emergent space is dynamical and gravitating. However, there are also simpler, lower dimensional versions of this phenomenon. One of the simplest occurs in the so-called quantum Hall matrix model, in which a 2 dimensional space emerges and supports Chern-Simons dynamics. I will describe how this solvable model leads to insights about the emergence of space from matrices. In particular, I will describe how the emergent spatial locality is reflected in the entanglement structure of the ground state of theory.
Quantum mechanical theories describing large N by N matrices of oscillators can lead to an emergent space as N -> infinity. In the most fully fledged version, the emergent space is dynamical and gravitating. However, there are also simpler, lower dimensional versions of this phenomenon. One of the simplest occurs in the so-called quantum Hall matrix model, in which a 2 dimensional space emerges and supports Chern-Simons dynamics. I will describe how this solvable model leads to insights about the emergence of space from matrices. In particular, I will describe how the emergent spatial locality is reflected in the entanglement structure of the ground state of theory.
Posted by: andrea
Mon
14 Mar 2022
LonTI: On the SYK model and the Emergence of Spacetime
Damian Galante
(KCL)
Abstract:
In these lectures, we will present to seemingly different theories. The first one is a theory of gravity in two dimensions, called Jackiw-Teitelboim (JT) gravity, that is relevant in the context of higher-dimensional, near-extremal black holes. The second one is a quantum mechanical theory of fermions, with no gravity, called the Sachdev, Ye and Kitaev (SYK) model. We will explore precisely how JT gravity emerges from the SYK model by studying their actions, correlation functions and thermodynamic properties. This constitutes the simplest toy model of what theoretical physicists now call the holographic principle.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
In these lectures, we will present to seemingly different theories. The first one is a theory of gravity in two dimensions, called Jackiw-Teitelboim (JT) gravity, that is relevant in the context of higher-dimensional, near-extremal black holes. The second one is a quantum mechanical theory of fermions, with no gravity, called the Sachdev, Ye and Kitaev (SYK) model. We will explore precisely how JT gravity emerges from the SYK model by studying their actions, correlation functions and thermodynamic properties. This constitutes the simplest toy model of what theoretical physicists now call the holographic principle.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
Posted by: pethybridge
Thu
10 Mar 2022
Liouville conformal field theory: from probability theory to the conformal bootstrap
Vincent Vargas
(ENS, Paris)
Abstract:
Liouville conformal field theory (LCFT) was introduced by Polyakov in 1981 as an essential ingredient in his path integral construction of string theory. Since then Liouville theory has appeared in a wide variety of contexts ranging from random conformal geometry to 4d Yang-Mills theory with supersymmetry. Recently, a probabilistic construction of LCFT on general Riemann surfaces was provided using the 2d Gaussian Free Field. This construction can be seen as a rigorous construction of the 2d path integral introduced in Polyakov's 1981 work. In contrast to this construction, modern conformal field theory is based on representation theory and the so-called bootstrap procedure (based on recursive techniques) introduced in 1984 by Belavin-Polyakov-Zamolodchikov. In particular, a bootstrap construction for LCFT has been proposed in the mid 90's by Dorn-Otto-Zamolodchikov-Zamolodchikov (DOZZ) on the sphere. The aim of this talk is to review a recent series of work which shows the equivalence between the probabilistic construction and the bootstrap construction of LCFT on general Riemann surfaces. In particular, the equivalence is based on showing that LCFT satisfies a set of natural geometric axioms known as Segal's axioms; part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Liouville conformal field theory (LCFT) was introduced by Polyakov in 1981 as an essential ingredient in his path integral construction of string theory. Since then Liouville theory has appeared in a wide variety of contexts ranging from random conformal geometry to 4d Yang-Mills theory with supersymmetry. Recently, a probabilistic construction of LCFT on general Riemann surfaces was provided using the 2d Gaussian Free Field. This construction can be seen as a rigorous construction of the 2d path integral introduced in Polyakov's 1981 work. In contrast to this construction, modern conformal field theory is based on representation theory and the so-called bootstrap procedure (based on recursive techniques) introduced in 1984 by Belavin-Polyakov-Zamolodchikov. In particular, a bootstrap construction for LCFT has been proposed in the mid 90's by Dorn-Otto-Zamolodchikov-Zamolodchikov (DOZZ) on the sphere. The aim of this talk is to review a recent series of work which shows the equivalence between the probabilistic construction and the bootstrap construction of LCFT on general Riemann surfaces. In particular, the equivalence is based on showing that LCFT satisfies a set of natural geometric axioms known as Segal's axioms; part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Posted by: QMW
Thu
10 Mar 2022
A duality connecting neural network and cosmological dynamics
๐ London
Sven Krippendorf
(LMU Munich)
Abstract:
We demonstrate that the dynamics of neural networks trained with gradient descent and the dynamics of scalar fields in a flat, vacuum energy dominated Universe are structurally profoundly related. This duality provides the framework for synergies between these systems, to understand and explain neural network dynamics and new ways of simulating and describing early Universe models. Working in the continuous-time limit of neural networks, we analytically match the dynamics of the mean background and the dynamics of small perturbations around the mean field, highlighting potential differences in separate limits. We perform empirical tests of this analytic description and quantitatively show the dependence of the effective field theory parameters on hyperparameters of the neural network. As a result of this duality, the cosmological constant is matched inversely to the learning rate in the gradient descent update.
[for zoom link, please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
We demonstrate that the dynamics of neural networks trained with gradient descent and the dynamics of scalar fields in a flat, vacuum energy dominated Universe are structurally profoundly related. This duality provides the framework for synergies between these systems, to understand and explain neural network dynamics and new ways of simulating and describing early Universe models. Working in the continuous-time limit of neural networks, we analytically match the dynamics of the mean background and the dynamics of small perturbations around the mean field, highlighting potential differences in separate limits. We perform empirical tests of this analytic description and quantitatively show the dependence of the effective field theory parameters on hyperparameters of the neural network. As a result of this duality, the cosmological constant is matched inversely to the learning rate in the gradient descent update.
[for zoom link, please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
10 Mar 2022
Bootstrapping N = 4 super-Yang-Mills on the conformal manifold
Shai Chester
(Weizmann Institute)
Abstract:
We study the N = 4 SYM stress tensor multiplet 4-point function for any value of the complexified coupling tau, and in principle any gauge group (we focus on SU(2) and SU(3) for simplicity). By combining non-perturbative constraints from the numerical bootstrap with two exact constraints from supersymmetric localization, we are able to compute upper bounds on low-lying CFT data (e.g. the Konishi) for any value of tau. These upper bounds are very close to the 4-loop weak coupling predictions in the appropriate regime. We also give preliminary evidence that these upper bounds become small islands under reasonable assumptions, in which case our method would provide a numerical solution to N = 4 SYM for any gauge group and tau. –––– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant.
We study the N = 4 SYM stress tensor multiplet 4-point function for any value of the complexified coupling tau, and in principle any gauge group (we focus on SU(2) and SU(3) for simplicity). By combining non-perturbative constraints from the numerical bootstrap with two exact constraints from supersymmetric localization, we are able to compute upper bounds on low-lying CFT data (e.g. the Konishi) for any value of tau. These upper bounds are very close to the 4-loop weak coupling predictions in the appropriate regime. We also give preliminary evidence that these upper bounds become small islands under reasonable assumptions, in which case our method would provide a numerical solution to N = 4 SYM for any gauge group and tau. –––– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant.
Posted by: andrea
Wed
9 Mar 2022
Global structures from the infrared
๐ London
Michele Del Zotto
(Uppsala University)
Abstract:
Quantum field theories with identical local dynamics can admit different choices of global structure, leading to different partition functions and spectra of extended operators. Recent work has determined the structure of such choices via geometric methods for various classes of non-Lagrangian theories obtained from stringy geometric engineering techniques. In this talk I will discuss a purely field theoretical counterpart of this analysis, showing that global structures can be captured from a careful analysis of the infrared Coulomb-like phases. Our results confirm and extend the many results obtained within geometric engineering about the global structures of Argyres-Douglas theories, 5d SCFTs and 6d SCFTs.
Quantum field theories with identical local dynamics can admit different choices of global structure, leading to different partition functions and spectra of extended operators. Recent work has determined the structure of such choices via geometric methods for various classes of non-Lagrangian theories obtained from stringy geometric engineering techniques. In this talk I will discuss a purely field theoretical counterpart of this analysis, showing that global structures can be captured from a careful analysis of the infrared Coulomb-like phases. Our results confirm and extend the many results obtained within geometric engineering about the global structures of Argyres-Douglas theories, 5d SCFTs and 6d SCFTs.
Posted by: andrea
Tue
8 Mar 2022
Quantum gravity S-matrix Bootstrap
Andrea Guerrieri
(Tel-Aviv University)
Abstract:
In this talk I will review some of the recent developments in the S-matrix Bootstrap focussing on applications to effective field theories. As an example, I will apply the bootstrap methods to the supergravity effective field theory in ten dimensions.
I will show the improved numerical bootstrap bounds on the first correction to the universal graviton scattering and compare the result with the String Theory predictions. In the last part, I will comment on some new numerical ideas that will boost the explorations in different dimensions and for higher dimensional operators.
In this talk I will review some of the recent developments in the S-matrix Bootstrap focussing on applications to effective field theories. As an example, I will apply the bootstrap methods to the supergravity effective field theory in ten dimensions.
I will show the improved numerical bootstrap bounds on the first correction to the universal graviton scattering and compare the result with the String Theory predictions. In the last part, I will comment on some new numerical ideas that will boost the explorations in different dimensions and for higher dimensional operators.
Posted by: IC
Mon
7 Mar 2022
LonTI: On the SYK model and the Emergence of Spacetime
Damian Galante
(KCL)
Abstract:
In these lectures, we will present to seemingly different theories. The first one is a theory of gravity in two dimensions, called Jackiw-Teitelboim (JT) gravity, that is relevant in the context of higher-dimensional, near-extremal black holes. The second one is a quantum mechanical theory of fermions, with no gravity, called the Sachdev, Ye and Kitaev (SYK) model. We will explore precisely how JT gravity emerges from the SYK model by studying their actions, correlation functions and thermodynamic properties. This constitutes the simplest toy model of what theoretical physicists now call the holographic principle.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
In these lectures, we will present to seemingly different theories. The first one is a theory of gravity in two dimensions, called Jackiw-Teitelboim (JT) gravity, that is relevant in the context of higher-dimensional, near-extremal black holes. The second one is a quantum mechanical theory of fermions, with no gravity, called the Sachdev, Ye and Kitaev (SYK) model. We will explore precisely how JT gravity emerges from the SYK model by studying their actions, correlation functions and thermodynamic properties. This constitutes the simplest toy model of what theoretical physicists now call the holographic principle.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
Posted by: pethybridge
Thu
3 Mar 2022
Integrable scattering of massless particles and the AdS/CFT correspondence
๐ London
Alessandro Torrielli
(U. Surrey)
Abstract:
After a brief introduction to some of the impact which integrable methods and the Bethe ansatz have had on the study of the AdS/CFT correspondence in string theory, we will focus on the axiomatic approach to S-matrix theory in 1+1 dimensions. We will highlight the issues that arise when the particles are massless, and how this is in fact connected to Zamolodchikov's way of describing two-dimensional conformal field theories by means of integrability techniques. We will then mention how the axiomatic approach extends to form-factors, which are the gate to access the n-point functions of the theory. If time permits, we will briefly depict how this finds a contemporary application in the area of the AdS_3/CFT_2 correspondence; part of London TQFT Journal Club (please register at https://london-tqft.vercel.app);
After a brief introduction to some of the impact which integrable methods and the Bethe ansatz have had on the study of the AdS/CFT correspondence in string theory, we will focus on the axiomatic approach to S-matrix theory in 1+1 dimensions. We will highlight the issues that arise when the particles are massless, and how this is in fact connected to Zamolodchikov's way of describing two-dimensional conformal field theories by means of integrability techniques. We will then mention how the axiomatic approach extends to form-factors, which are the gate to access the n-point functions of the theory. If time permits, we will briefly depict how this finds a contemporary application in the area of the AdS_3/CFT_2 correspondence; part of London TQFT Journal Club (please register at https://london-tqft.vercel.app);
Posted by: QMW
Thu
3 Mar 2022
Homogeneous Yang-Baxter deformations as undeformed yet twisted models
Riccardo Borsato
(Santiago de Compostela U., IGFAE)
Abstract:
I will review recent progress in the study of a class of integrable deformations of sigma models known as "homogeneous Yang-Baxter". These deformations can be understood as generalisations of the well known TsT transformations. In fact, rather than deformations, the homogeneous Yang-Baxter procedure too can be reinterpreted as imposing twisted worldsheet boundary conditions in the undeformed sigma model. I will explain how to construct the twist in the generic case, which generalises the twist of TsT from abelian to non-abelian. I will also use the expression for the twist to discuss the construction of the classical spectral curve in some examples. To conclude, I will mention some open questions related to the quantum integrability of these models. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
I will review recent progress in the study of a class of integrable deformations of sigma models known as "homogeneous Yang-Baxter". These deformations can be understood as generalisations of the well known TsT transformations. In fact, rather than deformations, the homogeneous Yang-Baxter procedure too can be reinterpreted as imposing twisted worldsheet boundary conditions in the undeformed sigma model. I will explain how to construct the twist in the generic case, which generalises the twist of TsT from abelian to non-abelian. I will also use the expression for the twist to discuss the construction of the classical spectral curve in some examples. To conclude, I will mention some open questions related to the quantum integrability of these models. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Tue
1 Mar 2022
Classical general relativity from the double copy and the kinematic algebra of Yang-Mills theory
Gabriele Travaglini
(QMUL)
Abstract:
Scattering amplitudes of elementary particles exhibit a fascinating simplicity, which is entirely obscured in textbook Feynman-diagram computations. While these quantities find their primary application to collider physics, describing the dynamics of the tiniest particles in the universe, they also characterise the interactions among some of its heaviest objects, such as black holes. Violent collisions among black holes occur where tremendous amounts of energy are emitted, in the form of gravitational waves. 100 years after having been predicted by Einstein, their extraordinary direct detection in 2015 opened a fascinating window of observation of our universe at extreme energies never probed before, and it is now crucial to develop novel efficient methods for highly needed high-precision predictions. Thanks to their inherent simplicity, amplitudes are ideally suited to this task. I will begin by reviewing the computation of a very familiar quantity Newton's potential, from scattering amplitudes and unitarity. I will then explain how to compute directly observable quantities such as the scattering angle for light or for gravitons passing by a heavy mass such as a black hole. These computations are further simplified thanks to a remarkable, yet still mysterious connection between scattering amplitudes of gluons (in Yang-Mills theory) and those of gravitons (in Einstein's General relativity), known as the "double copy", whereby the latter amplitudes can be expressed, schematically, as sums of squares of the former – a property that cannot be possibly guessed by simply staring at the Lagrangians of the two theories. I will conclude by discussing the prospects of performing computations in Einstein gravity to higher orders in Newton's constant using a new, gauge-invariant version of the double copy, and as an example I will briefly discuss the computation of the scattering angle for classical black hole scattering to third post-Minkowskian order (or O(G^3) in Newton's constant G).
Scattering amplitudes of elementary particles exhibit a fascinating simplicity, which is entirely obscured in textbook Feynman-diagram computations. While these quantities find their primary application to collider physics, describing the dynamics of the tiniest particles in the universe, they also characterise the interactions among some of its heaviest objects, such as black holes. Violent collisions among black holes occur where tremendous amounts of energy are emitted, in the form of gravitational waves. 100 years after having been predicted by Einstein, their extraordinary direct detection in 2015 opened a fascinating window of observation of our universe at extreme energies never probed before, and it is now crucial to develop novel efficient methods for highly needed high-precision predictions. Thanks to their inherent simplicity, amplitudes are ideally suited to this task. I will begin by reviewing the computation of a very familiar quantity Newton's potential, from scattering amplitudes and unitarity. I will then explain how to compute directly observable quantities such as the scattering angle for light or for gravitons passing by a heavy mass such as a black hole. These computations are further simplified thanks to a remarkable, yet still mysterious connection between scattering amplitudes of gluons (in Yang-Mills theory) and those of gravitons (in Einstein's General relativity), known as the "double copy", whereby the latter amplitudes can be expressed, schematically, as sums of squares of the former – a property that cannot be possibly guessed by simply staring at the Lagrangians of the two theories. I will conclude by discussing the prospects of performing computations in Einstein gravity to higher orders in Newton's constant using a new, gauge-invariant version of the double copy, and as an example I will briefly discuss the computation of the scattering angle for classical black hole scattering to third post-Minkowskian order (or O(G^3) in Newton's constant G).
Posted by: IC
February 2022
Mon
28 Feb 2022
LonTI: On the SYK model and the Emergence of Spacetime
Damian Galante
(KCL)
Abstract:
In these lectures, we will present to seemingly different theories. The first one is a theory of gravity in two dimensions, called Jackiw-Teitelboim (JT) gravity, that is relevant in the context of higher-dimensional, near-extremal black holes. The second one is a quantum mechanical theory of fermions, with no gravity, called the Sachdev, Ye and Kitaev (SYK) model. We will explore precisely how JT gravity emerges from the SYK model by studying their actions, correlation functions and thermodynamic properties. This constitutes the simplest toy model of what theoretical physicists now call the holographic principle.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
In these lectures, we will present to seemingly different theories. The first one is a theory of gravity in two dimensions, called Jackiw-Teitelboim (JT) gravity, that is relevant in the context of higher-dimensional, near-extremal black holes. The second one is a quantum mechanical theory of fermions, with no gravity, called the Sachdev, Ye and Kitaev (SYK) model. We will explore precisely how JT gravity emerges from the SYK model by studying their actions, correlation functions and thermodynamic properties. This constitutes the simplest toy model of what theoretical physicists now call the holographic principle.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
Posted by: pethybridge
Thu
24 Feb 2022
Every conformal net has an associated VOA
Andre Henriques
(Oxford)
Abstract:
We show that every conformal net has an associated vertex algebra, thus identifying the class of conformal nets with a sub-class of the class of unitary vertex algebras. We also characterise those unitary vertex algebras that arise from a conformal net. (We conjecture that every unitary vertex algebras arises in this way, and hence that there is a bijective correspondence between conformal nets and unitary vertex algebras.) To construct the correspondence between conformal nets and unitary vertex algebras, we introduce a new notion of "field localised in a segment embedded in a Riemann surface", which could be of independent interest. This is joint work with James Tener; Part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
We show that every conformal net has an associated vertex algebra, thus identifying the class of conformal nets with a sub-class of the class of unitary vertex algebras. We also characterise those unitary vertex algebras that arise from a conformal net. (We conjecture that every unitary vertex algebras arises in this way, and hence that there is a bijective correspondence between conformal nets and unitary vertex algebras.) To construct the correspondence between conformal nets and unitary vertex algebras, we introduce a new notion of "field localised in a segment embedded in a Riemann surface", which could be of independent interest. This is joint work with James Tener; Part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Posted by: QMW
Thu
24 Feb 2022
Celestial OPE from twistor strings
๐ London
Eduardo Casali
(Harvard)
Abstract:
Celestial conformal field theory (CCFT) is a conjectured theory living on the celestial sphere of the asymptotic boundary of Minkowski. In analogy to the usual AdS/CFT dictionary, CCFTs would be dual to gravitational theories in the bulk, with bulk scattering amplitudes being dual to correlation functions on the celestial sphere. OPE coefficients are basic building blocks of CFTs which should also have an analogue in CCFTs. It has been shown that CCFT OPEs can be extracted from amplitudes with appropriate wavefunctions for external states, but there's still no direct computation using the CCFT itself since we lack a first principles definition. I will talk about recent work I have done computing these OPEs directly by using twistor strings, circumventing the issue of the target space theory. I will show how the worldsheet CFT of the twistor string gives a realization of the algebra of operators of the CCFT, reproducing the known leading OPE terms, as well as how it can be used to compute further regular terms in the OPE, beyond what is currently known. As a bonus, the worldsheet OPE also organizes the spectrum naturally in terms of the infinite dimensional symmetry algebras of CCFTs.
[for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
Celestial conformal field theory (CCFT) is a conjectured theory living on the celestial sphere of the asymptotic boundary of Minkowski. In analogy to the usual AdS/CFT dictionary, CCFTs would be dual to gravitational theories in the bulk, with bulk scattering amplitudes being dual to correlation functions on the celestial sphere. OPE coefficients are basic building blocks of CFTs which should also have an analogue in CCFTs. It has been shown that CCFT OPEs can be extracted from amplitudes with appropriate wavefunctions for external states, but there's still no direct computation using the CCFT itself since we lack a first principles definition. I will talk about recent work I have done computing these OPEs directly by using twistor strings, circumventing the issue of the target space theory. I will show how the worldsheet CFT of the twistor string gives a realization of the algebra of operators of the CCFT, reproducing the known leading OPE terms, as well as how it can be used to compute further regular terms in the OPE, beyond what is currently known. As a bonus, the worldsheet OPE also organizes the spectrum naturally in terms of the infinite dimensional symmetry algebras of CCFTs.
[for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
24 Feb 2022
Crosscap States in Integrable Theories
Joao Caetano
(CERN)
Abstract:
In this talk, I will describe crosscap states in integrable field theories and spin chains in 1+1 dimensions. I will derive an exact formula for overlaps between the crosscap state and any excited state in integrable field theories with diagonal scattering. I will then compute the crosscap entropy, i.e. the overlap for the ground state, in some examples. In the examples analyzed, the result turns out to decrease monotonically along the renormalization group flow except in cases where the discrete symmetry is spontaneously broken in the infrared. I will discuss crosscap states in integrable spin chains, and obtain determinant expressions for the overlaps with energy eigenstates. I will comment on the realization of crosscap states in holography. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
In this talk, I will describe crosscap states in integrable field theories and spin chains in 1+1 dimensions. I will derive an exact formula for overlaps between the crosscap state and any excited state in integrable field theories with diagonal scattering. I will then compute the crosscap entropy, i.e. the overlap for the ground state, in some examples. In the examples analyzed, the result turns out to decrease monotonically along the renormalization group flow except in cases where the discrete symmetry is spontaneously broken in the infrared. I will discuss crosscap states in integrable spin chains, and obtain determinant expressions for the overlaps with energy eigenstates. I will comment on the realization of crosscap states in holography. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
23 Feb 2022
Higher-Genus Partition Functions from Error-Correcting Codes
๐ London
Johan Henriksson
(Pisa University)
Abstract:
In this talk I will present some recent and ongoing work with Ashish Kakkar and Brian McPeak, where we describe a very explicit construction of a class of two-dimensional conformal field theories, denoted code CFTs. In the chiral case, code CFTs are constructed by compactifying n free bosons on a lattice, which in turn is defined from a classical error-correcting code via Construction A by Leech and Sloane. We show that constraints from higher-genus modular invariance on code CFTs can be recast into simple linear relations on the the higher-weight enumerator polynomial, which is a natural object from the code perspective. With this machinery at hand, we show that higher-genus modular invariance greatly reduces the number of seemingly consistent code CFT partition functions that were found by demanding modular invariance at genus one only. I will also cover some upcoming work, on the relation between quantum error-correcting codes and non-chiral (Narain) CFTs, and on averaging over code CFTs.
In this talk I will present some recent and ongoing work with Ashish Kakkar and Brian McPeak, where we describe a very explicit construction of a class of two-dimensional conformal field theories, denoted code CFTs. In the chiral case, code CFTs are constructed by compactifying n free bosons on a lattice, which in turn is defined from a classical error-correcting code via Construction A by Leech and Sloane. We show that constraints from higher-genus modular invariance on code CFTs can be recast into simple linear relations on the the higher-weight enumerator polynomial, which is a natural object from the code perspective. With this machinery at hand, we show that higher-genus modular invariance greatly reduces the number of seemingly consistent code CFT partition functions that were found by demanding modular invariance at genus one only. I will also cover some upcoming work, on the relation between quantum error-correcting codes and non-chiral (Narain) CFTs, and on averaging over code CFTs.
Posted by: andrea
Tue
22 Feb 2022
Almost Robinson geometry
Arman Taghavi-Chabert
(University of Warsaw)
Abstract:
Non-shearing congruences of null geodesics on four-dimensional Lorentzian manifolds are fundamental objects of mathematical relativity. Their prominence in exact solutions to the Einstein field equations is supported by major results such as the Robinson, Goldberg-Sachs and Kerr theorems. Conceptually, they lie at the crossroad between Lorentzian conformal geometry and Cauchy-Riemann geometry, and are one of the original ingredients of twistor theory. Identified as involutive totally null complex distributions of maximal rank, such congruences generalise to any even dimensions, under the name of Robinson structures. Nurowski and Trautman aptly described them as Lorentzian analogues of Hermitian structures. In this talk, I will give a survey of old and new results in the field.
Email m.godazgar@qmul.ac.uk for zoom link
Non-shearing congruences of null geodesics on four-dimensional Lorentzian manifolds are fundamental objects of mathematical relativity. Their prominence in exact solutions to the Einstein field equations is supported by major results such as the Robinson, Goldberg-Sachs and Kerr theorems. Conceptually, they lie at the crossroad between Lorentzian conformal geometry and Cauchy-Riemann geometry, and are one of the original ingredients of twistor theory. Identified as involutive totally null complex distributions of maximal rank, such congruences generalise to any even dimensions, under the name of Robinson structures. Nurowski and Trautman aptly described them as Lorentzian analogues of Hermitian structures. In this talk, I will give a survey of old and new results in the field.
Email m.godazgar@qmul.ac.uk for zoom link
Posted by: QMW
Mon
21 Feb 2022
LonTI: On the SYK model and the Emergence of Spacetime
Damian Galante
(KCL)
Abstract:
In these lectures, we will present to seemingly different theories. The first one is a theory of gravity in two dimensions, called Jackiw-Teitelboim (JT) gravity, that is relevant in the context of higher-dimensional, near-extremal black holes. The second one is a quantum mechanical theory of fermions, with no gravity, called the Sachdev, Ye and Kitaev (SYK) model. We will explore precisely how JT gravity emerges from the SYK model by studying their actions, correlation functions and thermodynamic properties. This constitutes the simplest toy model of what theoretical physicists now call the holographic principle.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
In these lectures, we will present to seemingly different theories. The first one is a theory of gravity in two dimensions, called Jackiw-Teitelboim (JT) gravity, that is relevant in the context of higher-dimensional, near-extremal black holes. The second one is a quantum mechanical theory of fermions, with no gravity, called the Sachdev, Ye and Kitaev (SYK) model. We will explore precisely how JT gravity emerges from the SYK model by studying their actions, correlation functions and thermodynamic properties. This constitutes the simplest toy model of what theoretical physicists now call the holographic principle.
Address: 21 Albemarle St, London W1S 4BS
Floor 2: London Institute of Mathematical Sciences (LIMS)
Posted by: pethybridge
Thu
17 Feb 2022
The quantum structure of the Standard Model effective field theory
๐ London
Mikael Chala
(Granada U.)
Abstract:
The Standard Model extended with non-renormalisable operators is increasingly becoming THE theory of the elementary particles and their interactions. A large part of current and future research is devoted to test this theory to the best possible accuracy. To this aim, though, substantial knowledge on its quantum structure is needed, both for theoretical reasons (constraints on the basis of relativity+quantum mechanics) and experimental ones (combine data gathered at very different energies). In this talk I will discuss the progress made over the years in this respect, with particular emphasis on major obstacles.
The Standard Model extended with non-renormalisable operators is increasingly becoming THE theory of the elementary particles and their interactions. A large part of current and future research is devoted to test this theory to the best possible accuracy. To this aim, though, substantial knowledge on its quantum structure is needed, both for theoretical reasons (constraints on the basis of relativity+quantum mechanics) and experimental ones (combine data gathered at very different energies). In this talk I will discuss the progress made over the years in this respect, with particular emphasis on major obstacles.
Posted by: QMW
Thu
17 Feb 2022
Applications of strong Szego limit theorem in AdS/CFT
Gregory Korchemsky
(IPhT Saclay)
Abstract:
I will review a recent progress in computing four-point correlation functions of infinitely heavy half-BPS operators in planar N = 4 SYM. Taking advantage of integrability of the theory, these correlation functions can be constructed in terms of fundamental building blocks - the octagon form factors. We show that the octagon form factor can be expressed as a Fredholm determinant of an integrable Bessel operator and demonstrate that this representation is very efficient in finding its dependence on the รขโฌโขt Hooft coupling and two cross ratios. At weak coupling, this yields a known series representation of the octagon in terms of ladder integrals. At strong coupling, we apply strong Szego limit theorem to develop a systematic expansion of the octagon in the inverse powers of the coupling constant and calculate accompanying expansion coefficients analytically. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
I will review a recent progress in computing four-point correlation functions of infinitely heavy half-BPS operators in planar N = 4 SYM. Taking advantage of integrability of the theory, these correlation functions can be constructed in terms of fundamental building blocks - the octagon form factors. We show that the octagon form factor can be expressed as a Fredholm determinant of an integrable Bessel operator and demonstrate that this representation is very efficient in finding its dependence on the รขโฌโขt Hooft coupling and two cross ratios. At weak coupling, this yields a known series representation of the octagon in terms of ladder integrals. At strong coupling, we apply strong Szego limit theorem to develop a systematic expansion of the octagon in the inverse powers of the coupling constant and calculate accompanying expansion coefficients analytically. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
16 Feb 2022
Old and new results on higher point correlation functions
๐ London
Vasco Goncalves
(University of Porto)
Abstract:
In this talk, I will review a duality between correlation function and null polygon Wilson loops and present this duality from a conformal bootstrap perspective.
In the process I will also work out, in detail, a new duality between spinning three point functions in large N conformal gauge theories and null polygonal hexagonal Wilson loop.
In this talk, I will review a duality between correlation function and null polygon Wilson loops and present this duality from a conformal bootstrap perspective.
In the process I will also work out, in detail, a new duality between spinning three point functions in large N conformal gauge theories and null polygonal hexagonal Wilson loop.
Posted by: andrea
Thu
10 Feb 2022
Random Matrix Theory and Quantum Chromodynamics–Recent Developments
Gernot Akemann
(U. Bielefeld)
Abstract:
The application of random matrix techniques in QCD and non-Abelian gauge theories in general has a long history e.g. in counting Feynman diagrams, going back to 't Hooft and others. In this talk I will focus on a different aspect that relates the two in the low energy spectrum of the QCD Dirac operator, as initiated by Shuryak and Verbaarschot. First, I will explain what is the approximation studied here where spectral statistics of random matrices apply, and where for example the technique of orthogonal polynomials can be useful in comparing to QCD lattice data. It is given by a particular finite volume low energy limit, the epsilon regime of chiral perturbation theory of Gasser and Leutwyler. I will mention how QCD parameters like quark masses, zero-modes, finite lattice spacing or chemical potential can be incorporated into the random matrix ensemble. In the last part I will discuss some recent work with my former student Tim Wurfel on the inclusion of finite temperature, that leads out of the standard classes of random matrices, but still remains analytically tractable. This talk is mainly based on the review arXiv:1603.06011 and the paper with Tim arXiv:2110.03617; part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
The application of random matrix techniques in QCD and non-Abelian gauge theories in general has a long history e.g. in counting Feynman diagrams, going back to 't Hooft and others. In this talk I will focus on a different aspect that relates the two in the low energy spectrum of the QCD Dirac operator, as initiated by Shuryak and Verbaarschot. First, I will explain what is the approximation studied here where spectral statistics of random matrices apply, and where for example the technique of orthogonal polynomials can be useful in comparing to QCD lattice data. It is given by a particular finite volume low energy limit, the epsilon regime of chiral perturbation theory of Gasser and Leutwyler. I will mention how QCD parameters like quark masses, zero-modes, finite lattice spacing or chemical potential can be incorporated into the random matrix ensemble. In the last part I will discuss some recent work with my former student Tim Wurfel on the inclusion of finite temperature, that leads out of the standard classes of random matrices, but still remains analytically tractable. This talk is mainly based on the review arXiv:1603.06011 and the paper with Tim arXiv:2110.03617; part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Posted by: QMW
Thu
10 Feb 2022
The geometry of effective field theories
๐ London
Laurentiu Rodina
(National Taiwan University)
Abstract:
I will describe the space of effective field theories consistent with local, unitary, and analytic UV completions, which was termed the EFThedron. Recently the EFThedron was generalized to a non-projective geometry, which can be used to implement new constraints on spectral functions. These include the unitarity bound, which leads to analytic bounds on single Wilson coefficients (instead of bounds only on ratios), or the low spin dominance condition, which drastically reduces the landscape of allowed theories. [for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
I will describe the space of effective field theories consistent with local, unitary, and analytic UV completions, which was termed the EFThedron. Recently the EFThedron was generalized to a non-projective geometry, which can be used to implement new constraints on spectral functions. These include the unitarity bound, which leads to analytic bounds on single Wilson coefficients (instead of bounds only on ratios), or the low spin dominance condition, which drastically reduces the landscape of allowed theories. [for zoom link please contact h(dot)jiang(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
10 Feb 2022
The spectral curve of segmented strings
David Vegh
(QMUL)
Abstract:
In this talk, I will discuss how to compute the spectral curve of "segmented strings" in AdS_3. The motion of a string in this target space is integrable and the worldsheet theory can be discretized while preserving integrability. The corresponding embeddings are segmented strings, which generalize piecewise linear strings in flat space. I will
present several examples. Next, I will introduce "brane tilings", which are doubly-periodic planar bipartite graphs. I will show that the motion of a closed segmented string can be embedded into the mutation dynamics of a certain brane tiling. This will enable us to compute the spectral curve by taking the determinant of the dressed adjacency matrix of the tiling. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
In this talk, I will discuss how to compute the spectral curve of "segmented strings" in AdS_3. The motion of a string in this target space is integrable and the worldsheet theory can be discretized while preserving integrability. The corresponding embeddings are segmented strings, which generalize piecewise linear strings in flat space. I will
present several examples. Next, I will introduce "brane tilings", which are doubly-periodic planar bipartite graphs. I will show that the motion of a closed segmented string can be embedded into the mutation dynamics of a certain brane tiling. This will enable us to compute the spectral curve by taking the determinant of the dressed adjacency matrix of the tiling. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
9 Feb 2022
DFT and alpha'-corrections
Linus Wulff
(Masaryk University)
Abstract:
I will argue that Double Field Theory (DFT) can describe some, but not all, alpha'-corrections to the tree-level string effective action. In particular, I will discuss how the first and second alpha'-corrections to the bosonic and heterotic string can be derived from DFT.
I will argue that Double Field Theory (DFT) can describe some, but not all, alpha'-corrections to the tree-level string effective action. In particular, I will discuss how the first and second alpha'-corrections to the bosonic and heterotic string can be derived from DFT.
Posted by: IC
Wed
9 Feb 2022
Kramers-Wannier-like duality defects in (3+1)d gauge theories
๐ London
Justin Kaidi
(Stony Brook U.)
Abstract:
I will introduce a class of non-invertible topological defects in (3+1)d gauge theories whose fusion rules are the higher-dimensional analogs of those of the Kramers-Wannier defect in the (1+1)d critical Ising model. As in the lower-dimensional case, the presence of such non-invertible defects implies self-duality under a particular gauging of the discrete (higher-form) symmetries. I will illustrate this by means of the example of SO(3) Yang-Mills (YM) at รยธ=รโฌ, as well as SU(2) N=4 SYM at รโ=i.
I will introduce a class of non-invertible topological defects in (3+1)d gauge theories whose fusion rules are the higher-dimensional analogs of those of the Kramers-Wannier defect in the (1+1)d critical Ising model. As in the lower-dimensional case, the presence of such non-invertible defects implies self-duality under a particular gauging of the discrete (higher-form) symmetries. I will illustrate this by means of the example of SO(3) Yang-Mills (YM) at รยธ=รโฌ, as well as SU(2) N=4 SYM at รโ=i.
Posted by: andrea
Tue
8 Feb 2022
A scale-critical trapped surface formation criterion for the Einstein-Maxwell system
Nikos Anathasiou
(American College of Thessaloniki)
Abstract:
Few notions within the realm of mathematical physics succeed in capturing the imagination and inspiring awe as well as that of a black hole. First encountered in the Schwarzschild solution, discovered a few months after the presentation of the Field Equations of General Relativity at the Prussian Academy of Sciences, the black hole as a mathematical phenomenon accompanies and prominently features within the history of General Relativity since its inception. In this talk we will lay out a brief history of the question of dynamical black hole formation in General Relativity and discuss a result, in collaboration with Xinliang An, on a scale-critical trapped surface formation criterion for the Einstein-Maxwell system.
Email m.godazgar@qmul.ac.uk for zoom link.
Few notions within the realm of mathematical physics succeed in capturing the imagination and inspiring awe as well as that of a black hole. First encountered in the Schwarzschild solution, discovered a few months after the presentation of the Field Equations of General Relativity at the Prussian Academy of Sciences, the black hole as a mathematical phenomenon accompanies and prominently features within the history of General Relativity since its inception. In this talk we will lay out a brief history of the question of dynamical black hole formation in General Relativity and discuss a result, in collaboration with Xinliang An, on a scale-critical trapped surface formation criterion for the Einstein-Maxwell system.
Email m.godazgar@qmul.ac.uk for zoom link.
Posted by: QMW
Tue
8 Feb 2022
Reviving chaotic inflation with fermion production: a supergravity model
Lorenzo Sorbo
(University of Massachusetts Amherst)
Abstract:
Processes of particle production during inflation can increase the amplitude of the scalar metric perturbations. We show that such a mechanism can naturally arise in supergravity models where an axion-like field drives large field inflation. In this class of models one generally expects instanton-like corrections to the superpotential. We show, by deriving the equations of motion in models of supergravity with a stabilizer, that such corrections generate an interaction between the inflaton and its superpartner. This inflaton-inflatino interaction term is rapidly oscillating, and can lead to copious production of inflatinos during inflation, filling the Fermi sphere up to momenta much larger than the Hubble parameter. In their turn, those fermions source inflaton fluctuations, increasing their amplitude, and effectively lowering the tensor-to-scalar ratio for the model. This allows, in particular, to bring the model where the inflaton potential is quadratic (plus negligibly small instanton corrections) to agree with all existing observations.
Processes of particle production during inflation can increase the amplitude of the scalar metric perturbations. We show that such a mechanism can naturally arise in supergravity models where an axion-like field drives large field inflation. In this class of models one generally expects instanton-like corrections to the superpotential. We show, by deriving the equations of motion in models of supergravity with a stabilizer, that such corrections generate an interaction between the inflaton and its superpartner. This inflaton-inflatino interaction term is rapidly oscillating, and can lead to copious production of inflatinos during inflation, filling the Fermi sphere up to momenta much larger than the Hubble parameter. In their turn, those fermions source inflaton fluctuations, increasing their amplitude, and effectively lowering the tensor-to-scalar ratio for the model. This allows, in particular, to bring the model where the inflaton potential is quadratic (plus negligibly small instanton corrections) to agree with all existing observations.
Posted by: IC
Thu
3 Feb 2022
Large N Factorization for Matrix Model Observables With Continuous and Discrete Symmetry
George Barnes
(QMUL)
Abstract:
Part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Posted by: QMW
Thu
3 Feb 2022
Jordan blocks and the Bethe ansatz: The eclectic spin chain as a limit
Juan Miguel Nieto Garcia
(University of Surrey)
Abstract:
In this talk, I will present a procedure to extract the generalised eigenvectors of a non-diagonalisable matrix by considering a diagonalisable perturbation of it and computing the non-diagonalisable limit of its eigenvectors. As an example, I will show how to compute a subset of the spectrum of the eclectic spin chain by computing the appropriate limit of the Bethe states of a twisted su(3) spin chain.
–––– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. Link emailed on Tuesday.
In this talk, I will present a procedure to extract the generalised eigenvectors of a non-diagonalisable matrix by considering a diagonalisable perturbation of it and computing the non-diagonalisable limit of its eigenvectors. As an example, I will show how to compute a subset of the spectrum of the eclectic spin chain by computing the appropriate limit of the Bethe states of a twisted su(3) spin chain.
–––– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. Link emailed on Tuesday.
Posted by: andrea
Wed
2 Feb 2022
1/4 BPS operators in N=4 Super Yang Mills
Agnese Bissi
(Uppsala)
Abstract:
I will discuss how to constrain four-point correlators involving at least one quarter BPS operator in N=4 Super Yang-Mills. I will present what can be learned by using crossing symmetry, chiral algebra, superspace techniques, and the structure of the operator product expansion. Finally, I will show how to make contact with the superconformal bootstrap program.
Contact your local Triangle organiser or Bogdan Stefanski for Zoom link.
I will discuss how to constrain four-point correlators involving at least one quarter BPS operator in N=4 Super Yang-Mills. I will present what can be learned by using crossing symmetry, chiral algebra, superspace techniques, and the structure of the operator product expansion. Finally, I will show how to make contact with the superconformal bootstrap program.
Contact your local Triangle organiser or Bogdan Stefanski for Zoom link.
Posted by: CityU2
Wed
2 Feb 2022
Gravitational Regge bounds
Alexander Zhiboedov
(CERN)
Abstract:
I will review the basic assumptions and spell out the detailed arguments that lead to the bound on the Regge growth of gravitational scattering amplitudes. The minimal extra ingredient compared to the gapped case - in addition to unitarity, analyticity, and crossing - that goes into the derivation is the assumption that scattering at large impact parameters is controlled by known semi-classical physics. I will also discuss bounds on the local growth of scattering amplitudes.
Contact your local Triangle organiser or Bogdan Stefanski for Zoom link.
I will review the basic assumptions and spell out the detailed arguments that lead to the bound on the Regge growth of gravitational scattering amplitudes. The minimal extra ingredient compared to the gapped case - in addition to unitarity, analyticity, and crossing - that goes into the derivation is the assumption that scattering at large impact parameters is controlled by known semi-classical physics. I will also discuss bounds on the local growth of scattering amplitudes.
Contact your local Triangle organiser or Bogdan Stefanski for Zoom link.
Posted by: CityU2
Tue
1 Feb 2022
Stabilising relativistic fluids on slowly expanding cosmological spacetimes
Zoe Wyatt
(King's College London)
Abstract:
On a background Minkowski spacetime, the relativistic Euler equations are known, for a relatively general equation of state, to admit unstable homogeneous solutions with finite-time shock formation. By contrast, such shock formation can be suppressed on background cosmological spacetimes whose spatial slices expand at an accelerated rate. The critical case of linear, ie zero-accelerated, spatial expansion, is not as well understood. In this talk, I will present two recent works concerning the relativistic Euler and the Einstein-Dust equations for geometries expanding at a linear rate. This is based on joint works with David Fajman, Todd Oliynyk and Max Ofner.
Email m.godazgar@qmul.ac.uk for zoom link
On a background Minkowski spacetime, the relativistic Euler equations are known, for a relatively general equation of state, to admit unstable homogeneous solutions with finite-time shock formation. By contrast, such shock formation can be suppressed on background cosmological spacetimes whose spatial slices expand at an accelerated rate. The critical case of linear, ie zero-accelerated, spatial expansion, is not as well understood. In this talk, I will present two recent works concerning the relativistic Euler and the Einstein-Dust equations for geometries expanding at a linear rate. This is based on joint works with David Fajman, Todd Oliynyk and Max Ofner.
Email m.godazgar@qmul.ac.uk for zoom link
Posted by: QMW
Tue
1 Feb 2022
Small Cosmological Constants in String Theory
Liam McAllister
(Cornell University)
Abstract:
We construct vacua of string theory in which all moduli are stabilized and the magnitude of the cosmological constant is exponentially small. The vacua are supersymmetric AdS4 solutions in flux compactifications of type IIB string theory on orientifolds of Calabi-Yau hypersurfaces. I will explain the advances in computing topological data in Calabi-Yau compactifications that led to these solutions, then speculate about implications for the cosmological constant problem. The vacuum energy is small because we ensure the exact cancellation of all perturbative contributions, through an explicit choice of integer parameters determined by the topology and quantized fluxes. The nonperturbative contributions that remain are exponential in these integers. Finding cosmological constants of small magnitude in this landscape is exponentially easier than in Bousso-Polchinski landscapes. Extending this approach to positive cosmological constants in realistic universes is a difficult open problem.
We construct vacua of string theory in which all moduli are stabilized and the magnitude of the cosmological constant is exponentially small. The vacua are supersymmetric AdS4 solutions in flux compactifications of type IIB string theory on orientifolds of Calabi-Yau hypersurfaces. I will explain the advances in computing topological data in Calabi-Yau compactifications that led to these solutions, then speculate about implications for the cosmological constant problem. The vacuum energy is small because we ensure the exact cancellation of all perturbative contributions, through an explicit choice of integer parameters determined by the topology and quantized fluxes. The nonperturbative contributions that remain are exponential in these integers. Finding cosmological constants of small magnitude in this landscape is exponentially easier than in Bousso-Polchinski landscapes. Extending this approach to positive cosmological constants in realistic universes is a difficult open problem.
Posted by: IC
January 2022
Thu
27 Jan 2022
Schur-Weyl Duality, Diagram Algebras and Matrix Observables
Adrian Padellaro
(QMUL)
Abstract:
TBA; part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
TBA; part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Posted by: QMW
Thu
27 Jan 2022
Effective Field Theory of Chaotic Spectral Correlations
Brian Swingle
(Maryland U.)
Abstract:
Ensembles of quantum chaotic systems are expected to exhibit random matrix universality in their energy spectrum. The presence of this universality can be diagnosed by looking for a linear in time 'ramp' in the spectral form factor, but for realistic systems this feature is typically only visible after a sufficiently long time. Given the wide prevalence of this random matrix behavior, it is natural to ask for an effective field theory which predicts the ramp and computes corrections to it arising from physical constraints. I will present such an effective theory based on fluctuating hydrodynamics. The theory can also be adapted to describe the effects of spontaneous symmetry breaking on spectral correlations. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Ensembles of quantum chaotic systems are expected to exhibit random matrix universality in their energy spectrum. The presence of this universality can be diagnosed by looking for a linear in time 'ramp' in the spectral form factor, but for realistic systems this feature is typically only visible after a sufficiently long time. Given the wide prevalence of this random matrix behavior, it is natural to ask for an effective field theory which predicts the ramp and computes corrections to it arising from physical constraints. I will present such an effective theory based on fluctuating hydrodynamics. The theory can also be adapted to describe the effects of spontaneous symmetry breaking on spectral correlations. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
27 Jan 2022
Wilson loop in general representation and RG flow in 1d defect QFT
Arkady Tseytlin
(Imperial College London)
Abstract:
The generalized Wilson loop operator interpolating between the
supersymmetric and the ordinary Wilson loop in \(\mathcal{N}\)=4 SYM theory provides an interesting example of renormalization group flow on a line defect: the scalar coupling parameter \(\zeta\) has a non-trivial beta function and may be viewed as a running
coupling constant in a 1d defect QFT.
We continue the study of this operator, generalizing previous results for the beta function and Wilson loop expectation
value to the case of an arbitrary representation of the gauge group and away from the planar limit.
Focusing on the scalar ladder limit where the generalized Wilson loop reduces to a purely scalar line operator in a free adjoint theory, and specializing to the case
of the rank \(k\) symmetric representation of \(SU(N)\), we also study a certain "semiclassical"
limit where \(k\) is taken to infinity with \(k \zeta^2\) fixed. This limit can be conveniently studied using a 1d defect QFT representation in terms of path integral over
\(N\) commuting 1d bosons. Using this representation, we compute the beta function and circular loop expectation
value in the large \(k\) limit, and use it to derive constraints on the structure of the beta function for general
representation. We discuss the corresponding 1d RG flow and comment on the consistency of the results with
the 1d defect version of the F-theorem. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
The generalized Wilson loop operator interpolating between the
supersymmetric and the ordinary Wilson loop in \(\mathcal{N}\)=4 SYM theory provides an interesting example of renormalization group flow on a line defect: the scalar coupling parameter \(\zeta\) has a non-trivial beta function and may be viewed as a running
coupling constant in a 1d defect QFT.
We continue the study of this operator, generalizing previous results for the beta function and Wilson loop expectation
value to the case of an arbitrary representation of the gauge group and away from the planar limit.
Focusing on the scalar ladder limit where the generalized Wilson loop reduces to a purely scalar line operator in a free adjoint theory, and specializing to the case
of the rank \(k\) symmetric representation of \(SU(N)\), we also study a certain "semiclassical"
limit where \(k\) is taken to infinity with \(k \zeta^2\) fixed. This limit can be conveniently studied using a 1d defect QFT representation in terms of path integral over
\(N\) commuting 1d bosons. Using this representation, we compute the beta function and circular loop expectation
value in the large \(k\) limit, and use it to derive constraints on the structure of the beta function for general
representation. We discuss the corresponding 1d RG flow and comment on the consistency of the results with
the 1d defect version of the F-theorem. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
26 Jan 2022
Multi-loop scattering amplitudes and gravitational binary dynamics
๐ London
Mao Zeng
(University of Edinburgh)
Abstract:
Next-generation gravitational wave detectors require highly precise predictions for the waveforms from inspiraling black holes and neutron stars. We present advances in binary inspiral dynamics by taking classical limits of scattering amplitudes in perturbative quantum gravity. The amplitudes are calculated efficiently using modern methods for scattering amplitudes, including double copy and generalized unitarity, and loop integration techniques borrowed from collider physics. Classical physics can be extracted by several complementary approaches, including effective field theory, eikonal exponentiation, and observables in wavepacket scattering. For both conservative and dissipative dynamics of binary systems, we obtain new terms in the post-Minksowskian expansion beyond the best previous results from purely classical methods.
Next-generation gravitational wave detectors require highly precise predictions for the waveforms from inspiraling black holes and neutron stars. We present advances in binary inspiral dynamics by taking classical limits of scattering amplitudes in perturbative quantum gravity. The amplitudes are calculated efficiently using modern methods for scattering amplitudes, including double copy and generalized unitarity, and loop integration techniques borrowed from collider physics. Classical physics can be extracted by several complementary approaches, including effective field theory, eikonal exponentiation, and observables in wavepacket scattering. For both conservative and dissipative dynamics of binary systems, we obtain new terms in the post-Minksowskian expansion beyond the best previous results from purely classical methods.
Posted by: andrea
Wed
26 Jan 2022
4d N=2 supergravity observables from Nekrasov-like partition functions
Kiril Hristov
(Sofia University)
Abstract:
We reinterpret the OSV formula for the on-shell action/entropy function of asymptotically flat BPS black holes as a fixed point formula that is formally equivalent to a recent gluing proposal for asymptotically AdS4 black holes. This prompts a conjecture that the complete perturbative answer for the most general gravitational building block of 4d N=2 supergravity at a single fixed point takes the form of a Nekrasov-like partition function with equivariant parameters related to the higher-derivative expansion of the prepotential. In turn this leads to a simple localization-like proposal for a set of supersymmetric partition functions in (UV completed) 4d N=2 supergravity theories. The conjecture is shown to be in agreement with a number of available results for different BPS backgrounds with both Minkowski and AdS asymptotics. In particular, it follows that the OSV formula comes from the unrefined limit of the general expression including only the so-called W tower of higher derivatives, while the on-shell action of pure (Euclidean) AdS4 with round S3 boundary comes from the NS limit that includes only the T tower.
We reinterpret the OSV formula for the on-shell action/entropy function of asymptotically flat BPS black holes as a fixed point formula that is formally equivalent to a recent gluing proposal for asymptotically AdS4 black holes. This prompts a conjecture that the complete perturbative answer for the most general gravitational building block of 4d N=2 supergravity at a single fixed point takes the form of a Nekrasov-like partition function with equivariant parameters related to the higher-derivative expansion of the prepotential. In turn this leads to a simple localization-like proposal for a set of supersymmetric partition functions in (UV completed) 4d N=2 supergravity theories. The conjecture is shown to be in agreement with a number of available results for different BPS backgrounds with both Minkowski and AdS asymptotics. In particular, it follows that the OSV formula comes from the unrefined limit of the general expression including only the so-called W tower of higher derivatives, while the on-shell action of pure (Euclidean) AdS4 with round S3 boundary comes from the NS limit that includes only the T tower.
Posted by: IC
Tue
25 Jan 2022
Is the Hubble constant a constant?
Eoin Colgain
(Sogang University)
Abstract:
In recent years Adam Riess' SH0ES collaboration has made it fashionable to question Lambda-CDM through a series of steadily more precise local determinations of the Hubble constant, the latest of which currently stands at H0 = 73 รยฑ 1 km/s/Mpc. On the other hand, questioning the FLRW paradigm is still taboo. However, if there is a 5 sigma discrepancy with Planck, then a good explanation is required. In the talk, I will explain why H0 should be bounded above by H0 ~ 71 km/s/Mpc in any FLRW cosmology, before presenting some observations that appear to challenge the working FLRW assumption that the Universe is isotropic and homogeneous. Time permitting, I will spell out the implications of a higher local H0 for dark energy models.
In recent years Adam Riess' SH0ES collaboration has made it fashionable to question Lambda-CDM through a series of steadily more precise local determinations of the Hubble constant, the latest of which currently stands at H0 = 73 รยฑ 1 km/s/Mpc. On the other hand, questioning the FLRW paradigm is still taboo. However, if there is a 5 sigma discrepancy with Planck, then a good explanation is required. In the talk, I will explain why H0 should be bounded above by H0 ~ 71 km/s/Mpc in any FLRW cosmology, before presenting some observations that appear to challenge the working FLRW assumption that the Universe is isotropic and homogeneous. Time permitting, I will spell out the implications of a higher local H0 for dark energy models.
Posted by: IC
Thu
20 Jan 2022
Relative Defects and Trapped Higher-Form Symmetries
Lakshya Bhardwaj
(Oxford)
Abstract:
Relative theories are non-topological theories living at the boundaries of TQFTs in one higher dimension. An interesting and well-studied class of relative theories are 6d N=(2,0) theories. I will introduce the notion of relative defects in relative theories, which are non-topological defects of the relative theory living at the boundary of a topological defect of the above-mentioned TQFT in one higher dimension. I will argue that codimension two defects of 6d N=(2,0) theories are relative defects. Relative defects carry ''trapped'' higher-form symmetries localized on their world-volume which are independent from the higher-form symmetries of the bulk theory. When the bulk theory is compactified with the insertion of relative defects, the trapped higher-form symmetries provide extra contributions to the higher-form symmetries of the lower-dimensional theory resulting from the compactification. For example, when 6d N=(2,0) theories are compactified on a Riemann surfaces with punctures (which are relative codimension-two defects) then the 1-form symmetry of the resulting 4d N=2 Class S theory obtains contributions from the 1-form symmetries trapped at the punctures, along with the well-known contribution coming from the 2-form symmetry of the 6d N=(2,0) theory; part of London TQFT Journal Club; it will be possible to follow this talk on Zoom (please register at https://london-tqft.vercel.app)
Relative theories are non-topological theories living at the boundaries of TQFTs in one higher dimension. An interesting and well-studied class of relative theories are 6d N=(2,0) theories. I will introduce the notion of relative defects in relative theories, which are non-topological defects of the relative theory living at the boundary of a topological defect of the above-mentioned TQFT in one higher dimension. I will argue that codimension two defects of 6d N=(2,0) theories are relative defects. Relative defects carry ''trapped'' higher-form symmetries localized on their world-volume which are independent from the higher-form symmetries of the bulk theory. When the bulk theory is compactified with the insertion of relative defects, the trapped higher-form symmetries provide extra contributions to the higher-form symmetries of the lower-dimensional theory resulting from the compactification. For example, when 6d N=(2,0) theories are compactified on a Riemann surfaces with punctures (which are relative codimension-two defects) then the 1-form symmetry of the resulting 4d N=2 Class S theory obtains contributions from the 1-form symmetries trapped at the punctures, along with the well-known contribution coming from the 2-form symmetry of the 6d N=(2,0) theory; part of London TQFT Journal Club; it will be possible to follow this talk on Zoom (please register at https://london-tqft.vercel.app)
Posted by: QMW
Wed
19 Jan 2022
Infrared phases of 2d QCD
๐ London
Diego Delmastro
(Perimeter Institute)
Abstract:
We will study some aspects of Quantum Chromodynamics (QCD) in d=1+1 spacetime dimensions. The theory presents many of the same challenges as d=3+1 dimensional QCD (e.g., strong interactions where perturbation theory breaks down, chiral quarks which are hard to put on the lattice, etc.). But, in 2d, there are also some special features that make the problem more tractable. We will see that one can effectively solve the system at strong coupling, revealing interesting connections to other well-studied theories such as 2d rational CFTs (minimal models, WZW models, etc.).
We will study some aspects of Quantum Chromodynamics (QCD) in d=1+1 spacetime dimensions. The theory presents many of the same challenges as d=3+1 dimensional QCD (e.g., strong interactions where perturbation theory breaks down, chiral quarks which are hard to put on the lattice, etc.). But, in 2d, there are also some special features that make the problem more tractable. We will see that one can effectively solve the system at strong coupling, revealing interesting connections to other well-studied theories such as 2d rational CFTs (minimal models, WZW models, etc.).
Posted by: andrea
Wed
19 Jan 2022
The limitations of the holographic idea
Samir Mathur
(Ohio State University)
Abstract:
The black hole information paradox has been tightened to a precise contradiction by the small corrections theorem. Resolving the puzzle thus needs an order unity correction to semiclassical dynamics at the horizon. Remarkably, in string theory we find that microstates of black holes are `fuzzballs' with no horizon, which resolves the paradox. An alternative to the fuzzball paradigm is has been sought through a `wormhole paradigm' where the horizon would be continue to be described by semiclassical physics on a code subspace of the full quantum degrees of freedom. This wormhole paradigm can however can be ruled out by an extension of the small corrections theorem. We argue that the notions of ER=EPR etc underlying the wormhole paradigm are incorrect, and that the error arises from using the eternal spacetime geometry which is itself inconsistent with the requirements of unitarity.
The black hole information paradox has been tightened to a precise contradiction by the small corrections theorem. Resolving the puzzle thus needs an order unity correction to semiclassical dynamics at the horizon. Remarkably, in string theory we find that microstates of black holes are `fuzzballs' with no horizon, which resolves the paradox. An alternative to the fuzzball paradigm is has been sought through a `wormhole paradigm' where the horizon would be continue to be described by semiclassical physics on a code subspace of the full quantum degrees of freedom. This wormhole paradigm can however can be ruled out by an extension of the small corrections theorem. We argue that the notions of ER=EPR etc underlying the wormhole paradigm are incorrect, and that the error arises from using the eternal spacetime geometry which is itself inconsistent with the requirements of unitarity.
Posted by: IC
Thu
13 Jan 2022
TQFTs from SCFTs in 3D
Hongliang Jiang
(QMUL)
Abstract:
I will discuss the paper https://arxiv.org/abs/2103.09283, where 3D non-unitary TQFTs are obtained from 3D N=4 rank 0 SCFTs; It will be possible to follow this talk on Zoom (please visit https://london-tqft.vercel.app to register).
I will discuss the paper https://arxiv.org/abs/2103.09283, where 3D non-unitary TQFTs are obtained from 3D N=4 rank 0 SCFTs; It will be possible to follow this talk on Zoom (please visit https://london-tqft.vercel.app to register).
Posted by: QMW
Thu
6 Jan 2022
Journal Club on Non-Invertible Duality Defects in 3+1 Dimensions
Rajath Radhakrishnan
(QMUL)
Abstract:
Discussion of https://arxiv.org/pdf/2111.01139.pdf and https://arxiv.org/pdf/2111.01141.pdf. Part of new "London TQFT Journal Club" series at QMUL, please visit https://london-tqft.vercel.app to register for this and future events; some of these future meetings will be more like standard talks with speakers discussing their own work, while some will be–like this meeting–a more traditional journal club event. (Now on Zoom instead!)
Discussion of https://arxiv.org/pdf/2111.01139.pdf and https://arxiv.org/pdf/2111.01141.pdf. Part of new "London TQFT Journal Club" series at QMUL, please visit https://london-tqft.vercel.app to register for this and future events; some of these future meetings will be more like standard talks with speakers discussing their own work, while some will be–like this meeting–a more traditional journal club event. (Now on Zoom instead!)
Posted by: QMW
Mon
3 Jan 2022
String (In)Stability Issues with Broken Supersymmetry
Augusto Sagnotti
(Scuola Normale Superiore and INFN)
Abstract:
I shall review some key features of the three ten-dimensional string models with broken supersymmetry that are free of tachyonic modes. Their leading back-reactions are runaway รขโฌลtadpole potentialsรขโฌย, which have important effects on their ambient spacetimes. When these are explored in detail within the low-energy effective theory, some surprising features emerge:
รยทTadpole potentials can drive interesting spontaneous compactifications;
รยทIn Cosmology, they can lead to the peculiar รขโฌลclimbing scenarioรขโฌย for fast-to-slow-roll transitions.
Puzzling instabilities typically accompany broken supersymmetry in String Theory. However, they are absent in the former setting, and point to a mere breakdown of isotropy in the latter, which resonates with the very emergence of compact dimensions. I shall address these issues, trying to emphasize potential lessons and some key open questions.
I shall review some key features of the three ten-dimensional string models with broken supersymmetry that are free of tachyonic modes. Their leading back-reactions are runaway รขโฌลtadpole potentialsรขโฌย, which have important effects on their ambient spacetimes. When these are explored in detail within the low-energy effective theory, some surprising features emerge:
รยทTadpole potentials can drive interesting spontaneous compactifications;
รยทIn Cosmology, they can lead to the peculiar รขโฌลclimbing scenarioรขโฌย for fast-to-slow-roll transitions.
Puzzling instabilities typically accompany broken supersymmetry in String Theory. However, they are absent in the former setting, and point to a mere breakdown of isotropy in the latter, which resonates with the very emergence of compact dimensions. I shall address these issues, trying to emphasize potential lessons and some key open questions.
Posted by: IC