Triangle Seminars
December 2022
Wed
14 Dec 2022
Bootstrapping the 6D (2,0) theory with Reinforcement Learning
๐ London
Costis Papageorgakis
(QMUL)
Abstract:
I will describe a method for approximately solving the crossing equations in a general CFT, using Reinforcement Learning as a stochastic optimiser. I will then present an application of this approach in the context of the 6D (2,0) theory
I will describe a method for approximately solving the crossing equations in a general CFT, using Reinforcement Learning as a stochastic optimiser. I will then present an application of this approach in the context of the 6D (2,0) theory
Posted by: andrea
Mon
12 Dec 2022
AdS Virasoro-Shapiro from single-valued periods
Luis Fernando Alday
(University of Oxford)
Abstract:
We determine the full 1/sqrt(lambda) correction to the flat-space Wilson coefficients which enter the AdS Virasoro-Shapiro amplitude in N=4 SYM theory at strong coupling. The assumption that the Wilson coefficients are in the ring of single-valued multiple zeta values, as expected for closed string amplitudes, is surprisingly powerful and leads to a unique solution to the dispersive sum rules relating Wilson coefficients and OPE data. The corresponding OPE data fully agrees with and extends the results from integrability.
We determine the full 1/sqrt(lambda) correction to the flat-space Wilson coefficients which enter the AdS Virasoro-Shapiro amplitude in N=4 SYM theory at strong coupling. The assumption that the Wilson coefficients are in the ring of single-valued multiple zeta values, as expected for closed string amplitudes, is surprisingly powerful and leads to a unique solution to the dispersive sum rules relating Wilson coefficients and OPE data. The corresponding OPE data fully agrees with and extends the results from integrability.
Posted by: IC2
Wed
7 Dec 2022
Quantum theory of classical turbulence: part 2
Alexander Migdal
(NYU)
Abstract:
A new approach to strong turbulence based on ideas of dynamical geometry and topological conservation laws is developed.
In terms of the quantum field theory, this is another example of the duality between a fluctuating vector field and fluctuating geometry.
Some new exact solutions of Navier-Stokes and Euler equations are found. The loop equation suggested in the early 90-ties is investigated in detail.
The loop equation plays the same role in our theory as the Boltzmann kinetic equation in statistical physics.
It has the form of the Schrรยถdinger equation with a complex Hamiltonian in loop space. The viscosity plays the role of Planck's constant.
Strong turbulence corresponds to the WKB limit of the loop equation.
In this limit, we find a fixed point of the loop equation we call Kelvinon.
Kelvinon has a conserved circulation for a fixed loop in space, generalizing Kelvin's theorem.
Clebsch field of this solution has nontrivial topology with two winding numbers.
These topological conservation laws allow us to compute the PDF of circulation in a WKB limit (large circulation in the viscosity units).
This PDF perfectly matches the results of numerical simulations of the conventional forced Navier-Stokes equation.
A new approach to strong turbulence based on ideas of dynamical geometry and topological conservation laws is developed.
In terms of the quantum field theory, this is another example of the duality between a fluctuating vector field and fluctuating geometry.
Some new exact solutions of Navier-Stokes and Euler equations are found. The loop equation suggested in the early 90-ties is investigated in detail.
The loop equation plays the same role in our theory as the Boltzmann kinetic equation in statistical physics.
It has the form of the Schrรยถdinger equation with a complex Hamiltonian in loop space. The viscosity plays the role of Planck's constant.
Strong turbulence corresponds to the WKB limit of the loop equation.
In this limit, we find a fixed point of the loop equation we call Kelvinon.
Kelvinon has a conserved circulation for a fixed loop in space, generalizing Kelvin's theorem.
Clebsch field of this solution has nontrivial topology with two winding numbers.
These topological conservation laws allow us to compute the PDF of circulation in a WKB limit (large circulation in the viscosity units).
This PDF perfectly matches the results of numerical simulations of the conventional forced Navier-Stokes equation.
Posted by: oxford
Wed
7 Dec 2022
The off-shell sphere partition function, Tseytlin's prescriptions and black hole entropy
๐ London
Amr Ahmadain
(University of Cambridge)
Abstract:
The worldsheet theory of string backgrounds is a CFT with zero central charge. This is the definition of on-shell string theory. In off-shell string theory, on the other hand, conformal invariance on the worldsheet is explicitly broken, and the worldsheet theory is therefore a QFT rather than a CFT, with a UV cutoff.
In the first part of the talk, I will explain Tseytlinรขโฌโขs prescriptions for constructing classical (tree-level) off-shell effective actions and provide a general proof, using conformal perturbation theory, that it gives the correct equations of motion, to all orders in perturbation theory and รยฑรขโฌยฒ. I will also show how Tseytlin's prescriptions are equivalent to quotienting out by the gauge orbits of a regulated moduli space with "n" operator insertions.
In the second part of the talk, I will explain the underlying conceptual structure of the Susskind and Uglum black hole entropy argument. There I will show how the classical (tree-level) effective action and entropy S = A/4G_N can be calculated from the sphere diagrams.
Time permitting, I will also discuss ongoing work for deriving the holographic entanglement entropy (the RT formula) in AdS3/CFT2. I will end with mentioning some important insights into how the ER=EPR hypothesis can be implemented using tachyon condensation on orbifolds in string theory.
The worldsheet theory of string backgrounds is a CFT with zero central charge. This is the definition of on-shell string theory. In off-shell string theory, on the other hand, conformal invariance on the worldsheet is explicitly broken, and the worldsheet theory is therefore a QFT rather than a CFT, with a UV cutoff.
In the first part of the talk, I will explain Tseytlinรขโฌโขs prescriptions for constructing classical (tree-level) off-shell effective actions and provide a general proof, using conformal perturbation theory, that it gives the correct equations of motion, to all orders in perturbation theory and รยฑรขโฌยฒ. I will also show how Tseytlin's prescriptions are equivalent to quotienting out by the gauge orbits of a regulated moduli space with "n" operator insertions.
In the second part of the talk, I will explain the underlying conceptual structure of the Susskind and Uglum black hole entropy argument. There I will show how the classical (tree-level) effective action and entropy S = A/4G_N can be calculated from the sphere diagrams.
Time permitting, I will also discuss ongoing work for deriving the holographic entanglement entropy (the RT formula) in AdS3/CFT2. I will end with mentioning some important insights into how the ER=EPR hypothesis can be implemented using tachyon condensation on orbifolds in string theory.
Posted by: andrea
Tue
6 Dec 2022
Unitarity and clock dependence in quantum cosmology
Steffen Gielen
(University of Sheffield)
Abstract:
The problem of time is often discussed as an obstacle in canonical
quantisation of gravity: general covariance means there is no preferred
time parameter with respect to which evolution could be defined. We can
instead characterise dynamics in relational terms by defining one degree
of freedom to play the role of an internal clock for the other
variables; this leads to a "multiple choice problem". I will review
recent results obtained in a quantum cosmological model with three
dynamical degrees of freedom: a volume or scale factor variable for the
geometry, a massless scalar matter field, and a perfect fluid. Each of
these variables can be used as a clock for the other two. We obtain
three different theories which, if we require them to have unitary time
evolution with respect to the given clock, make very different
statements about the fate of the Universe. Only one resolves the
classical singularity, and only one leads to a quantum recollapse of the
Universe at large volume. Nonclassical behaviour arises whenever a
classical solution terminates in finite time so that reflecting boundary
conditions are needed to make the theory unitary.
The problem of time is often discussed as an obstacle in canonical
quantisation of gravity: general covariance means there is no preferred
time parameter with respect to which evolution could be defined. We can
instead characterise dynamics in relational terms by defining one degree
of freedom to play the role of an internal clock for the other
variables; this leads to a "multiple choice problem". I will review
recent results obtained in a quantum cosmological model with three
dynamical degrees of freedom: a volume or scale factor variable for the
geometry, a massless scalar matter field, and a perfect fluid. Each of
these variables can be used as a clock for the other two. We obtain
three different theories which, if we require them to have unitary time
evolution with respect to the given clock, make very different
statements about the fate of the Universe. Only one resolves the
classical singularity, and only one leads to a quantum recollapse of the
Universe at large volume. Nonclassical behaviour arises whenever a
classical solution terminates in finite time so that reflecting boundary
conditions are needed to make the theory unitary.
Posted by: IC
Mon
5 Dec 2022
Quantum theory of classical turbulence: Part 1
Alexander Migdal
(NYU)
Abstract:
A new approach to strong turbulence based on ideas of dynamical geometry and topological conservation laws is developed.
In terms of the quantum field theory, this is another example of the duality between a fluctuating vector field and fluctuating geometry.
Some new exact solutions of Navier-Stokes and Euler equations are found. The loop equation suggested in the early 90-ties is investigated in detail.
The loop equation plays the same role in our theory as the Boltzmann kinetic equation in statistical physics.
It has the form of the Schrรยถdinger equation with a complex Hamiltonian in loop space. The viscosity plays the role of Planck's constant.
Strong turbulence corresponds to the WKB limit of the loop equation.
In this limit, we find a fixed point of the loop equation we call Kelvinon.
Kelvinon has a conserved circulation for a fixed loop in space, generalizing Kelvin's theorem.
Clebsch field of this solution has nontrivial topology with two winding numbers.
These topological conservation laws allow us to compute the PDF of circulation in a WKB limit (large circulation in the viscosity units).
This PDF perfectly matches the results of numerical simulations of the conventional forced Navier-Stokes equation.
A new approach to strong turbulence based on ideas of dynamical geometry and topological conservation laws is developed.
In terms of the quantum field theory, this is another example of the duality between a fluctuating vector field and fluctuating geometry.
Some new exact solutions of Navier-Stokes and Euler equations are found. The loop equation suggested in the early 90-ties is investigated in detail.
The loop equation plays the same role in our theory as the Boltzmann kinetic equation in statistical physics.
It has the form of the Schrรยถdinger equation with a complex Hamiltonian in loop space. The viscosity plays the role of Planck's constant.
Strong turbulence corresponds to the WKB limit of the loop equation.
In this limit, we find a fixed point of the loop equation we call Kelvinon.
Kelvinon has a conserved circulation for a fixed loop in space, generalizing Kelvin's theorem.
Clebsch field of this solution has nontrivial topology with two winding numbers.
These topological conservation laws allow us to compute the PDF of circulation in a WKB limit (large circulation in the viscosity units).
This PDF perfectly matches the results of numerical simulations of the conventional forced Navier-Stokes equation.
Posted by: oxford
Mon
5 Dec 2022
Brane Brick Models for Fano 3-Folds and Ypk Manifolds
Rak-Kyeong Seong
(Ulsan National Institute of Science and Technology)
Abstract:
In this talk, I will discuss the construction of 2d (0,2) supersymmetric gauge theories corresponding to the 18 smooth Fano 3-folds and the families of Y^(p,k)(CP1xCP1) and Y^(p,k)(CP2) Sasaki-Einstein 7-manifolds. These 2d (0,2) gauge theories can be considered as the worldvolume theories of D1-branes probing toric Calabi-Yau 4-folds. The talk will illustrate how the map between gauge theory and the corresponding geometry is considerably simplified by a Type IIA brane configuration called brane brick models.
In this talk, I will discuss the construction of 2d (0,2) supersymmetric gauge theories corresponding to the 18 smooth Fano 3-folds and the families of Y^(p,k)(CP1xCP1) and Y^(p,k)(CP2) Sasaki-Einstein 7-manifolds. These 2d (0,2) gauge theories can be considered as the worldvolume theories of D1-branes probing toric Calabi-Yau 4-folds. The talk will illustrate how the map between gauge theory and the corresponding geometry is considerably simplified by a Type IIA brane configuration called brane brick models.
Posted by: IC2
Thu
1 Dec 2022
Gravity amplitudes, w 1+inf and color-kinematic
๐ London
Alfredo Guevara
(Harvard)
Abstract:
W-algebras are ubiquitous extended symmetries of a vast class of CFTs, with deep connections to quantum groups and integrability. Recently, through the techniques of celestial holography, the W_{1+inf} algebra was realized explicitly in celestial correlation functions associated to 4d gravitational scattering amplitudes, but the connection to other realizations of the symmetry, and in particular integrability, was vaguely understood. In this talk I will attempt to shed some light on this issue, arguing that the emergence of the symmetry is directly connected to the color-kinematics duality relating gravity and gauge theory amplitudes, at the same time unveiling an associative structure in collinear singularities of the tree-level S-Matrix.
W-algebras are ubiquitous extended symmetries of a vast class of CFTs, with deep connections to quantum groups and integrability. Recently, through the techniques of celestial holography, the W_{1+inf} algebra was realized explicitly in celestial correlation functions associated to 4d gravitational scattering amplitudes, but the connection to other realizations of the symmetry, and in particular integrability, was vaguely understood. In this talk I will attempt to shed some light on this issue, arguing that the emergence of the symmetry is directly connected to the color-kinematics duality relating gravity and gauge theory amplitudes, at the same time unveiling an associative structure in collinear singularities of the tree-level S-Matrix.
Posted by: QMW
Thu
1 Dec 2022
Effective description of quantum chaos and applications to black holes
๐ London
Felix Haehl
(Southampton)
Abstract:
After reviewing different aspects of thermalization and chaos in holographic quantum systems, I will argue that universal aspects can be captured using an effective field theory framework that shares similarities with hydrodynamics. Focusing on the quantum butterfly effect, I will explain how to develop a simple effective theory of the 'scramblon' from path integral considerations. I will also discuss applications of this formalism to shockwave scattering in black hole backgrounds in AdS/CFT.
After reviewing different aspects of thermalization and chaos in holographic quantum systems, I will argue that universal aspects can be captured using an effective field theory framework that shares similarities with hydrodynamics. Focusing on the quantum butterfly effect, I will explain how to develop a simple effective theory of the 'scramblon' from path integral considerations. I will also discuss applications of this formalism to shockwave scattering in black hole backgrounds in AdS/CFT.
Posted by: andrea
November 2022
Tue
29 Nov 2022
Positivity in EFTs with spontaneously broken boosts
Oliver Janssen
(ICTP, Trieste)
Abstract:
I will discuss positivity bounds on EFT coefficients in theories where Lorentz boosts are spontaneously broken. The well-known S-matrix argument from the Lorentz-invariant scenario does not straightforwardly generalize to this case. Instead the analytic properties of the retarded Greenรขโฌโขs function of conserved currents (or of the stress-energy tensor) will be used, and the theory will be assumed to become conformal in the UV. The method is general and applicable to both cosmology and condensed matter systems. As a concrete example we will consider the EFT of conformal superfluids, which describes the universal low-energy dynamics of CFTs at large U(1) charge, and we will derive inequalities on the coefficients of the operators, in three spacetime dimensions, at NLO and NNLO.
I will discuss positivity bounds on EFT coefficients in theories where Lorentz boosts are spontaneously broken. The well-known S-matrix argument from the Lorentz-invariant scenario does not straightforwardly generalize to this case. Instead the analytic properties of the retarded Greenรขโฌโขs function of conserved currents (or of the stress-energy tensor) will be used, and the theory will be assumed to become conformal in the UV. The method is general and applicable to both cosmology and condensed matter systems. As a concrete example we will consider the EFT of conformal superfluids, which describes the universal low-energy dynamics of CFTs at large U(1) charge, and we will derive inequalities on the coefficients of the operators, in three spacetime dimensions, at NLO and NNLO.
Posted by: IC
Mon
28 Nov 2022
LonTI: Introduction to Black Hole Microstate Counting
Sameer Murthy
(King's College London)
Abstract:
The pioneering work of Bekenstein and Hawking in the 1970s showed that black holes have thermodynamic properties like temperature and entropy in the quantum theory, just like the air in this room. This leads to the question: can we account for the thermodynamic entropy of a black hole as a statistical entropy of an ensemble of microscopic states? One of the big successes of string theory is to answer this question in the affirmative for a large class of black holes.
The pioneering work of Bekenstein and Hawking in the 1970s showed that black holes have thermodynamic properties like temperature and entropy in the quantum theory, just like the air in this room. This leads to the question: can we account for the thermodynamic entropy of a black hole as a statistical entropy of an ensemble of microscopic states? One of the big successes of string theory is to answer this question in the affirmative for a large class of black holes.
Posted by: lonti
Thu
24 Nov 2022
BRST Symmetry and Convolutional Double Copy
๐ London
Aritra Saha
(TAMU)
Abstract:
In this talk, I shall consider the convolutional double copy for BRST and anti-BRST covariant formulations of gravitational and gauge theories. I shall give a general BRST and anti-BRST invariant formulation of linearised \(\mathcal{N}=0\) supergravity using superspace methods and show how this may be obtained from the square of linearised Yang-Mills theories. I shall then demonstrate this relation for the Schwarzschild black hole and the ten-dimensional black string solution as two concrete examples.
In this talk, I shall consider the convolutional double copy for BRST and anti-BRST covariant formulations of gravitational and gauge theories. I shall give a general BRST and anti-BRST invariant formulation of linearised \(\mathcal{N}=0\) supergravity using superspace methods and show how this may be obtained from the square of linearised Yang-Mills theories. I shall then demonstrate this relation for the Schwarzschild black hole and the ten-dimensional black string solution as two concrete examples.
Posted by: QMW
Wed
23 Nov 2022
The off-shell sphere partition function, (Generalized) Tseytlin's prescriptions and black hole entropy
Amr Ahmadain
(University of Cambridge)
Abstract:
The worldsheet theory of string backgrounds is a CFT with zero central charge. This is the definition of on-shell string theory. In off-shell string theory, on the other hand, conformal invariance on the worldsheet is explicitly broken, and the worldsheet theory is therefore a QFT rather than a CFT, with a UV cutoff.
In this talk, I will explain Tseytlin's prescriptions for constructing classical (tree-level) off-shell effective actions and provide a general proof, using conformal perturbation theory, that it gives the correct equations of motion, to all orders in perturbation theory and \(\alpha'\). I will also show how Tseytlin's prescriptions are equivalent to quotienting out by the gauge orbits of a regulated moduli space with "n" operator insertions. I will also explain how Tseytlin's prescriptions encode the correct prescription for the Lorentzian S-matrix in which case we obtain Feynman's \(i\varepsilon\) prescription for the internal poles. Finally, I will explain how the classical off-shell string action was used by Susskind and Uglum to calculate the tree-level black hole entropy on a conical manifold in Rindler background.
Time permitting, I will present very recent upcoming work on a closed-form expression for a generalized Tseytlin (GT) operator that eliminates all spurious tadpoles from higher curvature couplings on the worldsheet. This allows us to study its action on correlations functions of scalar primaries and descendants with arbitrary conformal dimensions.
The worldsheet theory of string backgrounds is a CFT with zero central charge. This is the definition of on-shell string theory. In off-shell string theory, on the other hand, conformal invariance on the worldsheet is explicitly broken, and the worldsheet theory is therefore a QFT rather than a CFT, with a UV cutoff.
In this talk, I will explain Tseytlin's prescriptions for constructing classical (tree-level) off-shell effective actions and provide a general proof, using conformal perturbation theory, that it gives the correct equations of motion, to all orders in perturbation theory and \(\alpha'\). I will also show how Tseytlin's prescriptions are equivalent to quotienting out by the gauge orbits of a regulated moduli space with "n" operator insertions. I will also explain how Tseytlin's prescriptions encode the correct prescription for the Lorentzian S-matrix in which case we obtain Feynman's \(i\varepsilon\) prescription for the internal poles. Finally, I will explain how the classical off-shell string action was used by Susskind and Uglum to calculate the tree-level black hole entropy on a conical manifold in Rindler background.
Time permitting, I will present very recent upcoming work on a closed-form expression for a generalized Tseytlin (GT) operator that eliminates all spurious tadpoles from higher curvature couplings on the worldsheet. This allows us to study its action on correlations functions of scalar primaries and descendants with arbitrary conformal dimensions.
Posted by: IC2
Wed
23 Nov 2022
Bootstrapping line defects with O(2) symmetry
๐ London
Philine van Vliet
(DESY)
Abstract:
Line defects play an important role in our understanding of QFTs, explaining interesting phenomena in both condensed matter physics and high-energy theories, and giving access to new data and observables.
I will discuss recent work in which we explore 1d conformal line defects with an additional O(2) symmetry using the numerical bootstrap. The starting point is an agnostic approach, where we perfom a systematic bootstrap study of correlation functions between two canonical defect operators: the displacement and the tilt. We then move on to study two specific defects: a monodromy line defect and a localized magnetic field line defect. I will highlight the results of the latter one, where we found a series of intriguing cusps which we investigate.
Line defects play an important role in our understanding of QFTs, explaining interesting phenomena in both condensed matter physics and high-energy theories, and giving access to new data and observables.
I will discuss recent work in which we explore 1d conformal line defects with an additional O(2) symmetry using the numerical bootstrap. The starting point is an agnostic approach, where we perfom a systematic bootstrap study of correlation functions between two canonical defect operators: the displacement and the tilt. We then move on to study two specific defects: a monodromy line defect and a localized magnetic field line defect. I will highlight the results of the latter one, where we found a series of intriguing cusps which we investigate.
Posted by: andrea
Tue
22 Nov 2022
Gravitational wave generation in effective field theories of dark energy
Enrico Barausse
(SISSA, Trieste)
Abstract:
I will review how non-linearities can allow for screening solar-system scales from non-tensorial gravitational polarizations, focusing on the case of scalar-tensor theories with derivative self-interactions (K-essence). I will then present fully relativistic simulations in these theories in 1+1 dimensions (stellar oscillations and collapse) and 3+1 dimensions (binary neutron stars), showing how to avoid breakdowns of the Cauchy problem that have affected similar attempts in the past. I will show that screening tends to suppress the (subdominant) dipole scalar emission in binary neutron star systems, but that it fails to quench monopole scalar emission in gravitational collapse, and quadrupole scalar emission in binaries.
I will review how non-linearities can allow for screening solar-system scales from non-tensorial gravitational polarizations, focusing on the case of scalar-tensor theories with derivative self-interactions (K-essence). I will then present fully relativistic simulations in these theories in 1+1 dimensions (stellar oscillations and collapse) and 3+1 dimensions (binary neutron stars), showing how to avoid breakdowns of the Cauchy problem that have affected similar attempts in the past. I will show that screening tends to suppress the (subdominant) dipole scalar emission in binary neutron star systems, but that it fails to quench monopole scalar emission in gravitational collapse, and quadrupole scalar emission in binaries.
Posted by: IC
Mon
21 Nov 2022
LonTI: Introduction to Black Hole Microstate Counting
Sameer Murthy
(King's College London)
Abstract:
The pioneering work of Bekenstein and Hawking in the 1970s showed that black holes have thermodynamic properties like temperature and entropy in the quantum theory, just like the air in this room. This leads to the question: can we account for the thermodynamic entropy of a black hole as a statistical entropy of an ensemble of microscopic states? One of the big successes of string theory is to answer this question in the affirmative for a large class of black holes.
The pioneering work of Bekenstein and Hawking in the 1970s showed that black holes have thermodynamic properties like temperature and entropy in the quantum theory, just like the air in this room. This leads to the question: can we account for the thermodynamic entropy of a black hole as a statistical entropy of an ensemble of microscopic states? One of the big successes of string theory is to answer this question in the affirmative for a large class of black holes.
Posted by: lonti
Thu
17 Nov 2022
Coactions of Feynman periods from integrability
๐ London
Omer Gurdogan
(Southampton)
Abstract:
Results in Quantum Field Theories, such as anomalous dimensions or
scattering amplitudes are known to exhibit rich properities under the
Galois coaction that acts on period integrals. I will show how these
phenomena arise directly from an integrability setup describing
certain anomalous dimensions of an integrable four-dimensional scalar
model. I will also discuss a conjectural all-loop differential
equation for these quantities, constructed from derivatives with
respect to Riemann zeta values.
Results in Quantum Field Theories, such as anomalous dimensions or
scattering amplitudes are known to exhibit rich properities under the
Galois coaction that acts on period integrals. I will show how these
phenomena arise directly from an integrability setup describing
certain anomalous dimensions of an integrable four-dimensional scalar
model. I will also discuss a conjectural all-loop differential
equation for these quantities, constructed from derivatives with
respect to Riemann zeta values.
Posted by: QMW
Wed
16 Nov 2022
Mixed anomalies and generalized symmetries from 3d superconformal indices
Matteo Sacchi
(University of Oxford)
Abstract:
Mixed anomalies and generalized symmetries have proved to be useful in providing non-trivial constraints on the dynamics of quantum field theories (QFTs). A natural question is whether these are related in any way to certain supersymmetric partition functions or indices, which have also been used extensively to study the dynamics of QFTs. In this talk, we address this question in the context of 3d Nรขโฐยฅ3 gauge theories using the superconformal index. In particular, using the index we are able to detect mixed anomalies involving discrete 0-form global symmetries, and possibly a 1-form symmetry. The effectiveness of this method is demonstrated via several classes of theories, including Chern-Simons-matter theories, the T(SU(N)) theory of Gaiotto-Witten and variants of the Aharony-Bergman-Jafferis (ABJ) theory with the orthosymplectic gauge algebra. Gauging appropriate global symmetries involved in mixed anomalies of some of these models and using constructions available in the literature, we obtain various interesting theories with two-group structures or non-invertible symmetries.
Mixed anomalies and generalized symmetries have proved to be useful in providing non-trivial constraints on the dynamics of quantum field theories (QFTs). A natural question is whether these are related in any way to certain supersymmetric partition functions or indices, which have also been used extensively to study the dynamics of QFTs. In this talk, we address this question in the context of 3d Nรขโฐยฅ3 gauge theories using the superconformal index. In particular, using the index we are able to detect mixed anomalies involving discrete 0-form global symmetries, and possibly a 1-form symmetry. The effectiveness of this method is demonstrated via several classes of theories, including Chern-Simons-matter theories, the T(SU(N)) theory of Gaiotto-Witten and variants of the Aharony-Bergman-Jafferis (ABJ) theory with the orthosymplectic gauge algebra. Gauging appropriate global symmetries involved in mixed anomalies of some of these models and using constructions available in the literature, we obtain various interesting theories with two-group structures or non-invertible symmetries.
Posted by: IC2
Wed
16 Nov 2022
Semiclassics for Large Quantum Numbers
๐ London
Mark Mezei
(Oxford)
Abstract:
According to the correspondence principle, classical physics emerges in the limit of large quantum numbers. We examine two examples of the semiclassical description of conformal field theory data: large spin impurities in the free triplet scalar field theory and large charge Wilson lines in QED. By simultaneously taking the coupling to zero and quantum numbers to infinity, we can connect the microscopic to the emergent classical description smoothly.
According to the correspondence principle, classical physics emerges in the limit of large quantum numbers. We examine two examples of the semiclassical description of conformal field theory data: large spin impurities in the free triplet scalar field theory and large charge Wilson lines in QED. By simultaneously taking the coupling to zero and quantum numbers to infinity, we can connect the microscopic to the emergent classical description smoothly.
Posted by: andrea
Tue
15 Nov 2022
A Chern-Simons Theory for the North Atlantic Ocean
David Tong
(University of Cambridge)
Abstract:
In some ways the ocean acts like a topological insulator. There are chiral edge modes, localised at the coast, that go clockwise in the Northern hemisphere and anti-clockwise in the Southern hemisphere. Iรขโฌโขll describe these features and explain how this can be understood in terms of something more familiar to high energy physicists. Iรขโฌโขll show that the equations that govern the long-time dynamics of the ocean can be recast as a Maxwell-Chern-Simons theory.
In some ways the ocean acts like a topological insulator. There are chiral edge modes, localised at the coast, that go clockwise in the Northern hemisphere and anti-clockwise in the Southern hemisphere. Iรขโฌโขll describe these features and explain how this can be understood in terms of something more familiar to high energy physicists. Iรขโฌโขll show that the equations that govern the long-time dynamics of the ocean can be recast as a Maxwell-Chern-Simons theory.
Posted by: IC
Mon
14 Nov 2022
LonTI: Introduction to Black Hole Microstate Counting
Sameer Murthy
(King's College London)
Abstract:
The pioneering work of Bekenstein and Hawking in the 1970s showed that black holes have thermodynamic properties like temperature and entropy in the quantum theory, just like the air in this room. This leads to the question: can we account for the thermodynamic entropy of a black hole as a statistical entropy of an ensemble of microscopic states? One of the big successes of string theory is to answer this question in the affirmative for a large class of black holes.
The pioneering work of Bekenstein and Hawking in the 1970s showed that black holes have thermodynamic properties like temperature and entropy in the quantum theory, just like the air in this room. This leads to the question: can we account for the thermodynamic entropy of a black hole as a statistical entropy of an ensemble of microscopic states? One of the big successes of string theory is to answer this question in the affirmative for a large class of black holes.
Posted by: lonti
Thu
10 Nov 2022
Holographic thermal correlators from supersymmetric instantons.
๐ London
Alba Grassi
(University of Geneva and CERN)
Abstract:
I will present an exact formula for the thermal scalar two-point function in four-dimensional holographic conformal field theories. The problem of finding it reduces to the analysis of the wave equation on the AdS-Schwarzschild background. The two-point function is computed from the connection coefficients of the Heun equation, which can be expressed in terms of the Nekrasov-Shatashvili partition function of an SU(2) supersymmetric gauge theory with four fundamental hypermultiplets. At large spin the instanton expansion of the thermal two-point function directly maps to the light-cone bootstrap analysis of the heavy-light four-point function. Using this connection, we obtain the OPE data of heavy-light double-twist operators directly from instanton counting in the SU(2) gauge theory.
I will present an exact formula for the thermal scalar two-point function in four-dimensional holographic conformal field theories. The problem of finding it reduces to the analysis of the wave equation on the AdS-Schwarzschild background. The two-point function is computed from the connection coefficients of the Heun equation, which can be expressed in terms of the Nekrasov-Shatashvili partition function of an SU(2) supersymmetric gauge theory with four fundamental hypermultiplets. At large spin the instanton expansion of the thermal two-point function directly maps to the light-cone bootstrap analysis of the heavy-light four-point function. Using this connection, we obtain the OPE data of heavy-light double-twist operators directly from instanton counting in the SU(2) gauge theory.
Posted by: QMW
Wed
9 Nov 2022
A dispersion relation for bootstrapping holographic defect correlators
Julien Barrat
(Humboldt University of Berlin)
Abstract:
Tremendous progress has been achieved during the last years in bootstrapping conformal correlators at strong coupling using analytical bootstrap methods and the AdS/CFT correspondence. In particular, the development of Lorentzian inversion formulae revealed helpful in reconstructing four-point functions. In this talk I will present how this technology can be adapted to defect setups in order to compute scalar two-point functions in the presence of a conformal defect in the strong-coupling regime. We derived a dispersion relation that allows to efficiently generate elegant closed-form expressions for a variety of setups, and in particular we apply this method to two-point functions of single-trace half-BPS operators in the presence of the supersymmetric Wilson line defect in 4d N=4 SYM, using minimal input from holography.
Tremendous progress has been achieved during the last years in bootstrapping conformal correlators at strong coupling using analytical bootstrap methods and the AdS/CFT correspondence. In particular, the development of Lorentzian inversion formulae revealed helpful in reconstructing four-point functions. In this talk I will present how this technology can be adapted to defect setups in order to compute scalar two-point functions in the presence of a conformal defect in the strong-coupling regime. We derived a dispersion relation that allows to efficiently generate elegant closed-form expressions for a variety of setups, and in particular we apply this method to two-point functions of single-trace half-BPS operators in the presence of the supersymmetric Wilson line defect in 4d N=4 SYM, using minimal input from holography.
Posted by: IC2
Wed
9 Nov 2022
Celestial amplitudes from flat space limits of AdS/Witten diagrams
๐ London
Ana-Maria Raclariu
(Amsterdam)
Abstract:
The search for pragmatic observables of quantum gravity remains at the forefront of fundamental physics research. A large set of ideas collectively known as the gauge-gravity duality have proven fruitful in tackling this problem. While such a duality is believed to universally govern gravitational theories, its nature in theories of gravity that describe our universe to a good degree of approximation is still little understood.
In this talk I will discuss efforts in formulating a holographic correspondence for gravity in four-dimensional asymptotically flat spacetimes. The proposed dual theory lives on a two-dimensional celestial sphere at infinity and is constrained by a wide range of symmetries. I present recent evidence for this proposal by showing that it arises naturally in a flat space limit of AdS/CFT. I will illustrate this construction with two related examples: the propagation of a particle in a shockwave background and the high-energy scattering of 2 particles.
The search for pragmatic observables of quantum gravity remains at the forefront of fundamental physics research. A large set of ideas collectively known as the gauge-gravity duality have proven fruitful in tackling this problem. While such a duality is believed to universally govern gravitational theories, its nature in theories of gravity that describe our universe to a good degree of approximation is still little understood.
In this talk I will discuss efforts in formulating a holographic correspondence for gravity in four-dimensional asymptotically flat spacetimes. The proposed dual theory lives on a two-dimensional celestial sphere at infinity and is constrained by a wide range of symmetries. I present recent evidence for this proposal by showing that it arises naturally in a flat space limit of AdS/CFT. I will illustrate this construction with two related examples: the propagation of a particle in a shockwave background and the high-energy scattering of 2 particles.
Posted by: andrea
Tue
8 Nov 2022
Surprises in the 2d O(n) model
๐ London
Victor Gorbenko
(EPFL)
Abstract:
I will discuss the two-dimensional O(n) model for a continuous range of n. It can be defined non-perturbatively for any n as an infrared limit of certain lattice loop models, which in the IR give rise to two families of CFTs. For n<2 these CFTs are logarithmic, while for n>2 they are also complex. For n<2 the RG flow to the fixed points violates the straightforward notion of naturalness and appears tuned.
I will discuss the two-dimensional O(n) model for a continuous range of n. It can be defined non-perturbatively for any n as an infrared limit of certain lattice loop models, which in the IR give rise to two families of CFTs. For n<2 these CFTs are logarithmic, while for n>2 they are also complex. For n<2 the RG flow to the fixed points violates the straightforward notion of naturalness and appears tuned.
Posted by: andrea
Tue
8 Nov 2022
Non-perturbative S-matrices from dispersive iteration
Piotr Tourkine
(LAPTh, Annecy)
Abstract:
In 1968, D. Atkinson proved in a series of papers the existence of functions satisfying all known constraints of the S-matrix bootstrap for the 2-to-2 S-matrix of gapped theories. To date, this is the only result of this sort, while a contrario no current technology allows to generate, even numerically, fully consistent S-matrices in d>2. Beyond the mathematical results themselves, the proof, based on establishing the existence of a fixed point of a certain map, also suggests a procedure to be implemented numerically and which would produce fully consistent S-matrix functions via iterating dispersion relations, and using as an input a quantity related to the inelasticity of a given scattering process. In this talk, I will report on some work being finalised, done in collaboration with A. Zhiboedov, about analytical and numerical aspects of developing and implementing this scheme. I will review basic concepts of the S-matrix program and show some of our results on non-perturbative scalar, phi^4-like S-matrices in 4, describe their properties and compare to other approaches in the literature. If time allows, I will present some results in 3 dimensions and discuss subtle aspects of the high energy (Regge behaviour) of the S-matrices.
In 1968, D. Atkinson proved in a series of papers the existence of functions satisfying all known constraints of the S-matrix bootstrap for the 2-to-2 S-matrix of gapped theories. To date, this is the only result of this sort, while a contrario no current technology allows to generate, even numerically, fully consistent S-matrices in d>2. Beyond the mathematical results themselves, the proof, based on establishing the existence of a fixed point of a certain map, also suggests a procedure to be implemented numerically and which would produce fully consistent S-matrix functions via iterating dispersion relations, and using as an input a quantity related to the inelasticity of a given scattering process. In this talk, I will report on some work being finalised, done in collaboration with A. Zhiboedov, about analytical and numerical aspects of developing and implementing this scheme. I will review basic concepts of the S-matrix program and show some of our results on non-perturbative scalar, phi^4-like S-matrices in 4, describe their properties and compare to other approaches in the literature. If time allows, I will present some results in 3 dimensions and discuss subtle aspects of the high energy (Regge behaviour) of the S-matrices.
Posted by: IC
Mon
7 Nov 2022
LonTI: Introduction to Black Hole Microstate Counting
Sameer Murthy
(King's College London)
Abstract:
The pioneering work of Bekenstein and Hawking in the 1970s showed that black holes have thermodynamic properties like temperature and entropy in the quantum theory, just like the air in this room. This leads to the question: can we account for the thermodynamic entropy of a black hole as a statistical entropy of an ensemble of microscopic states? One of the big successes of string theory is to answer this question in the affirmative for a large class of black holes.
The pioneering work of Bekenstein and Hawking in the 1970s showed that black holes have thermodynamic properties like temperature and entropy in the quantum theory, just like the air in this room. This leads to the question: can we account for the thermodynamic entropy of a black hole as a statistical entropy of an ensemble of microscopic states? One of the big successes of string theory is to answer this question in the affirmative for a large class of black holes.
Posted by: lonti
Mon
7 Nov 2022
The quantum deformed Haldane-Shastry model at root of unity
๐ London
Didina Serban
(IPhT Saclay)
Abstract:
I will present an ongoing work on an integrable long-range deformation of the XXZ spin chain which can also be seen as a quantum deformation of the Haldane-Shastry model. At generic values for the deformation parameter, the model possess quantum affine symmetry, but when q is root of unity we expect extra symmetries to occur. We are studying the case q=i, which in the nearest neighbour case is solvable by the Jordan-Wigner transformation. The long-range case is also reducible to a fermionic long-range model. I will discuss the main characteristics of the model, which are very different for the even and odd number of sites.
I will present an ongoing work on an integrable long-range deformation of the XXZ spin chain which can also be seen as a quantum deformation of the Haldane-Shastry model. At generic values for the deformation parameter, the model possess quantum affine symmetry, but when q is root of unity we expect extra symmetries to occur. We are studying the case q=i, which in the nearest neighbour case is solvable by the Jordan-Wigner transformation. The long-range case is also reducible to a fermionic long-range model. I will discuss the main characteristics of the model, which are very different for the even and odd number of sites.
Posted by: andrea
Fri
4 Nov 2022
Chern-Simons Gravity and Neutrino Self-Interactions
Cyril Creque-Sarbinowski
(Center for Computational Astrophysics at the Flatiron Institute)
Abstract:
Dynamical Chern-Simons gravity (dCS) is a four-dimensional parity-violating extension of general relativity. Current models predict the effect of this extension to be negligible due to large decay constants f close to the scale of grand unified theories. Here, we present a construction of dCS allowing for much smaller decay constants, ranging from sub-eV to Planck scales. Specifically, we show that if there exists a fermion species with strong self-interactions, the short-wavelength fermion modes form a bound state. This bound state can then undergo dynamical symmetry breaking and the resulting pseudoscalar develops Yukawa interactions with the remaining long-wavelength fermion modes. Due to this new interaction, loop corrections with gravitons then realize a linear coupling between the pseudoscalar and the gravitational Chern-Simons term. The strength of this coupling is set by the Yukawa coupling constant divided by the fermion mass. Therefore, since self-interacting fermions with small masses are ideal, we identify neutrinos as promising candidates. For example, if a neutrino has a mass mรยฝ รขโฐยฒmeV and the Yukawa coupling is order unity, the dCS decay constant can be as small as fรขหยผ10^3mรยฝ รขโฐยฒeV. We discuss other potential choices for fermions.
Dynamical Chern-Simons gravity (dCS) is a four-dimensional parity-violating extension of general relativity. Current models predict the effect of this extension to be negligible due to large decay constants f close to the scale of grand unified theories. Here, we present a construction of dCS allowing for much smaller decay constants, ranging from sub-eV to Planck scales. Specifically, we show that if there exists a fermion species with strong self-interactions, the short-wavelength fermion modes form a bound state. This bound state can then undergo dynamical symmetry breaking and the resulting pseudoscalar develops Yukawa interactions with the remaining long-wavelength fermion modes. Due to this new interaction, loop corrections with gravitons then realize a linear coupling between the pseudoscalar and the gravitational Chern-Simons term. The strength of this coupling is set by the Yukawa coupling constant divided by the fermion mass. Therefore, since self-interacting fermions with small masses are ideal, we identify neutrinos as promising candidates. For example, if a neutrino has a mass mรยฝ รขโฐยฒmeV and the Yukawa coupling is order unity, the dCS decay constant can be as small as fรขหยผ10^3mรยฝ รขโฐยฒeV. We discuss other potential choices for fermions.
Posted by: IC
Wed
2 Nov 2022
Symmetry TFT and Non-invertible Symmetries (seminar cancelled)
Sakura Schafer-Nameki
(University of Oxford)
Abstract:
The seminar has been cancelled.
The seminar has been cancelled.
Posted by: IC2
Wed
2 Nov 2022
Double holography and Page curves in Type IIB
๐ London
Christoph Uhlemann
(Oxford)
Tue
1 Nov 2022
LonTI: Lectures on the duality between the Sine-Gordon and the Thirring model
Alessandro Torrielli
(University of Surrey)
Abstract:
We will describe the duality between two integrable systems: the 2D Sine-Gordon model and the 2D Thirring model. We will spend some time describing the classical and quantum Sine-Gordon model, in particular its spectrum, S-matrices and underlying quantum-group symmetry. We will then present the duality with the Thirring model as originally stated by Coleman and refined in subsequent literature. All the basic elements will be provided without relying on too many pre-requisites beyond standard graduate-level quantum field theory. The notes comprise a series of exercises.
We will describe the duality between two integrable systems: the 2D Sine-Gordon model and the 2D Thirring model. We will spend some time describing the classical and quantum Sine-Gordon model, in particular its spectrum, S-matrices and underlying quantum-group symmetry. We will then present the duality with the Thirring model as originally stated by Coleman and refined in subsequent literature. All the basic elements will be provided without relying on too many pre-requisites beyond standard graduate-level quantum field theory. The notes comprise a series of exercises.
Posted by: lonti
Tue
1 Nov 2022
Pure supergravity and the conformal bootstrap
Shai Chester
(Jefferson Physical Laboratory, Harvard University)
Abstract:
We consider graviton scattering in maximal supergravity on Anti-de Sitter space (AdS) in d+1 dimensions for d=3,4,and 6 with no extra compact spacetime factor. Holography suggests that this theory is dual to an exotic maximally supersymmetric conformal field theory (CFT) in d dimensions whose only light single trace operator is the stress tensor. This contrasts with more standard cases like Type IIB string theory on AdS_5x S^5 dual to N=4 Super-Yang-Mills, where the CFT has light single trace operators for each Kaluza-Klein mode on S^5. We compute the 1-loop correction to the pure AdS_{d+1} theory in a small Planck length expansion, which is dual to the large central charge expansion in the CFT. We find that this correction saturates the most general non-perturbative conformal bootstrap bounds on this correlator in the large central charge regime for d=3,4,6. After imposing theory-specific constraints from localization in d=3,4, the bootstrap constraints strengthen and are then saturated by the string/M-theory dual CFT data.
We consider graviton scattering in maximal supergravity on Anti-de Sitter space (AdS) in d+1 dimensions for d=3,4,and 6 with no extra compact spacetime factor. Holography suggests that this theory is dual to an exotic maximally supersymmetric conformal field theory (CFT) in d dimensions whose only light single trace operator is the stress tensor. This contrasts with more standard cases like Type IIB string theory on AdS_5x S^5 dual to N=4 Super-Yang-Mills, where the CFT has light single trace operators for each Kaluza-Klein mode on S^5. We compute the 1-loop correction to the pure AdS_{d+1} theory in a small Planck length expansion, which is dual to the large central charge expansion in the CFT. We find that this correction saturates the most general non-perturbative conformal bootstrap bounds on this correlator in the large central charge regime for d=3,4,6. After imposing theory-specific constraints from localization in d=3,4, the bootstrap constraints strengthen and are then saturated by the string/M-theory dual CFT data.
Posted by: IC
Tue
1 Nov 2022
Skyrmions: Colloquium + Book Launch
Nick Manton
(Cambridge University)
Abstract:
https://lims.ac.uk/event/skyrme-theory-at-60/
Prof. Nick Manton, FRS, will give a colloquium on Skyrmions, followed by book launch and reception, celebrating his latest book on the subject, in the historic Faraday Suites of the London Institute for Mathematical Sciences (LIMS).
Schedule
2 - 3 Colloquium
3 - 3:30 Introduction by Prof. Yang-Hui He, Fellow of LIMS
3:30 - 5 Book launch + Reception: Prof. Manton
Address: LIMS, Royal Institution, 21 Albemarle St., Mayfair.
https://lims.ac.uk/event/skyrme-theory-at-60/
Prof. Nick Manton, FRS, will give a colloquium on Skyrmions, followed by book launch and reception, celebrating his latest book on the subject, in the historic Faraday Suites of the London Institute for Mathematical Sciences (LIMS).
Schedule
2 - 3 Colloquium
3 - 3:30 Introduction by Prof. Yang-Hui He, Fellow of LIMS
3:30 - 5 Book launch + Reception: Prof. Manton
Address: LIMS, Royal Institution, 21 Albemarle St., Mayfair.
Posted by: oxford
October 2022
Thu
27 Oct 2022
Quantum games for many-body physics
๐ London
Fiona Burnell
( University of Minnesota)
Abstract:
One way of probing quantum entanglement is to identify a multi-player task (a รขโฌลgameรขโฌย) that can be won more reliably when the players share a specific entangled quantum state. I will review some well-known quantum games, and discuss how these can be generalized to games which exploit the entanglement structure of a phase of matter rather than a specific quantum state.
One way of probing quantum entanglement is to identify a multi-player task (a รขโฌลgameรขโฌย) that can be won more reliably when the players share a specific entangled quantum state. I will review some well-known quantum games, and discuss how these can be generalized to games which exploit the entanglement structure of a phase of matter rather than a specific quantum state.
Posted by: QMW
Wed
26 Oct 2022
From ExFT to non-SUSY conformal manifolds
Colin Sterckx
(Universite Libre de Bruxelles)
Abstract:
We will review a recent application of Exceptional Field Theory : finding new families of solutions of type IIB supergravity on AdS_4 x S^1 x S^5. To find such solutions, we will compactify type IIB on S^5 x S^1 to obtain a 4d gauged maximal supergravity where new solutions are simply found by extremising a scalar potential. Surprisingly, it is sometime possible to deform our new solutions and break any residual supersymmetry while preserving stability. This is surprising since, from a holographic perspective, these deformations should be dual to non-supersymmetric exactly marginal deformations. We will show that it is a generic behaviour of gravity theories compactified on a circle and we will provide a solution generating technique in terms of a tool called the mapping torus.
We will review a recent application of Exceptional Field Theory : finding new families of solutions of type IIB supergravity on AdS_4 x S^1 x S^5. To find such solutions, we will compactify type IIB on S^5 x S^1 to obtain a 4d gauged maximal supergravity where new solutions are simply found by extremising a scalar potential. Surprisingly, it is sometime possible to deform our new solutions and break any residual supersymmetry while preserving stability. This is surprising since, from a holographic perspective, these deformations should be dual to non-supersymmetric exactly marginal deformations. We will show that it is a generic behaviour of gravity theories compactified on a circle and we will provide a solution generating technique in terms of a tool called the mapping torus.
Posted by: IC2
Wed
26 Oct 2022
Boundary critical behaviour: phenomenology, models, and field theory
๐ London
Hans Diehl
(Duisburg-Essen)
Abstract:
Boundary critical behaviours of systems at bulk criticality have been studied by condensed matter physicists for decades, in the beginning mostly theoretically, then also experimentally. These studies have revealed that the field of boundary critical phenomena is quite rich. For any universality class of bulk critical behaviour usually several distinct universality classes of boundary critical behaviour exist. To elucidate this, we introduce appropriate lattice models and map them onto boundary field theories describing their scale and conformal invariance on large scales. We show that this mapping can be subtle in some cases. We discuss the role and difference of boundary conditions of the field theories on mesoscopic and large scales, to what extent they are characteristic of –- and hence may be used to identify –- the distinct boundary universality classes. Finally, we explain the characteristic near-boundary asymptotic behaviours they exhibit and mention some open problems.
Boundary critical behaviours of systems at bulk criticality have been studied by condensed matter physicists for decades, in the beginning mostly theoretically, then also experimentally. These studies have revealed that the field of boundary critical phenomena is quite rich. For any universality class of bulk critical behaviour usually several distinct universality classes of boundary critical behaviour exist. To elucidate this, we introduce appropriate lattice models and map them onto boundary field theories describing their scale and conformal invariance on large scales. We show that this mapping can be subtle in some cases. We discuss the role and difference of boundary conditions of the field theories on mesoscopic and large scales, to what extent they are characteristic of –- and hence may be used to identify –- the distinct boundary universality classes. Finally, we explain the characteristic near-boundary asymptotic behaviours they exhibit and mention some open problems.
Posted by: andrea
Tue
25 Oct 2022
Cosmological aspects of non-local infinite derivative gravity theories
Alexey Koshelev
(UBI)
Abstract:
In my talk I will review the recent progress in non-local infinite derivative gravity theories. The core of the models under investigation is the infinite derivative generalization of the quadratic gravity theory which was first studied in depth by Stelle in 1977. I will explain why unitarity can only be restored for an infinite tower of derivatives. The rest of the talk will concentrate on the cosmological consequences of this non-local gravity proposal for the Starobinsky inflation.
In my talk I will review the recent progress in non-local infinite derivative gravity theories. The core of the models under investigation is the infinite derivative generalization of the quadratic gravity theory which was first studied in depth by Stelle in 1977. I will explain why unitarity can only be restored for an infinite tower of derivatives. The rest of the talk will concentrate on the cosmological consequences of this non-local gravity proposal for the Starobinsky inflation.
Posted by: IC
Mon
24 Oct 2022
LonTI: Lectures on the duality between the Sine-Gordon and the Thirring model
Alessandro Torrielli
(University of Surrey)
Abstract:
We will describe the duality between two integrable systems: the 2D Sine-Gordon model and the 2D Thirring model. We will spend some time describing the classical and quantum Sine-Gordon model, in particular its spectrum, S-matrices and underlying quantum-group symmetry. We will then present the duality with the Thirring model as originally stated by Coleman and refined in subsequent literature. All the basic elements will be provided without relying on too many pre-requisites beyond standard graduate-level quantum field theory. The notes comprise a series of exercises.
We will describe the duality between two integrable systems: the 2D Sine-Gordon model and the 2D Thirring model. We will spend some time describing the classical and quantum Sine-Gordon model, in particular its spectrum, S-matrices and underlying quantum-group symmetry. We will then present the duality with the Thirring model as originally stated by Coleman and refined in subsequent literature. All the basic elements will be provided without relying on too many pre-requisites beyond standard graduate-level quantum field theory. The notes comprise a series of exercises.
Posted by: lonti
Fri
21 Oct 2022
Large N Partition Functions, Holography, and Black Holes
Nikolay Bobev
(KU Leuven)
Abstract:
I will discuss the large N behavior of partition functions of the ABJM theory on compact Euclidean manifolds. I will pay particular attention to the S^3 free energy and the topologically twisted index for which I will present closed form expressions valid to all orders in the large N expansion. These results have important implications for holography and the microscopic entropy counting of AdS_4 black holes which I will discuss. I will also briefly discuss generalizations to other SCFTs arising from M2-branes.
I will discuss the large N behavior of partition functions of the ABJM theory on compact Euclidean manifolds. I will pay particular attention to the S^3 free energy and the topologically twisted index for which I will present closed form expressions valid to all orders in the large N expansion. These results have important implications for holography and the microscopic entropy counting of AdS_4 black holes which I will discuss. I will also briefly discuss generalizations to other SCFTs arising from M2-branes.
Posted by: IC2
Thu
20 Oct 2022
Quantum annealers as tools for theory
๐ London
Steve Abel
(Durham)
Abstract:
Quantum annealers are near-term adiabatic quantum computing devices that are already of significant size. In this talk I discuss how they can be used as laboratories to implement genuine tunnelling in Quantum Field Theories. I also discuss how they can be used to embed and train a general neural network in a quantum annealer without introducing any classical element in training. This approach opens a novel avenue for the quantum training of general machine learning models which can incorporate virtually limitless and changing training data. The talk will include a pedagogical introduction to quantum annealing.
Quantum annealers are near-term adiabatic quantum computing devices that are already of significant size. In this talk I discuss how they can be used as laboratories to implement genuine tunnelling in Quantum Field Theories. I also discuss how they can be used to embed and train a general neural network in a quantum annealer without introducing any classical element in training. This approach opens a novel avenue for the quantum training of general machine learning models which can incorporate virtually limitless and changing training data. The talk will include a pedagogical introduction to quantum annealing.
Posted by: QMW
Wed
19 Oct 2022
BMS flux algebra and loop-corrections to soft graviton theorems
๐ London
Kevin Nguyen
(KCL)
Abstract:
I will discuss recent developments in the characterisation of asymptotic states in asymptotically flat gravity, and the central role played by BMS fluxes in connection to soft graviton theorems. As a result of these new ideas, I will show that the subleading soft graviton theorem including loop effects is the Ward identity associated with superrotations symmetries. We will conclude that BMS symmetries are genuine symmetries of the gravitational S-matrix beyond the classical regime.
I will discuss recent developments in the characterisation of asymptotic states in asymptotically flat gravity, and the central role played by BMS fluxes in connection to soft graviton theorems. As a result of these new ideas, I will show that the subleading soft graviton theorem including loop effects is the Ward identity associated with superrotations symmetries. We will conclude that BMS symmetries are genuine symmetries of the gravitational S-matrix beyond the classical regime.
Posted by: QMW
Wed
19 Oct 2022
Strong dynamical fluctuations and spontaneous symmetry breaking in fracton fluids
๐ London
Paolo Glorioso
(Stanford)
Abstract:
Fracton phases are characterized by their elementary excitations having restricted mobility, and have recently been of relevance in several subjects, from quantum information to thermalization, from gravity to elasticity. In the context of hydrodynamics it has been shown theoretically, and confirmed experimentally, that such restricted mobility leads to novel emergent scaling laws. In this talk, I will introduce a framework to describe the hydrodynamics of fractons and predict such scaling laws, with particular focus on systems with conserved dipole and momentum. This hydrodynamics turns out to have rather exotic properties, owing to the fact that dipole conservation leads to a non-trivial extension of spacetime symmetries. After developing an effective theory approach that allows accounting for fluctuations, I will show that such theory contains relevant nonlinearities that lead to the emergence of stochastic non-Gaussian universality classes, even in three spatial dimensions, thus constituting a breakdown of its local hydrodynamic description.
Fracton phases are characterized by their elementary excitations having restricted mobility, and have recently been of relevance in several subjects, from quantum information to thermalization, from gravity to elasticity. In the context of hydrodynamics it has been shown theoretically, and confirmed experimentally, that such restricted mobility leads to novel emergent scaling laws. In this talk, I will introduce a framework to describe the hydrodynamics of fractons and predict such scaling laws, with particular focus on systems with conserved dipole and momentum. This hydrodynamics turns out to have rather exotic properties, owing to the fact that dipole conservation leads to a non-trivial extension of spacetime symmetries. After developing an effective theory approach that allows accounting for fluctuations, I will show that such theory contains relevant nonlinearities that lead to the emergence of stochastic non-Gaussian universality classes, even in three spatial dimensions, thus constituting a breakdown of its local hydrodynamic description.
Posted by: andrea
Mon
17 Oct 2022
LonTI: Lectures on the duality between the Sine-Gordon and the Thirring model
Alessandro Torrielli
(University of Surrey)
Abstract:
We will describe the duality between two integrable systems: the 2D Sine-Gordon model and the 2D Thirring model. We will spend some time describing the classical and quantum Sine-Gordon model, in particular its spectrum, S-matrices and underlying quantum-group symmetry. We will then present the duality with the Thirring model as originally stated by Coleman and refined in subsequent literature. All the basic elements will be provided without relying on too many pre-requisites beyond standard graduate-level quantum field theory. The notes comprise a series of exercises.
We will describe the duality between two integrable systems: the 2D Sine-Gordon model and the 2D Thirring model. We will spend some time describing the classical and quantum Sine-Gordon model, in particular its spectrum, S-matrices and underlying quantum-group symmetry. We will then present the duality with the Thirring model as originally stated by Coleman and refined in subsequent literature. All the basic elements will be provided without relying on too many pre-requisites beyond standard graduate-level quantum field theory. The notes comprise a series of exercises.
Posted by: lonti
Wed
12 Oct 2022
Estimating global symmetry violating amplitudes using wormholes
Juan Maldacena
(Institute for Advanced Study)
Abstract:
We know that quantum gravity is expected to violate global symmetries of
effective gravity theories. Black holes are expected to play a role in
this violation. We discuss computations of gravity amplitudes, mainly
involving scattering of spherically symmetric shells, that violate
global symmetries. We will review prior work in two dimensions and we
will discuss the new features that arise in higher dimensions.
We know that quantum gravity is expected to violate global symmetries of
effective gravity theories. Black holes are expected to play a role in
this violation. We discuss computations of gravity amplitudes, mainly
involving scattering of spherically symmetric shells, that violate
global symmetries. We will review prior work in two dimensions and we
will discuss the new features that arise in higher dimensions.
Posted by: CityU2
Wed
12 Oct 2022
Where do we live in the string landscape?
Irene Valenzuela
(CERN)
Abstract:
In this talk, I will discuss the possibility that our universe lies near the boundary of the field space in string theory, including the theoretical challenges and the exciting phenomenological implications. These boundaries share some universal properties imposed by quantum gravity (sometimes promoted to Swampland constraints) that resemble our universe, like weak couplings, approximate global symmetries or small (time-dependent) vacuum energy. However, it remains as an open challenge to get an accelerated cosmology. We study whether the runaway behaviour of stringy scalar potentials towards in finite distance can produce an accelerated expanding cosmology a la quintessence, finding some potential examples in F-theory flux compactifications. I will discuss the caveats of these examples and the comparison to Swampland bounds. Furthermore, a universal feature of these regions is that there is a light infinite tower of states which is correlated to the value of the vacuum energy. I will show how experimental constraints force this tower to correspond to a KK tower (of mass of order neutrino scale) of a single extra mesoscopic dimension of order 10^{-6) m, which we denote as the Dark Dimension.
In this talk, I will discuss the possibility that our universe lies near the boundary of the field space in string theory, including the theoretical challenges and the exciting phenomenological implications. These boundaries share some universal properties imposed by quantum gravity (sometimes promoted to Swampland constraints) that resemble our universe, like weak couplings, approximate global symmetries or small (time-dependent) vacuum energy. However, it remains as an open challenge to get an accelerated cosmology. We study whether the runaway behaviour of stringy scalar potentials towards in finite distance can produce an accelerated expanding cosmology a la quintessence, finding some potential examples in F-theory flux compactifications. I will discuss the caveats of these examples and the comparison to Swampland bounds. Furthermore, a universal feature of these regions is that there is a light infinite tower of states which is correlated to the value of the vacuum energy. I will show how experimental constraints force this tower to correspond to a KK tower (of mass of order neutrino scale) of a single extra mesoscopic dimension of order 10^{-6) m, which we denote as the Dark Dimension.
Posted by: CityU2
Tue
11 Oct 2022
Chiral approach to massive higher spins
Alexander Ochirov
(University of Oxford)
Abstract:
Quantum field theory of higher-spin particles is a formidable subject, where Lorentz-invariant approaches tend to lead to a rich gauge-symmetry structure, which serves to preserve the physical number of degrees of freedom. Introducing consistent interactions in such approaches is a non-trivial task, with most higher-spin Lagrangians specified only up to three points. In this talk, I will discuss a new, chiral description for massive higher-spin particles, which in four spacetime dimensions allows to do away with this kind of gauge symmetry. This greatly facilitates the introduction of consistent interactions. I will concentrate on three theories, in which higher-spin matter is coupled to electrodynamics, non-Abelian gauge theory or gravity. These theories are currently the only examples of consistent interacting field theories with massive higher-spin fields. The presented theories are chiral and have simple Lagrangians, resulting in Feynman rules analogous to those of massive scalars. In particular, I will discuss the resulting tree-level scattering amplitudes with two higher-spin matter particles and any number of positive-helicity photons, gluons or gravitons. These amplitudes were previously computed via on-shell recursion and provided evidence for the existence of such simple massive higher-spin theories.
Quantum field theory of higher-spin particles is a formidable subject, where Lorentz-invariant approaches tend to lead to a rich gauge-symmetry structure, which serves to preserve the physical number of degrees of freedom. Introducing consistent interactions in such approaches is a non-trivial task, with most higher-spin Lagrangians specified only up to three points. In this talk, I will discuss a new, chiral description for massive higher-spin particles, which in four spacetime dimensions allows to do away with this kind of gauge symmetry. This greatly facilitates the introduction of consistent interactions. I will concentrate on three theories, in which higher-spin matter is coupled to electrodynamics, non-Abelian gauge theory or gravity. These theories are currently the only examples of consistent interacting field theories with massive higher-spin fields. The presented theories are chiral and have simple Lagrangians, resulting in Feynman rules analogous to those of massive scalars. In particular, I will discuss the resulting tree-level scattering amplitudes with two higher-spin matter particles and any number of positive-helicity photons, gluons or gravitons. These amplitudes were previously computed via on-shell recursion and provided evidence for the existence of such simple massive higher-spin theories.
Posted by: IC
Thu
6 Oct 2022
From Amplitudes to Cosmology
๐ London
Arthur Lipstein
(Durham)
Abstract:
Whereas scattering amplitudes probe physics at the shortest distances, cosmology probes physics at the largest scales. Nevertheless, many concepts discovered in the study of scattering amplitudes have an analogue for cosmological observables. In this talk I will describe some aspects of this program which I have recently been investigating such as the double copy, scattering equations, and soft limits, and will discuss how these directions are interrelated.
Whereas scattering amplitudes probe physics at the shortest distances, cosmology probes physics at the largest scales. Nevertheless, many concepts discovered in the study of scattering amplitudes have an analogue for cosmological observables. In this talk I will describe some aspects of this program which I have recently been investigating such as the double copy, scattering equations, and soft limits, and will discuss how these directions are interrelated.
Posted by: QMW
Wed
5 Oct 2022
Chiral symmetry and mass shift for the lattice Schwinger model
๐ London
Bernardo Zan
(Princeton)
Abstract:
The Schwinger model is one of the simplest gauge theories, yet it is only solvable in the massless case. In order to obtain numerical results, the Kogut-Susskind lattice approach with staggered fermions is regularly used. I will show that, contrary to what it was believed, the lattice mass and the continuum mass are actually not the same, but they are related by a mass shift. This can be understood by considering the (anomalous) chiral symmetry in the massless case, and has the advantage of greatly improving convergence of the numerics. I will comment on the charge-q Schwinger model as well as the multiflavor Schwinger model.
The Schwinger model is one of the simplest gauge theories, yet it is only solvable in the massless case. In order to obtain numerical results, the Kogut-Susskind lattice approach with staggered fermions is regularly used. I will show that, contrary to what it was believed, the lattice mass and the continuum mass are actually not the same, but they are related by a mass shift. This can be understood by considering the (anomalous) chiral symmetry in the massless case, and has the advantage of greatly improving convergence of the numerics. I will comment on the charge-q Schwinger model as well as the multiflavor Schwinger model.
Posted by: andrea
Tue
4 Oct 2022
Higher-derivative corrections to the entropy of supersymmetric AdS_5 black holes and their holographic match
Davide Cassani
(University of Padua)
Abstract:
The fundamental theory of quantum gravity is expected to manifest itself at low energies via a series of higher-derivative corrections to Einsteinรขโฌโขs theory. Holography and supersymmetry are of great help to characterize such corrections in controlled scenarios: through holography, quantum gravity in Anti de Sitter (AdS) space has a rigorous definition in terms of a conformal field theory (CFT), while supersymmetry makes it possible to compute exact observables and make quantitative predictions. In this context, we will illustrate how a CFT generating function known as the superconformal index provides a microscopic explanation of the entropy of five-dimensional supersymmetric black holes in AdS. We will show how this match goes beyond the leading Bekenstein-Hawking term and includes higher-derivative corrections.
The fundamental theory of quantum gravity is expected to manifest itself at low energies via a series of higher-derivative corrections to Einsteinรขโฌโขs theory. Holography and supersymmetry are of great help to characterize such corrections in controlled scenarios: through holography, quantum gravity in Anti de Sitter (AdS) space has a rigorous definition in terms of a conformal field theory (CFT), while supersymmetry makes it possible to compute exact observables and make quantitative predictions. In this context, we will illustrate how a CFT generating function known as the superconformal index provides a microscopic explanation of the entropy of five-dimensional supersymmetric black holes in AdS. We will show how this match goes beyond the leading Bekenstein-Hawking term and includes higher-derivative corrections.
Posted by: IC
September 2022
Wed
28 Sep 2022
Multipoint Lightcone Bootstrap from Conformal Block Integrability
๐ London
Jeremy Mann
(KCL)
Abstract:
In conformal field theory, the lightcone bootstrap is an analytic approach to solving the crossing equations of correlation functions. The blocks, namely the kinematical constituents of a crossing equation, must be computed near lightcone singularities and resumed. At four points, this culminates in the universal dynamics of a double-twist operator at large spin. While extensions to higher points have been recently studied, further progress has been hampered by our limited knowledge of the blocks. In this talk, I will review the first applications of conformal block integrability to the multipoint lightcone bootstrap, focusing on scalar five point functions for concrete expressions. First, starting from a Gaudin model, I will review the construction of an integrable system that determines blocks via differential equations and a boundary condition. These differential equations, and by extension the crossing equations, can be explicitly solved in lightcone limits. Finally, after summarizing the old and new results we obtain at five points, I will comment on what this may entail for universal triple-twist data in six point functions. This is based on my thesis work, as well as an upcoming paper with Lorenzo Quintavalle, Apratim Kaviraj and Volker Schomerus.
In conformal field theory, the lightcone bootstrap is an analytic approach to solving the crossing equations of correlation functions. The blocks, namely the kinematical constituents of a crossing equation, must be computed near lightcone singularities and resumed. At four points, this culminates in the universal dynamics of a double-twist operator at large spin. While extensions to higher points have been recently studied, further progress has been hampered by our limited knowledge of the blocks. In this talk, I will review the first applications of conformal block integrability to the multipoint lightcone bootstrap, focusing on scalar five point functions for concrete expressions. First, starting from a Gaudin model, I will review the construction of an integrable system that determines blocks via differential equations and a boundary condition. These differential equations, and by extension the crossing equations, can be explicitly solved in lightcone limits. Finally, after summarizing the old and new results we obtain at five points, I will comment on what this may entail for universal triple-twist data in six point functions. This is based on my thesis work, as well as an upcoming paper with Lorenzo Quintavalle, Apratim Kaviraj and Volker Schomerus.
Posted by: andrea