Triangle Seminars
December 2020
Thu
17 Dec 2020
Integrability Gong Show
seven speakers
Abstract:
We will have seven 10 mins talks + discussions, with:
1) Sara Bonansea (INFN Florence and NBI) - "Wilson loop correlators in defect N=4 SYM"
2) Andrea Fontanella (Humboldt) - "Lie Algebra Expansion in Coset Sigma Models and Non-relativistic String Theory"
3) Suvajit Majumder (City) - "Protected states in AdS3xS3xT4 from integrability"
4) Gerben Oling (NBI) - "Non-relativistic strings and limits of AdS/CFT"
5) Chiara Paletta (TCD) - "Integrable open quantum systems"
6) Davide Polvara (Durham) - "From tree-level perturbation theory to the S-matrix bootstrap in two dimensions"
7) Anton Pribytok (TCD) - "Deformed AdS Integrability and Free Fermion Condition"
–––––––––––––––––- Part of the London Integrability Journal Club. New participants are required to register using the form at integrability-london.weebly.com. The link will be emailed. Abstracts on the website.
We will have seven 10 mins talks + discussions, with:
1) Sara Bonansea (INFN Florence and NBI) - "Wilson loop correlators in defect N=4 SYM"
2) Andrea Fontanella (Humboldt) - "Lie Algebra Expansion in Coset Sigma Models and Non-relativistic String Theory"
3) Suvajit Majumder (City) - "Protected states in AdS3xS3xT4 from integrability"
4) Gerben Oling (NBI) - "Non-relativistic strings and limits of AdS/CFT"
5) Chiara Paletta (TCD) - "Integrable open quantum systems"
6) Davide Polvara (Durham) - "From tree-level perturbation theory to the S-matrix bootstrap in two dimensions"
7) Anton Pribytok (TCD) - "Deformed AdS Integrability and Free Fermion Condition"
–––––––––––––––––- Part of the London Integrability Journal Club. New participants are required to register using the form at integrability-london.weebly.com. The link will be emailed. Abstracts on the website.
Posted by: andrea
Wed
16 Dec 2020
Holography of class F field theories
Morteza Hosseini
(Kavli IPMU)
Abstract:
I will perform a consistent reduction of 6d matter-coupled F(4) gauged supergravity on a compact Riemann surface of genus g, at the level of the bosonic fields. The result is an N=2 gauged supergravity coupled to two vector multiplets and a single hypermultiplet. The four-dimensional model is holographically dual to the 3d superconformal field theories of class F, describing different brane systems in massive type IIA and IIB wrapped on the Riemann Surface. I will then use the results to find the first examples of dyonic static black holes of class F and perform a microscopic counting of their entropy via the 5d topologically twisted index. I will also find new asymptotically AdS solutions, including rotating black holes, in the subtruncations of the 4d model, providing predictions for the squashed S^3 partition functions and the superconformal and refined twisted indices of class F field theories.
Join Zoom Meeting
https://zoom.us/j/92805841030?pwd=dTVGQ2h5ZUw4cndKd3JUYTNYVTMrdz09
Meeting ID: 928 0584 1030
Passcode: 902526
I will perform a consistent reduction of 6d matter-coupled F(4) gauged supergravity on a compact Riemann surface of genus g, at the level of the bosonic fields. The result is an N=2 gauged supergravity coupled to two vector multiplets and a single hypermultiplet. The four-dimensional model is holographically dual to the 3d superconformal field theories of class F, describing different brane systems in massive type IIA and IIB wrapped on the Riemann Surface. I will then use the results to find the first examples of dyonic static black holes of class F and perform a microscopic counting of their entropy via the 5d topologically twisted index. I will also find new asymptotically AdS solutions, including rotating black holes, in the subtruncations of the 4d model, providing predictions for the squashed S^3 partition functions and the superconformal and refined twisted indices of class F field theories.
Join Zoom Meeting
https://zoom.us/j/92805841030?pwd=dTVGQ2h5ZUw4cndKd3JUYTNYVTMrdz09
Meeting ID: 928 0584 1030
Passcode: 902526
Posted by: IC
Wed
16 Dec 2020
Hamiltonian truncation in AdS
๐ London
Marco Meineri
(CERN)
Abstract:
We study quantum field theory in AdS_2 within the framework of Hamiltonian truncation. We start from a solvable theory and we deform the Hamiltonian with an interaction term. We find the spectrum as a function of the coupling, and we aim at connecting the solvable regime with the strongly coupled flat space physics. Hamiltonian truncation in infinite volume presents specific challenges, and special care is needed to recover the physical energy gaps as the cutoff is removed. To this end, we propose a general prescription, we give an argument for its validity and we check it in various examples.
[For the link to the Zoom room, please email alejandro.cabo_bizet@kcl.ac.uk].
We study quantum field theory in AdS_2 within the framework of Hamiltonian truncation. We start from a solvable theory and we deform the Hamiltonian with an interaction term. We find the spectrum as a function of the coupling, and we aim at connecting the solvable regime with the strongly coupled flat space physics. Hamiltonian truncation in infinite volume presents specific challenges, and special care is needed to recover the physical energy gaps as the cutoff is removed. To this end, we propose a general prescription, we give an argument for its validity and we check it in various examples.
[For the link to the Zoom room, please email alejandro.cabo_bizet@kcl.ac.uk].
Posted by: andrea
Tue
15 Dec 2020
tba
Frederik M. Denef
(Columbia University)
Abstract:
tba
[please email a.held@imperial.ac.uk for zoom link or password]
tba
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
10 Dec 2020
An Operator Product Expansion for Form Factors
Matthias Wilhelm
(Niels Bohr Institute Copenhagen)
Abstract:
In this talk, I discuss an operator product expansion for planar form factors of local operators in N=4 SYM theory. In this expansion, a form factor is decomposed into a sequence of known pentagon transitions and a new universal object - the form factor transition. This transition is subject to a set of non-trivial bootstrap constraints, which can be used to determine it at finite coupling. I demonstrate this for MHV form factors of the chiral half of the stress tensor supermultiplet, which in particular contains the chiral Lagrangian and the 20'. –– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
In this talk, I discuss an operator product expansion for planar form factors of local operators in N=4 SYM theory. In this expansion, a form factor is decomposed into a sequence of known pentagon transitions and a new universal object - the form factor transition. This transition is subject to a set of non-trivial bootstrap constraints, which can be used to determine it at finite coupling. I demonstrate this for MHV form factors of the chiral half of the stress tensor supermultiplet, which in particular contains the chiral Lagrangian and the 20'. –– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
9 Dec 2020
An N=1 Lagrangian for an N=3 SCFT
๐ London
Gabi Zafrir
(Milan Bicocca U.)
Abstract:
Purely N=3 SCFTs are naturally strongly coupled, and
expected to not have a Lagrangian description manifesting their N=3
supersymmetry. However, these may be reached through a deformation of
a theory preserving less supersymmetry. We shall present a strategy to
try to conjecture such models, and exemplify it by presenting an N=1
model conjectured to flow to an N=3 SCFT, deformed by a marginal
deformation. We shall also discuss and exemplify how such proposals
can be tested.
[For the Zoom link please email to alejandro.cabo_bizet@kcl.ac.uk]
Purely N=3 SCFTs are naturally strongly coupled, and
expected to not have a Lagrangian description manifesting their N=3
supersymmetry. However, these may be reached through a deformation of
a theory preserving less supersymmetry. We shall present a strategy to
try to conjecture such models, and exemplify it by presenting an N=1
model conjectured to flow to an N=3 SCFT, deformed by a marginal
deformation. We shall also discuss and exemplify how such proposals
can be tested.
[For the Zoom link please email to alejandro.cabo_bizet@kcl.ac.uk]
Posted by: andrea
Wed
9 Dec 2020
High energy scattering of highly excited strings
Vladimir Rosenhaus
(IAS)
Abstract:
The n-point tachyon amplitude is a classic and well-known result in bosonic string theory. Rather than studying tachyon amplitudes, we will compute scattering amplitudes involving highly excited string states. Along the way we review and elaborate on the DDF construction of string vertex operators, and describe properties of a generic excited string. Based on work in progress with D. Gross.
The n-point tachyon amplitude is a classic and well-known result in bosonic string theory. Rather than studying tachyon amplitudes, we will compute scattering amplitudes involving highly excited string states. Along the way we review and elaborate on the DDF construction of string vertex operators, and describe properties of a generic excited string. Based on work in progress with D. Gross.
Posted by: IC
Tue
8 Dec 2020
Volume preserving diffeomorphism as a higher-rank gauge symmetry
Dam Thanh Son
(Univerity of Chicago)
Abstract:
Recently, theories with higher rank gauge symmetries are drawing attention in condensed matter physics. Such theories are thought to be related to the so-called "fractons," quasiparticles with limited mobility that appear in some lattice models. We show that one version of such higher ranked symmetry can be "nonlinearlized" into volume-preserving diffeomorphism. We demonstrate that several condensed matter systems, including the fractional quantum Hall effect and ferromagnetism, secretly possess this symmetry, which sheds another light to some peculiar features of the quasiparticles in these systems.
[please email a.held@imperial.ac.uk for zoom link or password]
Recently, theories with higher rank gauge symmetries are drawing attention in condensed matter physics. Such theories are thought to be related to the so-called "fractons," quasiparticles with limited mobility that appear in some lattice models. We show that one version of such higher ranked symmetry can be "nonlinearlized" into volume-preserving diffeomorphism. We demonstrate that several condensed matter systems, including the fractional quantum Hall effect and ferromagnetism, secretly possess this symmetry, which sheds another light to some peculiar features of the quasiparticles in these systems.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
7 Dec 2020
Lonti 2020 : D Branes and Boundary States
Bogdan Stefanski
(City)
Abstract:
This is the live session included as part of the LonTI lecture on Conformal blocks in two dimensions. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. D-branes are a remarkable set of soliton-like objects in string theory which have played a critical role in many areas of string theory. Despite being non-perturbative, they can be understood exactly using world-sheet methods through the boundary state formalism. In this lecture, I introduce the notion of a boundary state and show how to use it to extract physical information about D-branes and the open strings that live on them.
This is the live session included as part of the LonTI lecture on Conformal blocks in two dimensions. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. D-branes are a remarkable set of soliton-like objects in string theory which have played a critical role in many areas of string theory. Despite being non-perturbative, they can be understood exactly using world-sheet methods through the boundary state formalism. In this lecture, I introduce the notion of a boundary state and show how to use it to extract physical information about D-branes and the open strings that live on them.
Posted by: pethybridge
Thu
3 Dec 2020
Topologically Ordered Matter and Why You Should be Interested
Steven Simon
(Oxford)
Abstract:
Abstract: In two dimensional topologically ordered matter, processes depend on gross topology rather than detailed geometry. Thinking in 2+1 dimensions, particle world lines can be interpreted as knots or links, and the amplitude for certain processes becomes a topological invariant of that link. While sounding rather exotic, we believe that such phases of matter not only exist, but have actually been observed in quantum Hall experiments, and could provide a route to building a quantum computer. Possibilities have also been proposed for creating similar physics in systems ranging from superfluid helium to topological superconductors to semiconductor-superconductor junctions to quantum wires to spin systems to graphene to cold atoms.
Please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk for the zoom link.
Abstract: In two dimensional topologically ordered matter, processes depend on gross topology rather than detailed geometry. Thinking in 2+1 dimensions, particle world lines can be interpreted as knots or links, and the amplitude for certain processes becomes a topological invariant of that link. While sounding rather exotic, we believe that such phases of matter not only exist, but have actually been observed in quantum Hall experiments, and could provide a route to building a quantum computer. Possibilities have also been proposed for creating similar physics in systems ranging from superfluid helium to topological superconductors to semiconductor-superconductor junctions to quantum wires to spin systems to graphene to cold atoms.
Please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk for the zoom link.
Posted by: QMW
Thu
3 Dec 2020
TBA
Costas Bachas
(Ecole Normale Superieure)
Thu
3 Dec 2020
Phases of unitary matrix models and lattice QCD in two dimensions
Jorge Russo
(University of Barcelona)
Abstract:
We investigate the different large N phases of a deformed Gross-Witten-Wadia U(N) matrix model.
The deformation, which leads to a solvable model, corresponds to the addition of characteristic polynomial insertions and mimicks the one-loop determinant of fermion matter. In one version of the model, the GWW phase transition is smoothed out and it becomes a crossover. In another version, the phase transition occurs along a critical line in the two-dimensional parameter space spanned by the 't~Hooft coupling \(\lambda \) and the Veneziano parameter \(\tau \). A calculation of the \(\beta \) function shows the existence of an IR stable fixed point. –– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
We investigate the different large N phases of a deformed Gross-Witten-Wadia U(N) matrix model.
The deformation, which leads to a solvable model, corresponds to the addition of characteristic polynomial insertions and mimicks the one-loop determinant of fermion matter. In one version of the model, the GWW phase transition is smoothed out and it becomes a crossover. In another version, the phase transition occurs along a critical line in the two-dimensional parameter space spanned by the 't~Hooft coupling \(\lambda \) and the Veneziano parameter \(\tau \). A calculation of the \(\beta \) function shows the existence of an IR stable fixed point. –– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
2 Dec 2020
A novel twistor string theory
Kevin Costello
(Perimeter Institute)
Abstract:
This seminar will be held over Zoom. The link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk for link.
I will report on some work in progress on type I topological strings on twistor space, and their relationship with integrable but non-supersymmetric field theories in three and four dimensions. This is closely related to recent work of Bittleston and Skinner.
This seminar will be held over Zoom. The link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk for link.
I will report on some work in progress on type I topological strings on twistor space, and their relationship with integrable but non-supersymmetric field theories in three and four dimensions. This is closely related to recent work of Bittleston and Skinner.
Posted by: CityU2
Wed
2 Dec 2020
Numerical CY metrics from holomorphic networks
Michael Douglas
(Simons Center for Geometry and Physics)
Abstract:
This seminar will be held over Zoom. The link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk for link.
We propose machine learning inspired methods for computing
numerical Calabi-Yau metrics, and implement them using Tensorflow/Keras. We compare them with previous work, and find that they are far more accurate for manifolds with little or no symmetry. We also discuss issues such as optimization methods, overparameterization and computational complexity. Joint work with Subramanian Lakshminarasimhan and Yidi Qi.
This seminar will be held over Zoom. The link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk for link.
We propose machine learning inspired methods for computing
numerical Calabi-Yau metrics, and implement them using Tensorflow/Keras. We compare them with previous work, and find that they are far more accurate for manifolds with little or no symmetry. We also discuss issues such as optimization methods, overparameterization and computational complexity. Joint work with Subramanian Lakshminarasimhan and Yidi Qi.
Posted by: CityU2
Tue
1 Dec 2020
Smashing Solitons of Cosmology
Mustafa Amin
(Rice University, Houston, Texas)
Abstract:
Long-lived, spatially-localized and coherently oscillating field configurations (pseudo-solitons, for example, axion stars and oscillons) can form naturally in cosmologically relevant axion-like fields constituting dark matter today or in fields at the end of inflation. When these clumps collide and merge, they can give rise to bursts of electromagnetic and gravitational waves. In this talk, I will first discuss earlier work on soliton formation mechanisms and their interactions, as well as gravitational wave production. Then, for the main part of the talk, I will focus on the production of potentially detectable electromagnetic bursts resulting from the merger of dense scalar field oscillons/axion stars in the current universe [this is based on our recent paper, https://arxiv.org/abs/2009.11337]. Time permitting, I will also discuss possible connections to Fast Radio Bursts.
[please email a.held@imperial.ac.uk for zoom link or password]
Long-lived, spatially-localized and coherently oscillating field configurations (pseudo-solitons, for example, axion stars and oscillons) can form naturally in cosmologically relevant axion-like fields constituting dark matter today or in fields at the end of inflation. When these clumps collide and merge, they can give rise to bursts of electromagnetic and gravitational waves. In this talk, I will first discuss earlier work on soliton formation mechanisms and their interactions, as well as gravitational wave production. Then, for the main part of the talk, I will focus on the production of potentially detectable electromagnetic bursts resulting from the merger of dense scalar field oscillons/axion stars in the current universe [this is based on our recent paper, https://arxiv.org/abs/2009.11337]. Time permitting, I will also discuss possible connections to Fast Radio Bursts.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
November 2020
Mon
30 Nov 2020
Lonti: Conformal blocks in two dimensions
๐ London
Gerard Watts
(KCL)
Abstract:
This is the live session included as part of the LonTI lecture on Conformal blocks in two dimensions. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.รขโฌโนรขโฌโนConformal blocks are the building blocks of conformal field theories, the key ingredients of correlation functions and knowledge of these blocks is central to the conformal bootstrap. This lecture covers some general results before quickly specialising to two-dimensions. It discusses the implications of global conformal invariance and then the larger and more constraining Virasoro algebra symmetry. It introduces various methods of calculation including brute force, differential equations, recursion relations and closed formulae - and some aspects of bootstrap techniques.
This is the live session included as part of the LonTI lecture on Conformal blocks in two dimensions. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.รขโฌโนรขโฌโนConformal blocks are the building blocks of conformal field theories, the key ingredients of correlation functions and knowledge of these blocks is central to the conformal bootstrap. This lecture covers some general results before quickly specialising to two-dimensions. It discusses the implications of global conformal invariance and then the larger and more constraining Virasoro algebra symmetry. It introduces various methods of calculation including brute force, differential equations, recursion relations and closed formulae - and some aspects of bootstrap techniques.
Posted by: pethybridge
Mon
30 Nov 2020
LonTI 2020: D-branes and boundary states
Bogdan Stefanski
(City)
Abstract:
D-branes are a remarkable set of soliton-like objects in string theory which have played a critical role in many areas of string theory. Despite being non-perturbative, they can be understood exactly using world-sheet methods through the boundary state formalism. In this lecture, I introduce the notion of a boundary state and show how to use it to extract physical information about D-branes and the open strings that live on them.
D-branes are a remarkable set of soliton-like objects in string theory which have played a critical role in many areas of string theory. Despite being non-perturbative, they can be understood exactly using world-sheet methods through the boundary state formalism. In this lecture, I introduce the notion of a boundary state and show how to use it to extract physical information about D-branes and the open strings that live on them.
Posted by: pethybridge
Thu
26 Nov 2020
Precision AdS /CFT
Paul Heslop
(Durham University)
Abstract:
For zoom link please email s.nagyATqmul.ac.uk
There will be a pre-seminar for students at 13:30.
Abstract: I will discuss 2 recent results arising out of the recent resurgence in concrete tests / predictions of AdS/CFT over the last few years. The first is the precise identification of the CFT operators dual to single particle supergravity states (based on 2007.095395) and the second is a forthcoming work explicitly relating four-point correlators to a string effective action on AdSxS.
For zoom link please email s.nagyATqmul.ac.uk
There will be a pre-seminar for students at 13:30.
Abstract: I will discuss 2 recent results arising out of the recent resurgence in concrete tests / predictions of AdS/CFT over the last few years. The first is the precise identification of the CFT operators dual to single particle supergravity states (based on 2007.095395) and the second is a forthcoming work explicitly relating four-point correlators to a string effective action on AdSxS.
Posted by: QMW
Thu
26 Nov 2020
Integrability Gong Show
six speakers
( )
Abstract:
This Thursday we will have six speakers presenting a 10 mins talk each.
1) Stefano Baiguera (Niels Bohr Institute), "Non-relativistic near-BPS corners of N=4 super Yang-Mills with SU(1,1) symmetry".
2) Ilija Buric (Desy), "From Integrable Gaudin Models to Multipoint Conformal Blocks",
3) Julius Julius (King's College London), "Baxter Equation for Boundary Integrability",
4) Rob Klabbers (Nordita), "How coordinate Bethe ansatz works for Inozemtsev model",
5) Yuan Miao (University of Amsterdam), "On the Q-operator and the spectrum of the XXZ model at root of unity".
6) Anne Spiering (Trinity College Dublin), "Integrability and Quantum Chaos in N=4 SYM from the Spectral Rigidity".
Join us to hear the latest news in integrability!
Important: Please make sure your Zoom version is updated, in order to use the break-out rooms feature for discussions after the talks. See the journal club website for abstracts of the talks.
––––––––––––––- Part of the London Integrability Journal Club. New participants please register using the form which can be found on the webpage integrability-london.weebly.com. The link will be emailed.
This Thursday we will have six speakers presenting a 10 mins talk each.
1) Stefano Baiguera (Niels Bohr Institute), "Non-relativistic near-BPS corners of N=4 super Yang-Mills with SU(1,1) symmetry".
2) Ilija Buric (Desy), "From Integrable Gaudin Models to Multipoint Conformal Blocks",
3) Julius Julius (King's College London), "Baxter Equation for Boundary Integrability",
4) Rob Klabbers (Nordita), "How coordinate Bethe ansatz works for Inozemtsev model",
5) Yuan Miao (University of Amsterdam), "On the Q-operator and the spectrum of the XXZ model at root of unity".
6) Anne Spiering (Trinity College Dublin), "Integrability and Quantum Chaos in N=4 SYM from the Spectral Rigidity".
Join us to hear the latest news in integrability!
Important: Please make sure your Zoom version is updated, in order to use the break-out rooms feature for discussions after the talks. See the journal club website for abstracts of the talks.
––––––––––––––- Part of the London Integrability Journal Club. New participants please register using the form which can be found on the webpage integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
25 Nov 2020
Multilegs, Superfluids and Semiclassics
๐ London
Riccardo Rattazzi
(EPFL)
Abstract:
Even in weakly coupled QFTs, perturbation theory breaks down
when one considers amplitudes with a large number \(n\) of legs. The series cleverly organizes as a double expansion in \(g^2\) and \(g^2n\).
I show how the series in \(g^2n\) can be fully captured by a semiclassical expansion around a non-trivial solution. Focussing on \(U(1)\) symmetric \(|\phi|^4\) theory in \(4\) and \(4-\epsilon\) dimension, I derive explicit and consistent all order results for the anomalous dimension of the complex operator \(\phi^n\). When restricting to the Wilson-Fisher fixed point and working on the cylinder, the dominant trajectory is seen to correspond to a superfluid phase for the conserved U(1). This creates a correspondence between, on one side, the spectrum of operators and fusion coefficients and and on the other the spectrum of hydrodynamics modes and their interactions. The results also nicely match Monte Carlo simulations in 3D, compatibly with the stunt of taking \(\epsilon=1\).
[please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
Even in weakly coupled QFTs, perturbation theory breaks down
when one considers amplitudes with a large number \(n\) of legs. The series cleverly organizes as a double expansion in \(g^2\) and \(g^2n\).
I show how the series in \(g^2n\) can be fully captured by a semiclassical expansion around a non-trivial solution. Focussing on \(U(1)\) symmetric \(|\phi|^4\) theory in \(4\) and \(4-\epsilon\) dimension, I derive explicit and consistent all order results for the anomalous dimension of the complex operator \(\phi^n\). When restricting to the Wilson-Fisher fixed point and working on the cylinder, the dominant trajectory is seen to correspond to a superfluid phase for the conserved U(1). This creates a correspondence between, on one side, the spectrum of operators and fusion coefficients and and on the other the spectrum of hydrodynamics modes and their interactions. The results also nicely match Monte Carlo simulations in 3D, compatibly with the stunt of taking \(\epsilon=1\).
[please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
Posted by: andrea
Tue
24 Nov 2020
Free Energy from Replica Wormholes
Netta Engelhardt
(Massachusetts Institute of Technology)
Abstract:
Recent developments on the black hole information paradox have shown that Euclidean wormholes รขโฌโ so called รขโฌลreplica wormholesรขโฌโขรขโฌโข can dominate the von Neumann entropy as computed by a gravitational path integral, and that inclusion of these wormholes results in a unitary Page curve. This development raises some puzzles from the perspective of factorization, and has raised questions regarding what the gravitational path integral is computing. In this talk, I will focus on understanding the relationship between the gravitational path integral and the partition function via the gravitational free energy (more generally the generating functional). A proper computation of the free energy requires a replica trick distinct from the usual one used to compute the entropy. I will show that in JT gravity there is a regime where the free energy computed without replica wormholes is pathological. Interestingly, the inclusion of replica wormholes is not quite sufficient to resolve the pathology: an alternative analytic continuation is required. I will discuss the implications of this for various interpretations of the gravitational path integral (e.g. as computing an ensemble average) and also mention some parallels with spin glasses.
[please email a.held@imperial.ac.uk for zoom link or password]
Recent developments on the black hole information paradox have shown that Euclidean wormholes รขโฌโ so called รขโฌลreplica wormholesรขโฌโขรขโฌโข can dominate the von Neumann entropy as computed by a gravitational path integral, and that inclusion of these wormholes results in a unitary Page curve. This development raises some puzzles from the perspective of factorization, and has raised questions regarding what the gravitational path integral is computing. In this talk, I will focus on understanding the relationship between the gravitational path integral and the partition function via the gravitational free energy (more generally the generating functional). A proper computation of the free energy requires a replica trick distinct from the usual one used to compute the entropy. I will show that in JT gravity there is a regime where the free energy computed without replica wormholes is pathological. Interestingly, the inclusion of replica wormholes is not quite sufficient to resolve the pathology: an alternative analytic continuation is required. I will discuss the implications of this for various interpretations of the gravitational path integral (e.g. as computing an ensemble average) and also mention some parallels with spin glasses.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Tue
24 Nov 2020
An exact AdS/CFT duality
๐ London
Matthias Gaberdiel
(ETH Zurich)
Abstract:
The AdS/CFT correspondence relates string theory on an Anti de Sitter (AdS) background to a dual conformal field theory (CFT) living on the boundary of AdS. One promising strategy for how to prove the duality is to consider the `tensionless' limit of string theory in which the dual CFT becomes weakly coupled. For the case of string theory on AdS3 we have recently identified a solvable world-sheet description for this tensionless limit. This opens the way towards proving the AdS/CFT correspondence, at least for this specific set-up.
Please contact Dionysios Anninos (dionysios.anninos@kcl.ac.uk) for the zoom link.
The AdS/CFT correspondence relates string theory on an Anti de Sitter (AdS) background to a dual conformal field theory (CFT) living on the boundary of AdS. One promising strategy for how to prove the duality is to consider the `tensionless' limit of string theory in which the dual CFT becomes weakly coupled. For the case of string theory on AdS3 we have recently identified a solvable world-sheet description for this tensionless limit. This opens the way towards proving the AdS/CFT correspondence, at least for this specific set-up.
Please contact Dionysios Anninos (dionysios.anninos@kcl.ac.uk) for the zoom link.
Posted by: oxford
Mon
23 Nov 2020
Lonti 2020:Witten diagrams and the Mellin transform in AdS/CFT
Congkao Wen
(QMUL)
Abstract:
This is the live session included as part of the LonTI lecture on Witten diagrams and the Mellin transform in AdS/CFT. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.AdS/CFT duality (or more general holographic principle) represents a major advance in understanding quantum gravity, and provides powerful tools for studying strongly coupled quantum field theories. This talk will give a basic introduction to AdS/CFT duality, with the focus on the computation of Witten diagrams and their Mellin transform. Witten diagrams, which play the role of Feynman diagrams, provide the means for computing correlation functions in AdS/CFT. We will show that CFT correlation functions obtained from Witten diagrams have much simpler structures after Mellin transform. Correlators in Mellin space are very analogous to the flat-space scattering amplitudes, and they are often called Mellin amplitudes. We will demonstrate the ideas by studying a few non-trivial examples.
This is the live session included as part of the LonTI lecture on Witten diagrams and the Mellin transform in AdS/CFT. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.AdS/CFT duality (or more general holographic principle) represents a major advance in understanding quantum gravity, and provides powerful tools for studying strongly coupled quantum field theories. This talk will give a basic introduction to AdS/CFT duality, with the focus on the computation of Witten diagrams and their Mellin transform. Witten diagrams, which play the role of Feynman diagrams, provide the means for computing correlation functions in AdS/CFT. We will show that CFT correlation functions obtained from Witten diagrams have much simpler structures after Mellin transform. Correlators in Mellin space are very analogous to the flat-space scattering amplitudes, and they are often called Mellin amplitudes. We will demonstrate the ideas by studying a few non-trivial examples.
Posted by: pethybridge
Mon
23 Nov 2020
Lonti 2020: Conformal blocks in two dimensions
๐ London
Gerard Watts
(KCL)
Abstract:
รขโฌโนรขโฌโนConformal blocks are the building blocks of conformal field theories, the key ingredients of correlation functions and knowledge of these blocks is central to the conformal bootstrap. This lecture covers some general results before quickly specialising to two-dimensions. It discusses the implications of global conformal invariance and then the larger and more constraining Virasoro algebra symmetry. It introduces various methods of calculation including brute force, differential equations, recursion relations and closed formulae - and some aspects of bootstrap techniques.
รขโฌโนรขโฌโนConformal blocks are the building blocks of conformal field theories, the key ingredients of correlation functions and knowledge of these blocks is central to the conformal bootstrap. This lecture covers some general results before quickly specialising to two-dimensions. It discusses the implications of global conformal invariance and then the larger and more constraining Virasoro algebra symmetry. It introduces various methods of calculation including brute force, differential equations, recursion relations and closed formulae - and some aspects of bootstrap techniques.
Posted by: pethybridge
Thu
19 Nov 2020
Cutkosky Rules and Unitarity (Violation) in D-instanton Amplitudes
Ashoke Sen
(Harish-Chandra Research Institute)
Abstract:
In perturbative amplitudes in quantum field theory and string field theory, Cutkosky rule expresses the anti-hermitian part of a Feynman diagram in terms of sum over all its cut diagrams, and this in turn is used to prove unitarity of the theory. For D-instanton contribution to a string theory amplitude, the cutting rule needed for the proof of unitarity is somewhat different; we need to sum over only those cut diagrams for which all the world-sheet boundaries ending on some particular D instanton lie on the same side of the cut. By working with the closed string effective action, obtained after integrating out the open string modes, we prove that the D-instanton amplitudes actually satisfy these cutting rules, provided the effective action is real. The violation of unitarity in the closed string sector of two dimensional string theory can be traced to the failure of this reality condition. In the critical superstring theory, multi-instanton and multi anti-instanton amplitudes satisfy the reality condition. Contribution to the amplitudes from the instanton anti-instanton sector satisfies the reality condition if we make a specific choice of integration cycle over the configuration space of string fields, whereas contribution due to the non-BPS D-instantons will need to either vanish or have an overall real normalization in order for it to give real contribution.
(please email jung-wook.kim AT qmul.ac.uk for the zoom link)
In perturbative amplitudes in quantum field theory and string field theory, Cutkosky rule expresses the anti-hermitian part of a Feynman diagram in terms of sum over all its cut diagrams, and this in turn is used to prove unitarity of the theory. For D-instanton contribution to a string theory amplitude, the cutting rule needed for the proof of unitarity is somewhat different; we need to sum over only those cut diagrams for which all the world-sheet boundaries ending on some particular D instanton lie on the same side of the cut. By working with the closed string effective action, obtained after integrating out the open string modes, we prove that the D-instanton amplitudes actually satisfy these cutting rules, provided the effective action is real. The violation of unitarity in the closed string sector of two dimensional string theory can be traced to the failure of this reality condition. In the critical superstring theory, multi-instanton and multi anti-instanton amplitudes satisfy the reality condition. Contribution to the amplitudes from the instanton anti-instanton sector satisfies the reality condition if we make a specific choice of integration cycle over the configuration space of string fields, whereas contribution due to the non-BPS D-instantons will need to either vanish or have an overall real normalization in order for it to give real contribution.
(please email jung-wook.kim AT qmul.ac.uk for the zoom link)
Posted by: QMW
Thu
19 Nov 2020
From CFT to AdS for Higher-Spin amplitudes
Shailesh Lal
Abstract:
Higher-Spin/CFT dualities are a promising playground to unravel the nuts and bolts of the AdS/CFT correspondence
away from supersymmetry, as the bulk and boundary descriptions are simultaneously perturbative. In this talk we demonstrate
how the free CFT three-point correlator involving two scalars and one conserved current of arbitrary spin organizes itself into the
dual AdS amplitude. Techniques from the embedding space formalism for AdS and CFT, as well as an insightful variation of Schwinger
parametrization, proposed in hep-th/0308184 play an important role. The talk will be based on arXiv:2009.10110.
Join Zoom Meeting
https://zoom.us/j/3515880979?pwd=MWU0V1ZOUzJ1eUozL1Vkb1RtbTZhZz09
Meeting ID: 351 588 0979
Passcode: the T word in AdS/CFT
Higher-Spin/CFT dualities are a promising playground to unravel the nuts and bolts of the AdS/CFT correspondence
away from supersymmetry, as the bulk and boundary descriptions are simultaneously perturbative. In this talk we demonstrate
how the free CFT three-point correlator involving two scalars and one conserved current of arbitrary spin organizes itself into the
dual AdS amplitude. Techniques from the embedding space formalism for AdS and CFT, as well as an insightful variation of Schwinger
parametrization, proposed in hep-th/0308184 play an important role. The talk will be based on arXiv:2009.10110.
Join Zoom Meeting
https://zoom.us/j/3515880979?pwd=MWU0V1ZOUzJ1eUozL1Vkb1RtbTZhZz09
Meeting ID: 351 588 0979
Passcode: the T word in AdS/CFT
Posted by: IC
Thu
19 Nov 2020
Integrable Kondo line defect, 4D Chern Simons, and ODE/IM correspondence
Jingxiang Wu
(Perimeter Institute)
Abstract:
I will discuss the integrability and wall-crossing properties of Kondo line defects in rational conformal field theories. It provides a large class of interesting defect RG flow starting from topological line defects. As a surprise, I will discuss new examples of the ODE/IM correspondence and our attempts towards its physical origin using 4d Chern Simons theory. This work is part of a multi-pronged exploration of studying 4D Chern-Simons theory as an overarching structure for integrable systems. –– Part of London Integrability Journal Club. New participants can register using the form at integrability-london.weebly.com. The link will be emailed.
I will discuss the integrability and wall-crossing properties of Kondo line defects in rational conformal field theories. It provides a large class of interesting defect RG flow starting from topological line defects. As a surprise, I will discuss new examples of the ODE/IM correspondence and our attempts towards its physical origin using 4d Chern Simons theory. This work is part of a multi-pronged exploration of studying 4D Chern-Simons theory as an overarching structure for integrable systems. –– Part of London Integrability Journal Club. New participants can register using the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
18 Nov 2020
Universes as Bigdata: from Geometry, to Physics, to Machine-Learning
๐ London
Yang-Hui He
(City)
Abstract:
We briefly overview how historically string theory led theoretical physics first to algebraic/differential geometry, and then to computational geometry, and now to data science.
Using the Calabi-Yau landscape - accumulated by the collaboration of physicists, mathematicians and computer scientists over the last 4 decades - as a starting-point and concrete playground, we then launch to review our recent programme in machine-learning mathematical structures and address the tantalizing question of how AI helps doing mathematics, ranging from geometry, to representation theory, to combinatorics, to number theory.
Zoom Link: https://us02web.zoom.us/j/83496714171?pwd=bld3QmQ2c21laWxEWTd6ejVQbjZ5dz09 (contact dionysios.anninos@kcl.ac.uk for password)
We briefly overview how historically string theory led theoretical physics first to algebraic/differential geometry, and then to computational geometry, and now to data science.
Using the Calabi-Yau landscape - accumulated by the collaboration of physicists, mathematicians and computer scientists over the last 4 decades - as a starting-point and concrete playground, we then launch to review our recent programme in machine-learning mathematical structures and address the tantalizing question of how AI helps doing mathematics, ranging from geometry, to representation theory, to combinatorics, to number theory.
Zoom Link: https://us02web.zoom.us/j/83496714171?pwd=bld3QmQ2c21laWxEWTd6ejVQbjZ5dz09 (contact dionysios.anninos@kcl.ac.uk for password)
Posted by: oxford
Tue
17 Nov 2020
Maximally constraining dark energy
Johannes Noller
(Cambridge University, DAMPT)
Abstract:
In this talk I will sketch how we can test gravity with unprecedented precision by combining new gravitational wave measurements, observational bounds from cosmology, and novel particle theory inspired insights, in particular allowing us to zoom in on the nature of dark energy. In doing so, I will highlight the interplay between gravitational wave constraints on gravity post-GW170817, data constraints from cosmic microwave background and galaxy clustering measurements, and novel theoretical priors on such theories (ranging from purely classical stability requirements to radiative stability- and positivity-related priors).
[please email a.held@imperial.ac.uk for zoom link or password]
In this talk I will sketch how we can test gravity with unprecedented precision by combining new gravitational wave measurements, observational bounds from cosmology, and novel particle theory inspired insights, in particular allowing us to zoom in on the nature of dark energy. In doing so, I will highlight the interplay between gravitational wave constraints on gravity post-GW170817, data constraints from cosmic microwave background and galaxy clustering measurements, and novel theoretical priors on such theories (ranging from purely classical stability requirements to radiative stability- and positivity-related priors).
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
16 Nov 2020
Witten diagrams and the Mellin transform in AdS/CFT
Congkao Wen
(QMUL)
Abstract:
AdS/CFT duality (or more general holographic principle) represents a major advance in understanding quantum gravity, and provides powerful tools for studying strongly coupled quantum field theories. This talk will give a basic introduction to AdS/CFT duality, with the focus on the computation of Witten diagrams and their Mellin transform. Witten diagrams, which play the role of Feynman diagrams, provide the means for computing correlation functions in AdS/CFT. We will show that CFT correlation functions obtained from Witten diagrams have much simpler structures after Mellin transform. Correlators in Mellin space are very analogous to the flat-space scattering amplitudes, and they are often called Mellin amplitudes. We will demonstrate the ideas by studying a few non-trivial examples.
AdS/CFT duality (or more general holographic principle) represents a major advance in understanding quantum gravity, and provides powerful tools for studying strongly coupled quantum field theories. This talk will give a basic introduction to AdS/CFT duality, with the focus on the computation of Witten diagrams and their Mellin transform. Witten diagrams, which play the role of Feynman diagrams, provide the means for computing correlation functions in AdS/CFT. We will show that CFT correlation functions obtained from Witten diagrams have much simpler structures after Mellin transform. Correlators in Mellin space are very analogous to the flat-space scattering amplitudes, and they are often called Mellin amplitudes. We will demonstrate the ideas by studying a few non-trivial examples.
Posted by: pethybridge
Mon
16 Nov 2020
LonTI: Branes and the moduli space of instantons
Amihay Hanany
(IC)
Abstract:
This is the live session included as part of the LonTI lecture on Branes and the moduli space of instantons. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Instantons, or solutions to the self dual Yang Mills (SDYM) equations are well known solutions, introduced in the mid 70s and played a role in a host of applications in QFT and String Theory. This talk will show a simple brane construction which allows the computation of the moduli space of solutions to the SDYM equations, introduce the student to the world of quivers, and demonstrate simple computations which allow evaluations of these moduli spaces.
รขโฌโน
This is the live session included as part of the LonTI lecture on Branes and the moduli space of instantons. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Instantons, or solutions to the self dual Yang Mills (SDYM) equations are well known solutions, introduced in the mid 70s and played a role in a host of applications in QFT and String Theory. This talk will show a simple brane construction which allows the computation of the moduli space of solutions to the SDYM equations, introduce the student to the world of quivers, and demonstrate simple computations which allow evaluations of these moduli spaces.
รขโฌโน
Posted by: pethybridge
Sat
14 Nov 2020
t.b.a.
Paul Fendley
(Oxford)
Abstract:
t.b.a. –––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
t.b.a. –––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
Posted by: andrea
Thu
12 Nov 2020
Celestial Primaries and their Memories
Sabrina Pasterski
(Princeton)
Abstract:
(for Zoom link please email Silvia Nagy s.nagyATqmul.ac.uk There will be a pre-seminar for students at 13.30)
ABSTRACT:
A universal relationship between asymptotic symmetries, QFT soft theorems, and low energy observables has reinvigorated attempts at flat space holography. We will begin by introducing a map from 4d S-matrix elements to 2d correlators in a putative dual Celestial CFT, and then re-examine the IR triangle from the perspective of our Celestial CFT.
(for Zoom link please email Silvia Nagy s.nagyATqmul.ac.uk There will be a pre-seminar for students at 13.30)
ABSTRACT:
A universal relationship between asymptotic symmetries, QFT soft theorems, and low energy observables has reinvigorated attempts at flat space holography. We will begin by introducing a map from 4d S-matrix elements to 2d correlators in a putative dual Celestial CFT, and then re-examine the IR triangle from the perspective of our Celestial CFT.
Posted by: QMW
Thu
12 Nov 2020
Superintegrable systems on moduli spaces of flat connections
Nicolai Reshetikhin
(Berkeley)
Abstract:
Part of London Integrability Journal Club. New participants should register using the form at integrability-london.weebly.com. The link will be emailed.
Part of London Integrability Journal Club. New participants should register using the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
11 Nov 2020
The large charge expansion
๐ London
Susanne Reffert
(University of Bern)
Abstract:
In has become clear in recent years that working in sectors of large global charge of strongly coupled and otherwise inaccessible CFTs leads to important simplifications. It is indeed possible to formulate an effective action in which the large charge appears as a control parameter. In this talk, I will explain the basic notions of the large-charge expansion using the simple example of the O(2) model and then generalize to models with a richer structure which showcase other effects. [For the zoom link please email alejandro.cabo_bizet@kcl.ac.uk]
In has become clear in recent years that working in sectors of large global charge of strongly coupled and otherwise inaccessible CFTs leads to important simplifications. It is indeed possible to formulate an effective action in which the large charge appears as a control parameter. In this talk, I will explain the basic notions of the large-charge expansion using the simple example of the O(2) model and then generalize to models with a richer structure which showcase other effects. [For the zoom link please email alejandro.cabo_bizet@kcl.ac.uk]
Posted by: andrea
Tue
10 Nov 2020
Closed strings and weak gravity condition from higher-spin causality
Sandipan Kundu
(Johns Hopkins University)
Abstract:
I will show that metastable higher spin particles, free or interacting, cannot couple to gravity while preserving causality unless there exist higher spin states in the gravitational sector much below the Planck scale. Causality imposes an upper bound on the mass of the lightest higher spin particle in the gravity sector in terms of quantities in the non-gravitational sector. I will argue that any weakly coupled UV completion of such a theory must have a gravity sector containing infinite towers of asymptotically parallel, equispaced, and linear Regge trajectories. This implies that the gravity sector has a stringy structure with an upper bound on the string scale. Another consequence of this bound is that all metastable higher spin particles in 4d with masses below the string scale must satisfy a weak gravity condition. Moreover, these bounds also have surprising implications for large N QCD coupled to gravity and cosmology.
[please email a.held@imperial.ac.uk for zoom link or password]
I will show that metastable higher spin particles, free or interacting, cannot couple to gravity while preserving causality unless there exist higher spin states in the gravitational sector much below the Planck scale. Causality imposes an upper bound on the mass of the lightest higher spin particle in the gravity sector in terms of quantities in the non-gravitational sector. I will argue that any weakly coupled UV completion of such a theory must have a gravity sector containing infinite towers of asymptotically parallel, equispaced, and linear Regge trajectories. This implies that the gravity sector has a stringy structure with an upper bound on the string scale. Another consequence of this bound is that all metastable higher spin particles in 4d with masses below the string scale must satisfy a weak gravity condition. Moreover, these bounds also have surprising implications for large N QCD coupled to gravity and cosmology.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
9 Nov 2020
Branes and the moduli space of instantons
Amihay Hanany
(Imperial College)
Abstract:
The first recorded lecture of the London Theory Institute for PhD Students. Link to recording and problems (to be solved in live Zoom session next Monday) as well as registration details at
https://lonti.weebly.com/
and
https://youtu.be/CGDNipeuVEs
Instantons, or solutions to the self dual Yang Mills (SDYM) equations are well known solutions, introduced in the mid 70s and played a role in a host of applications in QFT and String Theory. This talk will show a simple brane construction which allows the computation of the moduli space of solutions to the SDYM equations, introduce the student to the world of quivers, and demonstrate simple computations which allow evaluations of these moduli spaces.
The first recorded lecture of the London Theory Institute for PhD Students. Link to recording and problems (to be solved in live Zoom session next Monday) as well as registration details at
https://lonti.weebly.com/
and
https://youtu.be/CGDNipeuVEs
Instantons, or solutions to the self dual Yang Mills (SDYM) equations are well known solutions, introduced in the mid 70s and played a role in a host of applications in QFT and String Theory. This talk will show a simple brane construction which allows the computation of the moduli space of solutions to the SDYM equations, introduce the student to the world of quivers, and demonstrate simple computations which allow evaluations of these moduli spaces.
Posted by: CityU2
Thu
5 Nov 2020
Stringy resurgence: modular graph functions and Poincare series
Daniele Dorigoni
(Durham University)
Abstract:
Zoom link: Please email Silvia Nagy (s.nagyATqmul.ac.uk) or Jungwook Kim (jung-wook.kimATqmul.ac.uk) for the zoom link.
Abstract:In string theory SL(2,Z) invariant functions, such as modular graph functions or coefficient functions of higher derivative corrections, are ubiquitous. Using a representation in terms of Poincarรยฉ series we can combine different methods for asymptotic expansions and obtain the complete perturbative and non-perturbative expansion. In the case of the higher derivative corrections, these terms have an interpretation in terms of perturbative string loop effects and pairs of instantons/anti-instantons.
There will also be a pre-seminar for the students which will begin at 2:30 pm.
Zoom link: Please email Silvia Nagy (s.nagyATqmul.ac.uk) or Jungwook Kim (jung-wook.kimATqmul.ac.uk) for the zoom link.
Abstract:In string theory SL(2,Z) invariant functions, such as modular graph functions or coefficient functions of higher derivative corrections, are ubiquitous. Using a representation in terms of Poincarรยฉ series we can combine different methods for asymptotic expansions and obtain the complete perturbative and non-perturbative expansion. In the case of the higher derivative corrections, these terms have an interpretation in terms of perturbative string loop effects and pairs of instantons/anti-instantons.
There will also be a pre-seminar for the students which will begin at 2:30 pm.
Posted by: QMW
Thu
5 Nov 2020
Non-planar N=4 SYM: from integrability to quantum chaos
Tristan McLoughlin
(Trinity College Dublin)
Abstract:
In this talk we will consider the spectrum of anomalous dimensions in N=4 super-Yang-Mills and related theories. We will first discuss the emergence of quantum chaos as one goes from infinite to finite N and how the perturbative spectrum is described by GOE random matrix theory. We will then describe how the integrability of the planar-limit can be used to rewrite the computation of the leading 1/N corrections to the one-loop anomalous dimensions in terms of scalar products of off-shell Bethe states or, alternatively, hexagon-like functions.–– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
In this talk we will consider the spectrum of anomalous dimensions in N=4 super-Yang-Mills and related theories. We will first discuss the emergence of quantum chaos as one goes from infinite to finite N and how the perturbative spectrum is described by GOE random matrix theory. We will then describe how the integrability of the planar-limit can be used to rewrite the computation of the leading 1/N corrections to the one-loop anomalous dimensions in terms of scalar products of off-shell Bethe states or, alternatively, hexagon-like functions.–– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
4 Nov 2020
Type-B Anomalies on the Higgs Branch
๐ London
Elli Pomoni
(DESY)
Abstract:
In this talk we will study type-B conformal anomalies associated with
1/2-BPS Coulomb-branch operators in 4D N=2 SCFTs. We will derive the
conditions under which these anomalies can match across the conformal
phase and the Higgs phase, and explicitly see them at work in concrete
examples of both matching and non-matching. On the one hand matching
leads to a new class of data on the Higgs branch of 4D N=2 SCFTs that
are exactly computable. On the other, non-matching imposes novel
restrictions on the holonomy of the conformal manifold.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]
In this talk we will study type-B conformal anomalies associated with
1/2-BPS Coulomb-branch operators in 4D N=2 SCFTs. We will derive the
conditions under which these anomalies can match across the conformal
phase and the Higgs phase, and explicitly see them at work in concrete
examples of both matching and non-matching. On the one hand matching
leads to a new class of data on the Higgs branch of 4D N=2 SCFTs that
are exactly computable. On the other, non-matching imposes novel
restrictions on the holonomy of the conformal manifold.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]
Posted by: andrea
Tue
3 Nov 2020
Dark Energy and String Theory
Susha Parameswaran
(University of Liverpool)
Abstract:
I will give a (biased) review on the main current ideas to explain the fundamental nature of Dark Energy using string theory. The possibility of a de Sitter vacuum in string theory, corresponding to a cosmological constant with w=-1, has proven difficult to achieve, leading to the conjecture that such vacua might lie in the String Theory Swampland. Other interesting string candidates include axion or runaway quintessence. I will in particular discuss the Thermal Dark Energy proposal. Here finite temperature effects in a light hidden sector hold a hidden scalar away from the minimum of its zero-temperature potential, leading to an effective cosmological constant, consistently with the Swampland Conjectures and with potentially observable consequences.
[please email a.held@imperial.ac.uk for zoom link or password]
I will give a (biased) review on the main current ideas to explain the fundamental nature of Dark Energy using string theory. The possibility of a de Sitter vacuum in string theory, corresponding to a cosmological constant with w=-1, has proven difficult to achieve, leading to the conjecture that such vacua might lie in the String Theory Swampland. Other interesting string candidates include axion or runaway quintessence. I will in particular discuss the Thermal Dark Energy proposal. Here finite temperature effects in a light hidden sector hold a hidden scalar away from the minimum of its zero-temperature potential, leading to an effective cosmological constant, consistently with the Swampland Conjectures and with potentially observable consequences.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
2 Nov 2020
Global symmetry, Euclidean gravity, and the black hole information problem
Daniel Harlow
(MIT)
Abstract:
Part of the London Black Hole Information Paradox Journal Club (for Zoom link, please subscribe here: https://forms.gle/wLYi4A72tEUwuzGK6)
Part of the London Black Hole Information Paradox Journal Club (for Zoom link, please subscribe here: https://forms.gle/wLYi4A72tEUwuzGK6)
Posted by: andrea
October 2020
Thu
29 Oct 2020
From Quantum Field Theory to Quantum Gravity and the Sachdev-Ye-Kitaev model
Adrian Tanasa
(Univ. Bordeaux)
Abstract:
Zoom link: Please email Silvia Nagy (s.nagyATqmul.ac.uk) or Jungwook Kim (jung-wook.kimATqmul.ac.uk) for the zoom link
Abstract: In the first part of this talk I will briefly introduce 0-dimensional Quantum Field Theory (QFT) and Matrix Models, which are known to be a succesfull discrete geometrical, QFT approach to 2D Quantum Gravity. I will then move on to Tensor Models, seen as natural QFT generalization of the celebrated Matrix Models. In the next part of the talk I will present the Sachdev-Ye-Kitaev model, which is known to be a toy model for holography, as well as the relations of this SYK model with various Tensor Models. Finally, I will present some recent results on these topics (various diagrammatic results but also the study of the effect of non-Gaussian average over the SYK random couplings).
Zoom link: Please email Silvia Nagy (s.nagyATqmul.ac.uk) or Jungwook Kim (jung-wook.kimATqmul.ac.uk) for the zoom link
Abstract: In the first part of this talk I will briefly introduce 0-dimensional Quantum Field Theory (QFT) and Matrix Models, which are known to be a succesfull discrete geometrical, QFT approach to 2D Quantum Gravity. I will then move on to Tensor Models, seen as natural QFT generalization of the celebrated Matrix Models. In the next part of the talk I will present the Sachdev-Ye-Kitaev model, which is known to be a toy model for holography, as well as the relations of this SYK model with various Tensor Models. Finally, I will present some recent results on these topics (various diagrammatic results but also the study of the effect of non-Gaussian average over the SYK random couplings).
Posted by: QMW
Thu
29 Oct 2020
The TTbar deformation and a promising 4D generalisation
Roberto Tateo
(University of Torino)
Abstract:
Two-dimensional field theories deformed by Zamolodchikov's TTbar operator have recently attracted the attention of theoretical physicists due to the many important links with string theory and AdS/CFT.
In this talk, I will describe various classical and quantum aspects of this particular irrelevant perturbation, including its geometrical interpretation at the classical level.
I will also introduce a generalisation of this geometrical framework to 4D field theories, and discuss some of the interesting differences with the 2D case. –– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
Two-dimensional field theories deformed by Zamolodchikov's TTbar operator have recently attracted the attention of theoretical physicists due to the many important links with string theory and AdS/CFT.
In this talk, I will describe various classical and quantum aspects of this particular irrelevant perturbation, including its geometrical interpretation at the classical level.
I will also introduce a generalisation of this geometrical framework to 4D field theories, and discuss some of the interesting differences with the 2D case. –– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
28 Oct 2020
Non-perturbative physics for JT gravity and supergravity
Clifford Johnson
(USC)
Abstract:
JackiwรขโฌโTeitelboim (JT) gravity and supergravity theories are exciting solvable models that teach us about low temperature black hole dynamics, and aspects of quantum chaotic behaviour. They have been shown (by Saad, Shenker and Stanford, and by Stanford and Witten) to have double scaled random matrix model descriptions, capturing the (spacetime) topological perturbative expansion of the partition function. I will describe an alternative method for building the matrix model description, using techniques from minimal string theory. This method is particularly useful for supplying non-perturbative definitions of the physics. I show how this allows for the computation of key aspects of the physics at low energy and temperature.
For the zoom link, please email antoine.brgt@gmail.com
JackiwรขโฌโTeitelboim (JT) gravity and supergravity theories are exciting solvable models that teach us about low temperature black hole dynamics, and aspects of quantum chaotic behaviour. They have been shown (by Saad, Shenker and Stanford, and by Stanford and Witten) to have double scaled random matrix model descriptions, capturing the (spacetime) topological perturbative expansion of the partition function. I will describe an alternative method for building the matrix model description, using techniques from minimal string theory. This method is particularly useful for supplying non-perturbative definitions of the physics. I show how this allows for the computation of key aspects of the physics at low energy and temperature.
For the zoom link, please email antoine.brgt@gmail.com
Posted by: IC
Tue
27 Oct 2020
Moduli stars
Francesco Muia
(Theory Group DESY)
Abstract:
The recent direct detection of gravitational waves (GWs) has opened a new window of observation for physical phenomena in which gravity is the dominant interaction. Collisions of black holes and neutron stars have been observed and a plethora of new events, even involving new physics, are expected to be detected in the next few years. It is natural to explore alternative physical objects that may exist which are different from the standard stars and black holes and that could lead to particular imprints on the GW spectrum. In this talk I will explore the possibility that moduli (gravitationally coupled scalar fields arising in all string compactifications) can compose star-like objects (moduli stars) whose dynamics gives rise to GW production. I will illustrate their formation in the early universe, that has been studied through lattice techniques. After their formation moduli stars can have different behaviours, e.g. they could rapidly collapse to black holes or disperse into scalar radiation, resulting in different phenomenology. I will describe the fate of moduli stars, that has been investigated through numerical relativity techniques.
[please email a.held@imperial.ac.uk for zoom link or password]
The recent direct detection of gravitational waves (GWs) has opened a new window of observation for physical phenomena in which gravity is the dominant interaction. Collisions of black holes and neutron stars have been observed and a plethora of new events, even involving new physics, are expected to be detected in the next few years. It is natural to explore alternative physical objects that may exist which are different from the standard stars and black holes and that could lead to particular imprints on the GW spectrum. In this talk I will explore the possibility that moduli (gravitationally coupled scalar fields arising in all string compactifications) can compose star-like objects (moduli stars) whose dynamics gives rise to GW production. I will illustrate their formation in the early universe, that has been studied through lattice techniques. After their formation moduli stars can have different behaviours, e.g. they could rapidly collapse to black holes or disperse into scalar radiation, resulting in different phenomenology. I will describe the fate of moduli stars, that has been investigated through numerical relativity techniques.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Fri
23 Oct 2020
Renormalons from Resurgence
๐ London
Tomas Reis
(University of Geneva)
Abstract:
In this talk I will present the use of resurgence techniques in identifying non-perturbation physics and its relation to renormalons, in light of recent work of Marcos Mariรยฑo and me. This exploration has touched 1+1 QFTs and condensed matter systems, revealing that the presence of renormalons is more widespread than expected. After introducing both ideas in the title, I will specialise in the case of the 1D fermion gas with dirac-delta attractive potential. This case is a clean example of our approach and unveils a curious interplay between resurgence, renormalons, and superconductivity. [Please email damian.galante@klc.ac.uk for the link]
In this talk I will present the use of resurgence techniques in identifying non-perturbation physics and its relation to renormalons, in light of recent work of Marcos Mariรยฑo and me. This exploration has touched 1+1 QFTs and condensed matter systems, revealing that the presence of renormalons is more widespread than expected. After introducing both ideas in the title, I will specialise in the case of the 1D fermion gas with dirac-delta attractive potential. This case is a clean example of our approach and unveils a curious interplay between resurgence, renormalons, and superconductivity. [Please email damian.galante@klc.ac.uk for the link]
Posted by: andrea
Thu
22 Oct 2020
An exact AdS/CFT correspondence
Lorenz Eberhardt
(IAS)
Abstract:
One incarnation of the AdS/CFT correspondence is the duality between the symmetric product orbifold of T4 and superstrings on AdS3xS3xT4 with one unit of NS-NS flux. Compared to other instances of AdS/CFT, this duality is much simpler and can in principle be fully understood. I will give a broad overview of the inner workings of the duality from a worldsheet CFT point of view, physical lessons and connections to integrability. –– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
One incarnation of the AdS/CFT correspondence is the duality between the symmetric product orbifold of T4 and superstrings on AdS3xS3xT4 with one unit of NS-NS flux. Compared to other instances of AdS/CFT, this duality is much simpler and can in principle be fully understood. I will give a broad overview of the inner workings of the duality from a worldsheet CFT point of view, physical lessons and connections to integrability. –– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
21 Oct 2020
Liouville and JT quantum gravity - holography and matrix models
๐ London
Thomas Mertens
(GENT U.)
Abstract:
In this talk, we will discuss recent progress in understanding quantum gravity amplitudes (partition function and boundary correlation functions) in Liouville gravity, and how they limit to Jackiw-Teitelboim (JT) correlators. We also discuss multiboundary and higher genus amplitudes. We focus on two main results: the Liouville gravity answers look like q-deformations of the JT answers, and Liouville gravity can be related to a 2d dilaton gravity with a sinh dilaton potential. We end with discussions on supersymmetric extensions and work in progress. Based largely on arXiv:2006.07072 and 2007.00998รขโฌโน.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]
In this talk, we will discuss recent progress in understanding quantum gravity amplitudes (partition function and boundary correlation functions) in Liouville gravity, and how they limit to Jackiw-Teitelboim (JT) correlators. We also discuss multiboundary and higher genus amplitudes. We focus on two main results: the Liouville gravity answers look like q-deformations of the JT answers, and Liouville gravity can be related to a 2d dilaton gravity with a sinh dilaton potential. We end with discussions on supersymmetric extensions and work in progress. Based largely on arXiv:2006.07072 and 2007.00998รขโฌโน.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]
Posted by: andrea
Tue
20 Oct 2020
Pushing the limits of the double copy
Mariana Carrillo
(Imperial College London)
Abstract:
The double copy in its original form allows us to obtain scattering amplitudes of gravity as the "square" of those of Yang Mills. I will explain how this squaring procedure works and how this relationship has been extended to classical solutions. I will also briefly mentioned how the double copy relationship can be extended to scalar effective field theories.
[please email a.held@imperial.ac.uk for zoom link or password]
The double copy in its original form allows us to obtain scattering amplitudes of gravity as the "square" of those of Yang Mills. I will explain how this squaring procedure works and how this relationship has been extended to classical solutions. I will also briefly mentioned how the double copy relationship can be extended to scalar effective field theories.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Tue
20 Oct 2020
Integrable deformations and the doubled formalism
Yuta Sekiguchi
(Imperial College London)
Abstract:
The integrable deformation of string backgrounds has been one of the significant research directions to construct a variety of examples of gauge/gravity duality preserving integrability and to push forward the confirmation of AdS/CFT correspondence. In this introductory talk, I plan to give a basic review of classical integrability of string sigma models with a focus on Lax pairs, to consider the role of the doubled sigma model.
[please email a.held@imperial.ac.uk for zoom link or password]
The integrable deformation of string backgrounds has been one of the significant research directions to construct a variety of examples of gauge/gravity duality preserving integrability and to push forward the confirmation of AdS/CFT correspondence. In this introductory talk, I plan to give a basic review of classical integrability of string sigma models with a focus on Lax pairs, to consider the role of the doubled sigma model.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
15 Oct 2020
Covariant phase space with boundaries (please email p.agarwal AT qmul.ac.uk for the zoom link)
Daniel Harlow
(MIT)
Abstract:
The Hamiltonian formulation of mechanics has many advantages,
but its standard presentation destroys manifest covariance. This can be
avoided by using the "covariant phase formalism" of Iyer and Wald, but
until recently this formalism has suffered from several ambiguities
related to boundary terms and total derivatives. In this talk I will
present a new version of the formalism which incorporates boundary
effects from the beginning. This eliminates all ambiguities, and leads
to an algorithmic procedure for covariantly constructing the phase space
and Hamiltonian of any Lagrangian field theory. It also allows us to
confirm that the Poisson bracket in covariant phase space is indeed
equivalent to an old proposal of Peierls for computing Poisson brackets
covariantly. Along the way I'll illustrate the formalism using various
examples. Based on work with Jie-qiang Wu.
The Hamiltonian formulation of mechanics has many advantages,
but its standard presentation destroys manifest covariance. This can be
avoided by using the "covariant phase formalism" of Iyer and Wald, but
until recently this formalism has suffered from several ambiguities
related to boundary terms and total derivatives. In this talk I will
present a new version of the formalism which incorporates boundary
effects from the beginning. This eliminates all ambiguities, and leads
to an algorithmic procedure for covariantly constructing the phase space
and Hamiltonian of any Lagrangian field theory. It also allows us to
confirm that the Poisson bracket in covariant phase space is indeed
equivalent to an old proposal of Peierls for computing Poisson brackets
covariantly. Along the way I'll illustrate the formalism using various
examples. Based on work with Jie-qiang Wu.
Posted by: QMW
Thu
15 Oct 2020
QQ-system construction for so(2r) spin chains
Rouven Frassek
(ENS Paris)
Abstract:
I will review the QQ-system and oscillator construction of Q-operators for su(r+1) spin chains and discuss its generalisation to so(2r) spin chains. ––- Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
I will review the QQ-system and oscillator construction of Q-operators for su(r+1) spin chains and discuss its generalisation to so(2r) spin chains. ––- Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
14 Oct 2020
Polygon Seminar (Zoom)–Quantum codes, lattices, and CFTs. (Please contact your local Triangle/Polygon organiser for the Zoom info)
Anatoly Dymarsky
(U. Kentucky)
Abstract:
There is a deep relation between classical error-correcting codes, Euclidean lattices, and chiral 2d CFTs. We show this relation extends to include quantum codes, Lorentzian lattices, and non-chiral CFTs. The relation to quantum codes provides a simple way to solve modular bootstrap constraints and identify interesting examples of conformal theories. In particular we construct many examples of physically distinct isospectral theories, examples of "would-be" CFT partition function – non-holomorphic functions satisfying all constraints of the modular bootstrap, yet not associated with any known CFT, and find theory with the maximal spectral gap among all Narain CFTs with the central charge c=4. At the level of code theories the problem of finding maximal spectral gap reduces to the problem of finding optimal code, leading to "baby bootstrap" program. We also discuss averaging over the ensemble of all CFTs associated with quantum codes, and its possible holographic interpretation. The talk is based on arXiv:2009.01236 and arXiv:2009.01244.
There is a deep relation between classical error-correcting codes, Euclidean lattices, and chiral 2d CFTs. We show this relation extends to include quantum codes, Lorentzian lattices, and non-chiral CFTs. The relation to quantum codes provides a simple way to solve modular bootstrap constraints and identify interesting examples of conformal theories. In particular we construct many examples of physically distinct isospectral theories, examples of "would-be" CFT partition function – non-holomorphic functions satisfying all constraints of the modular bootstrap, yet not associated with any known CFT, and find theory with the maximal spectral gap among all Narain CFTs with the central charge c=4. At the level of code theories the problem of finding maximal spectral gap reduces to the problem of finding optimal code, leading to "baby bootstrap" program. We also discuss averaging over the ensemble of all CFTs associated with quantum codes, and its possible holographic interpretation. The talk is based on arXiv:2009.01236 and arXiv:2009.01244.
Posted by: QMW
Tue
13 Oct 2020
Deforming integrable symmetries
Fiona Seibold
(Imperial College London)
Abstract:
Integrable models are the cornerstones of theoretical physics, simple enough to be solved exactly and yet rich enough to offer a glimpse into the dynamics of more intricate systems. Also two-dimensional field theories or string theories can be integrable. In this talk I will discuss integrability in field and string theories and present a special class of integrable models that promote the symmetry algebra of the undeformed theory to a quantum group.
[please email a.held@imperial.ac.uk for zoom link or password]
Integrable models are the cornerstones of theoretical physics, simple enough to be solved exactly and yet rich enough to offer a glimpse into the dynamics of more intricate systems. Also two-dimensional field theories or string theories can be integrable. In this talk I will discuss integrability in field and string theories and present a special class of integrable models that promote the symmetry algebra of the undeformed theory to a quantum group.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Tue
13 Oct 2020
Supersymmetry and Computation
Marcos Crichigno
(Imperial College London)
Abstract:
I will discuss some aspects of supersymmetric systems from a computational perspective.
[please email a.held@imperial.ac.uk for zoom link or password]
I will discuss some aspects of supersymmetric systems from a computational perspective.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
8 Oct 2020
Integrability for Feynman Integrals
Florian Loebbert
(Humboldt University of Berlin)
Abstract:
In this talk I give an overview of the Yangian symmetry of Feynman integrals. After reviewing the connection between AdS/CFT integrability and the Yangian symmetry of massless Feynman graphs, I discuss the idea to bootstrap Feynman integrals based on the Yangian constraints. Then I show that also in the massive case large classes of Feynman integrals are constrained by a Yangian extension of dual conformal symmetry. When translated to momentum space, this leads to a novel massive generalization of ordinary conformal symmetry. Finally, I argue that these features of massive Feynman integrals can be understood as the integrability of planar scattering amplitudes in a massive version of the so-called fishnet theory, which is obtained as a double-scaling limit of N=4 super Yang-Mills theory on the Coulomb branch.
–– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
In this talk I give an overview of the Yangian symmetry of Feynman integrals. After reviewing the connection between AdS/CFT integrability and the Yangian symmetry of massless Feynman graphs, I discuss the idea to bootstrap Feynman integrals based on the Yangian constraints. Then I show that also in the massive case large classes of Feynman integrals are constrained by a Yangian extension of dual conformal symmetry. When translated to momentum space, this leads to a novel massive generalization of ordinary conformal symmetry. Finally, I argue that these features of massive Feynman integrals can be understood as the integrability of planar scattering amplitudes in a massive version of the so-called fishnet theory, which is obtained as a double-scaling limit of N=4 super Yang-Mills theory on the Coulomb branch.
–– Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
7 Oct 2020
The butterfly effect away from maximal chaos
๐ London
Gabor Sarosi
(CERN)
Abstract:
A simple probe of chaos and operator growth in many-body quantum systems is the thermal out of time ordered (OTO) four point function. In a large class of local systems, the effects of chaos in this correlator build up exponentially fast inside a so called butterfly cone. I will discuss universal features of the spatiotemporal structure of this exponential growth in large N systems. In particular I will argue that there can be a smaller, รขโฌลscramblonรขโฌย cone inside the butterfly cone. Outside the scramblon cone, the growth of the OTO four point function is completely universal and saturates a chaos bound. I will explain the connection to conformal Regge theory, where crossing the scramblon cone is related to an exchange of dominance between the pomeron and the stress tensor. Finally, I will discuss a connection between chaos and energy transport, called the pole skipping phenomenon, which is a subtle effect in the thermal energy density retarded two point function at a special point in the complex frequency and momentum planes. I will present an improved understanding of this connection and test it in the large q limit of an SYK chain, where I determine both the Lyapunov growth of the OTO correlator and the energy density two point function exactly as a function of the coupling, interpolating between weekly coupled and maximally chaotic behaviour.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]
A simple probe of chaos and operator growth in many-body quantum systems is the thermal out of time ordered (OTO) four point function. In a large class of local systems, the effects of chaos in this correlator build up exponentially fast inside a so called butterfly cone. I will discuss universal features of the spatiotemporal structure of this exponential growth in large N systems. In particular I will argue that there can be a smaller, รขโฌลscramblonรขโฌย cone inside the butterfly cone. Outside the scramblon cone, the growth of the OTO four point function is completely universal and saturates a chaos bound. I will explain the connection to conformal Regge theory, where crossing the scramblon cone is related to an exchange of dominance between the pomeron and the stress tensor. Finally, I will discuss a connection between chaos and energy transport, called the pole skipping phenomenon, which is a subtle effect in the thermal energy density retarded two point function at a special point in the complex frequency and momentum planes. I will present an improved understanding of this connection and test it in the large q limit of an SYK chain, where I determine both the Lyapunov growth of the OTO correlator and the energy density two point function exactly as a function of the coupling, interpolating between weekly coupled and maximally chaotic behaviour.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]
Posted by: andrea
Tue
6 Oct 2020
Courant algebroids, Poisson-Lie T-duality and supergravity (of type II)
Fridrich Valach
(Imperial College London)
Abstract:
Description:
Courant algebroids provide a natural framework for working with the low energy limits of string theory. In particular, they are well suited for the study of Poisson-Lie T-duality, which is a generalization of the usual T-duality. We will discuss how to see bosonic fields of type II supergravity as structures on Courant algebroids (generalized metrics, spinors and divergence operators). We will then construct appropriate curvature tensors and use them to prove the compatibility of Poisson-Lie T-duality and the equations of motion of supergravity. The framework also allows us to use algebraic methods to search for new (non-isometric) string backgrounds. This is a joint work with Pavol ร ย evera.
[please email a.held@imperial.ac.uk for zoom-link]
Description:
Courant algebroids provide a natural framework for working with the low energy limits of string theory. In particular, they are well suited for the study of Poisson-Lie T-duality, which is a generalization of the usual T-duality. We will discuss how to see bosonic fields of type II supergravity as structures on Courant algebroids (generalized metrics, spinors and divergence operators). We will then construct appropriate curvature tensors and use them to prove the compatibility of Poisson-Lie T-duality and the equations of motion of supergravity. The framework also allows us to use algebraic methods to search for new (non-isometric) string backgrounds. This is a joint work with Pavol ร ย evera.
[please email a.held@imperial.ac.uk for zoom-link]
Posted by: IC
Tue
6 Oct 2020
Extended symmetries in field theory and gravity
Karapet Mkrtchyan
(Imperial College London)
Abstract:
I will summarise my research interests and recent work, which is mainly related to the problems of field and gravity theories with extended symmetries. Such systems are the higher-spin and coloured gravity theories, theories of non-abelian chiral p-forms or partially-massless fields (satisfactory interacting theories of which are still missing).
[please email a.held@imperial.ac.uk for zoom-link]
I will summarise my research interests and recent work, which is mainly related to the problems of field and gravity theories with extended symmetries. Such systems are the higher-spin and coloured gravity theories, theories of non-abelian chiral p-forms or partially-massless fields (satisfactory interacting theories of which are still missing).
[please email a.held@imperial.ac.uk for zoom-link]
Posted by: IC
Thu
1 Oct 2020
BPS counting with exponential networks (email p.agarwal AT qmul.ac.uk for the zoom link))
Pietro Longhi
(ETH Zurich)
Abstract:
Spectral networks compute certain enumerative invariants associated with Hitchin systems, by focusing on the interplay of certain geometric and combinatorial data within them. In physics, spectral networks count BPS states of class S theories through 2d-4d wall crossing. I will describe a 3d-5d uplift of this based on exponential networks, that computes generalized Donaldson-Thomas invariants of toric Calabi Yau threefolds.
Spectral networks compute certain enumerative invariants associated with Hitchin systems, by focusing on the interplay of certain geometric and combinatorial data within them. In physics, spectral networks count BPS states of class S theories through 2d-4d wall crossing. I will describe a 3d-5d uplift of this based on exponential networks, that computes generalized Donaldson-Thomas invariants of toric Calabi Yau threefolds.
Posted by: QMW
Thu
1 Oct 2020
Multi-point Bootstrap and Integrability
Pedro Vieira
(ICTP SAIFR )
Abstract:
t.b.a. –––- Part of London Integrability Journal Club. If you are a new particiant, please register using the form on our website integrability-london.weebly.com. The link will be emailed.
t.b.a. –––- Part of London Integrability Journal Club. If you are a new particiant, please register using the form on our website integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
September 2020
Wed
30 Sep 2020
Lorentzian CFT 3-point functions and the ANEC
๐ London
Teresa Bautista Solans
(KCL)
Abstract:
In CFT, the expressions for Euclidean 3-point functions in momentum space were fully obtained in recent years, but their Lorentzian counterparts have remained quite unknown. In this talk I will present the expression for the Lorentzian 3-point function of scalars, and further show a way to obtain tensorial ones. As I will argue, such momentum-space expressions simplify considerably the computation of the expectation values of the ANEC (Average Null Energy Condition) operator on the states used in the conformal colliders setting, whose positivity has been used to put interesting bounds on conformal anomalies. With the motivation of generalising these bounds and studying the implications of the ANEC for QFT, I will discuss perturbative corrections to the simplest ANEC expectation values in lambda-phi4 theory.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]
In CFT, the expressions for Euclidean 3-point functions in momentum space were fully obtained in recent years, but their Lorentzian counterparts have remained quite unknown. In this talk I will present the expression for the Lorentzian 3-point function of scalars, and further show a way to obtain tensorial ones. As I will argue, such momentum-space expressions simplify considerably the computation of the expectation values of the ANEC (Average Null Energy Condition) operator on the states used in the conformal colliders setting, whose positivity has been used to put interesting bounds on conformal anomalies. With the motivation of generalising these bounds and studying the implications of the ANEC for QFT, I will discuss perturbative corrections to the simplest ANEC expectation values in lambda-phi4 theory.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]
Posted by: andrea
Thu
24 Sep 2020
Neural Networks and Quantum Field Theory (please email p.agarwal AT qmul.ac.uk for the zoom link)
Jim Halverson
(Northeastern University in Boston)
Abstract:
We propose a theoretical understanding of neural networks in terms of Wilsonian effective field theory. The correspondence relies on the fact that many asymptotic neural networks are drawn from Gaussian processes, the analog of non-interacting field theories. Moving away from the asymptotic limit yields a non-Gaussian process and corresponds to turning on particle interactions, allowing for the computation of correlation functions of neural network outputs with Feynman diagrams. Minimal non-Gaussian process likelihoods are determined by the most relevant non-Gaussian terms, according to the flow in their coefficients induced by the Wilsonian renormalization group. This yields a direct connection between overparameterization and simplicity of neural network likelihoods. Whether the coefficients are constants or functions may be understood in terms of GP limit symmetries, as expected from 't Hooft's technical naturalness. General theoretical calculations are matched to neural network experiments in the simplest class of models allowing the correspondence. Our formalism is valid for any of the many architectures that becomes a GP in an asymptotic limit, a property preserved under certain types of training.
We propose a theoretical understanding of neural networks in terms of Wilsonian effective field theory. The correspondence relies on the fact that many asymptotic neural networks are drawn from Gaussian processes, the analog of non-interacting field theories. Moving away from the asymptotic limit yields a non-Gaussian process and corresponds to turning on particle interactions, allowing for the computation of correlation functions of neural network outputs with Feynman diagrams. Minimal non-Gaussian process likelihoods are determined by the most relevant non-Gaussian terms, according to the flow in their coefficients induced by the Wilsonian renormalization group. This yields a direct connection between overparameterization and simplicity of neural network likelihoods. Whether the coefficients are constants or functions may be understood in terms of GP limit symmetries, as expected from 't Hooft's technical naturalness. General theoretical calculations are matched to neural network experiments in the simplest class of models allowing the correspondence. Our formalism is valid for any of the many architectures that becomes a GP in an asymptotic limit, a property preserved under certain types of training.
Posted by: QMW
Thu
24 Sep 2020
Geometrical four-point functions in the 2d critical Q-state Potts model
Yifei He
(IPhT Saclay)
Abstract:
An important example among the 2d geometrical critical phenomena is the critical Q-state Potts model, which describes the percolation in the limit Q–>1. In this talk I will consider the problem of determining the geometrical four-point functions (cluster connectivities) in this model. Connections with the minimal models are made which uncover remarkable properties of the Potts amplitudes. Such properties allow to deduce the existence of "interchiral conformal blocks" which can be constructed using the degeneracy in the Potts spectrum. Using these, I will then determine the four-point functions through numerical bootstrap. In addition, I will also discuss the logarithmic nature of the Potts CFT and hints of a full analytic solution of the model.
––- Part of London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com. The link will be emailed.
An important example among the 2d geometrical critical phenomena is the critical Q-state Potts model, which describes the percolation in the limit Q–>1. In this talk I will consider the problem of determining the geometrical four-point functions (cluster connectivities) in this model. Connections with the minimal models are made which uncover remarkable properties of the Potts amplitudes. Such properties allow to deduce the existence of "interchiral conformal blocks" which can be constructed using the degeneracy in the Potts spectrum. Using these, I will then determine the four-point functions through numerical bootstrap. In addition, I will also discuss the logarithmic nature of the Potts CFT and hints of a full analytic solution of the model.
––- Part of London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Thu
17 Sep 2020
't Hooft operators and Q-functions
Davide Gaiotto
(Perimeter Institute)
Abstract:
I will describe the role of 't Hooft operators in 4d Chern-Simons theory and applications to integrability.
––––––––––- Part of London Integrability Journal Club. If you are a new participant, please register using the form at integrability-london.weebly.com. The link will be emailed.
I will describe the role of 't Hooft operators in 4d Chern-Simons theory and applications to integrability.
––––––––––- Part of London Integrability Journal Club. If you are a new participant, please register using the form at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Tue
8 Sep 2020
Entanglement entropies of equilibrated pure states in quantum many-body systems and replica wormholes
Hong Liu
(MIT)
Abstract:
We develop a universal approximation for the Renyi entropies of a pure state at late times in non-integrable systems, which macroscopically resembles an equilibrium density matrix. The resulting expressions are fully determined by properties of the associated equilibrium density matrix, and are hence independent of the details of the initial state, while also being manifestly consistent with unitary time-evolution. For equilibrated pure states in gravity systems, such as those involving black holes, this approximation gives a prescription for calculating entanglement entropies using Euclidean path integrals which is consistent with unitarity and hence can be used to address the information loss paradox of Hawking. Applied to recent models of evaporating black holes and eternal black holes coupled to baths, it provides a derivation of replica wormholes, and elucidates their mathematical and physical origins. In particular, it shows that replica wormholes can arise in a system with a fixed Hamiltonian, without the need for ensemble averages. ––- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi).
We develop a universal approximation for the Renyi entropies of a pure state at late times in non-integrable systems, which macroscopically resembles an equilibrium density matrix. The resulting expressions are fully determined by properties of the associated equilibrium density matrix, and are hence independent of the details of the initial state, while also being manifestly consistent with unitary time-evolution. For equilibrated pure states in gravity systems, such as those involving black holes, this approximation gives a prescription for calculating entanglement entropies using Euclidean path integrals which is consistent with unitarity and hence can be used to address the information loss paradox of Hawking. Applied to recent models of evaporating black holes and eternal black holes coupled to baths, it provides a derivation of replica wormholes, and elucidates their mathematical and physical origins. In particular, it shows that replica wormholes can arise in a system with a fixed Hamiltonian, without the need for ensemble averages. ––- Follow the usual link or contact the organisers (Antoine Bourget and Edoardo Vescovi).
Posted by: IC