Triangle Seminars
December 2021
Wed
15 Dec 2021
Near AdS_2 spectroscopy
๐ London
Alejandra Castro
(UvA)
Abstract:
In this talk I will describe holographic properties of near-AdS_2 spacetimes that arise within spherically symmetric configurations of N=2 4D supergravity, for both gauged and ungauged theories. These theories pose a rich space of AdS_2xS^2 backgrounds, and their responses in the near-AdS_2 region are not universal. I will show that the spectrum of operators dual to the matter fields, and their cubic interactions, are sensitive to properties of the background and the theory it is embedded in. The properties that have the most striking effect are whether the background is BPS or non-BPS, and if the theory is gauged or ungauged. The resulting differences will have an imprint on the quantum nature of the microstates of near-extremal black holes, reflecting that not all extremal black holes respond equally when kicked away from extremality.
In this talk I will describe holographic properties of near-AdS_2 spacetimes that arise within spherically symmetric configurations of N=2 4D supergravity, for both gauged and ungauged theories. These theories pose a rich space of AdS_2xS^2 backgrounds, and their responses in the near-AdS_2 region are not universal. I will show that the spectrum of operators dual to the matter fields, and their cubic interactions, are sensitive to properties of the background and the theory it is embedded in. The properties that have the most striking effect are whether the background is BPS or non-BPS, and if the theory is gauged or ungauged. The resulting differences will have an imprint on the quantum nature of the microstates of near-extremal black holes, reflecting that not all extremal black holes respond equally when kicked away from extremality.
Posted by: andrea
Mon
13 Dec 2021
The Science of Storytelling
Alison Woollard
(Oxford University)
Abstract:
Since time immemorial, mankind has responded to stories. Recently, anthropologists and scientistsรขโฌโfrom Joseph Campbell to Randy Olsenรขโฌโhave tasked themselves with exploring the fundamental structures of stories, uncovering story types and patterns that repeat across the centuries. Film-makers and novelists have used these to tremendous effect, harnessing the power of the hero's journey to create unforgettable narratives. Yet scientists, by contrast, have been slow on the uptake.
In this event, Prof. Alison Woollard talks about the science of storytelling and storytelling in science. A Royal Institution Trustee who gave the iconic Christmas Lectures, she touches on the neuroscience of learning, the role of story in primitive cultures and the structure of story. Moreover, she argues that story is a crucial ingredient in communicating scientific discovery, which we hold as a core belief at the London Institute.
The event is in our 2nd-floor seminar room in the Royal Institution. After introductory drinks at 5:00, the talk starts at 5.30, followed by drinks and discussion afterwards. RSVP at smc@lims.ac.uk.
Since time immemorial, mankind has responded to stories. Recently, anthropologists and scientistsรขโฌโfrom Joseph Campbell to Randy Olsenรขโฌโhave tasked themselves with exploring the fundamental structures of stories, uncovering story types and patterns that repeat across the centuries. Film-makers and novelists have used these to tremendous effect, harnessing the power of the hero's journey to create unforgettable narratives. Yet scientists, by contrast, have been slow on the uptake.
In this event, Prof. Alison Woollard talks about the science of storytelling and storytelling in science. A Royal Institution Trustee who gave the iconic Christmas Lectures, she touches on the neuroscience of learning, the role of story in primitive cultures and the structure of story. Moreover, she argues that story is a crucial ingredient in communicating scientific discovery, which we hold as a core belief at the London Institute.
The event is in our 2nd-floor seminar room in the Royal Institution. After introductory drinks at 5:00, the talk starts at 5.30, followed by drinks and discussion afterwards. RSVP at smc@lims.ac.uk.
Posted by: oxford
Thu
9 Dec 2021
Some Quantum States of M-Branes under Hypothesis H
Urs Schreiber
(CAS Prague)
Abstract:
[there will be a pre-seminar for students at 13:30. For zoom link please email s.nagy@qmul.ac.uk]
Following a proposal by H. Sati, we have recently stated a hypothesis
about the mathematical home of the quantum charges in M-theory. This
รขโฌลHypothesis Hรขโฌย refines the traditional proposal for quantization of
D-brane charge from K-theory to the non-abelian cohomology theory
known as 4-Cohomotopy, whose classifying space is the 4-sphere.
Besides its motivation from homotopy-theoretic re-analysis of 11d
supergravity and of the old brane scan, Hypothesis H is currently
justified by its rigorous implication of a list of long-conjectured
M-theoretic consistency conditions on C-field flux and M-brane charges
รขโฌโ such as shifted C-field flux quantization, dual Page charge
quantization and M2/M5-brane tadpole cancellation.
But if Hypothesis H is a correct assumption about the nature of
M-theory, this suggests that quantum states of full M-theory should be
reflected in the positive cohomology of the moduli space of Cohomotopy
cocycles, much like quantum states of non-perturbative Chern-Simons
theory are in the Dolbeault cohomology of moduli spaces of (flat)
connections.
In this talk I discuss how, in the topological sector of D6/D8-brane
intersections, such quantum states according to Hypothesis H are
identified with *weight systems* on *horizontal chord diagrams*, and
how these do reflect a range of phenomena expected from the
traditional approaches to understanding these brane intersections,
such as non-abelian DBI-theory, the BMN matrix model, Rozansky-Witten
theory and Hanany-Witten theory.
Specifically, we have proven that the sl(2,C)-weight system satisfies
the positivity condition that characterizes physical (i.e. non-ghost)
quantum states. Under the above identification, this quantum state
corresponds to an elementary fuzzy funnel configuration and/or to the
elementary transverse M5-brane state in the BMN matrix model รขโฌโ both as
expected for D6/D8-brane intersections.
Besides possible implications for the elusive formulation of M-theory,
this result may provide a unifying explanation for the plethora of
unexpected appearances that chord diagrams are recently making in
fundamental high energy physics, notably in discussion of holographic
entanglement entropy.
Slides and further pointers available at:
https://ncatlab.org/schreiber/show/Some+Quantum+States+of+M-Branes+under+Hypothesis+H
[there will be a pre-seminar for students at 13:30. For zoom link please email s.nagy@qmul.ac.uk]
Following a proposal by H. Sati, we have recently stated a hypothesis
about the mathematical home of the quantum charges in M-theory. This
รขโฌลHypothesis Hรขโฌย refines the traditional proposal for quantization of
D-brane charge from K-theory to the non-abelian cohomology theory
known as 4-Cohomotopy, whose classifying space is the 4-sphere.
Besides its motivation from homotopy-theoretic re-analysis of 11d
supergravity and of the old brane scan, Hypothesis H is currently
justified by its rigorous implication of a list of long-conjectured
M-theoretic consistency conditions on C-field flux and M-brane charges
รขโฌโ such as shifted C-field flux quantization, dual Page charge
quantization and M2/M5-brane tadpole cancellation.
But if Hypothesis H is a correct assumption about the nature of
M-theory, this suggests that quantum states of full M-theory should be
reflected in the positive cohomology of the moduli space of Cohomotopy
cocycles, much like quantum states of non-perturbative Chern-Simons
theory are in the Dolbeault cohomology of moduli spaces of (flat)
connections.
In this talk I discuss how, in the topological sector of D6/D8-brane
intersections, such quantum states according to Hypothesis H are
identified with *weight systems* on *horizontal chord diagrams*, and
how these do reflect a range of phenomena expected from the
traditional approaches to understanding these brane intersections,
such as non-abelian DBI-theory, the BMN matrix model, Rozansky-Witten
theory and Hanany-Witten theory.
Specifically, we have proven that the sl(2,C)-weight system satisfies
the positivity condition that characterizes physical (i.e. non-ghost)
quantum states. Under the above identification, this quantum state
corresponds to an elementary fuzzy funnel configuration and/or to the
elementary transverse M5-brane state in the BMN matrix model รขโฌโ both as
expected for D6/D8-brane intersections.
Besides possible implications for the elusive formulation of M-theory,
this result may provide a unifying explanation for the plethora of
unexpected appearances that chord diagrams are recently making in
fundamental high energy physics, notably in discussion of holographic
entanglement entropy.
Slides and further pointers available at:
https://ncatlab.org/schreiber/show/Some+Quantum+States+of+M-Branes+under+Hypothesis+H
Posted by: QMW
Thu
9 Dec 2021
Bosonic string from Beltrami Chern-Simons
Roland Bittleston
(Perimeter Institute)
Abstract:
It is well understood how the 2d free scalar CFT emerges from 3d Chern-Simons theory with chiral boundary conditions. Adapting a recent proposal of Costello and Stefanski, I will show how bosonic string theory can be obtained from this description by coupling to a dynamical Beltrami differential in the 3d theory. In particular, I will show how this Beltrami differential restores worldsheet diffeomorphism and Weyl invariance in the 2d theory, and recover the Polyakov action explicitly. By rewriting the theory in the BV formalism, I will show how the bc ghost system arises from the 3d perspective. Finally, if there is sufficient time, I will provide the 3d realization of vertex operators. This talk is based on work in progress with Kevin Costello and Bogdan Stefanski. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
It is well understood how the 2d free scalar CFT emerges from 3d Chern-Simons theory with chiral boundary conditions. Adapting a recent proposal of Costello and Stefanski, I will show how bosonic string theory can be obtained from this description by coupling to a dynamical Beltrami differential in the 3d theory. In particular, I will show how this Beltrami differential restores worldsheet diffeomorphism and Weyl invariance in the 2d theory, and recover the Polyakov action explicitly. By rewriting the theory in the BV formalism, I will show how the bc ghost system arises from the 3d perspective. Finally, if there is sufficient time, I will provide the 3d realization of vertex operators. This talk is based on work in progress with Kevin Costello and Bogdan Stefanski. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
8 Dec 2021
On-shell bootstrap of a general spontaneously broken gauge theory
Zhewei Yin
(Uppsala U.)
Abstract:
It is well known that the most general renormalizable quantum field theory one can write down for a finite spectrum of spin-0, 1/2, and 1 particles is a gauge theory, with possible spontaneously broken symmetries. The existence of Lie group structures in such a theory is dictated by perturbative unitarity of the on-shell scattering amplitudes. Armed with new tools developed for scattering amplitudes, we demonstrate very explicitly how broken symmetries emerge from the constraints of tree unitarity. We review the on-shell spinor helicity formalism, using which we enumerate all possible 3-pt and 4-pt tree amplitudes of massive spin-0, 1/2 and 1 particles satisfying unitarity constraints. We show in these amplitudes how massive vectors and scalars need to be in the same representation of some Lie group, and how the longitudinal components of these massive vectors are equivalent to scalars in the high energy limit. We will also comment on an extended color-kinematics duality that can be hiding in such a general theory.
It is well known that the most general renormalizable quantum field theory one can write down for a finite spectrum of spin-0, 1/2, and 1 particles is a gauge theory, with possible spontaneously broken symmetries. The existence of Lie group structures in such a theory is dictated by perturbative unitarity of the on-shell scattering amplitudes. Armed with new tools developed for scattering amplitudes, we demonstrate very explicitly how broken symmetries emerge from the constraints of tree unitarity. We review the on-shell spinor helicity formalism, using which we enumerate all possible 3-pt and 4-pt tree amplitudes of massive spin-0, 1/2 and 1 particles satisfying unitarity constraints. We show in these amplitudes how massive vectors and scalars need to be in the same representation of some Lie group, and how the longitudinal components of these massive vectors are equivalent to scalars in the high energy limit. We will also comment on an extended color-kinematics duality that can be hiding in such a general theory.
Posted by: QMW
Wed
8 Dec 2021
Holographic Duals of Argyres-Douglas Theories
๐ London
Emily Nardoni
(Kavli IPMU)
Abstract:
The strongly coupled Argyres-Douglas field theories have particular significance among four-dimensional N=2 SCFTs. In this talk, we describe new AdS5 solutions in 11d supergravity and identify them as the gravity duals of a large class of Argyres-Douglas theories, engineered via a stack of M5-branes wrapping a sphere. A notable feature of the gravity solutions is an internal M5-brane source, which is dual to an irregular puncture on the sphere. We explain how the holographic data (including central charges) match the data of the dual Argyres-Douglas field theories
The strongly coupled Argyres-Douglas field theories have particular significance among four-dimensional N=2 SCFTs. In this talk, we describe new AdS5 solutions in 11d supergravity and identify them as the gravity duals of a large class of Argyres-Douglas theories, engineered via a stack of M5-branes wrapping a sphere. A notable feature of the gravity solutions is an internal M5-brane source, which is dual to an irregular puncture on the sphere. We explain how the holographic data (including central charges) match the data of the dual Argyres-Douglas field theories
Posted by: andrea
Wed
8 Dec 2021
TBA
Andreas Schachner
Tue
7 Dec 2021
The twistor origin of hidden w-infinity symmetries in celestial gravity
Lionel Mason
(University of Oxford)
Abstract:
Recently in their celestial holography programme, Strominger and coworkers attempt to provide a holographic description of conventional 4d gravity. In their investigations, they uncovered a hidden w-infinity symmetry in their `celestial soft OPEs' for graviton scattering. This talk will explain the origin of this symmetry in terms of old ideas of Newman and Penrose based on light-cone cuts of null infinity and their description in terms of asymptotic twistors and certain sigma models in asymptotic twistor space. W_n symmetries were introduced by Zamolodchikov as higher spin symmetries in 2d conformal field theories. These were given a geometric interpretation for n=infinity as area-preserving diffeomorphisms of the plane. I will explain how the corresponding loop algebra becomes a hidden symmetry of self-dual gravity via Penrose's nonlinear graviton construction. The action of this symmetry on the tree-level S-matrix of full gravity beyond the self-dual sector will then be obtained from its action on a sigma model in the asymtotic twistor space of a general space-time. This talk is based on https://arxiv.org/abs/2110.06066 and https://arxiv.org/abs/2103.16984.
Recently in their celestial holography programme, Strominger and coworkers attempt to provide a holographic description of conventional 4d gravity. In their investigations, they uncovered a hidden w-infinity symmetry in their `celestial soft OPEs' for graviton scattering. This talk will explain the origin of this symmetry in terms of old ideas of Newman and Penrose based on light-cone cuts of null infinity and their description in terms of asymptotic twistors and certain sigma models in asymptotic twistor space. W_n symmetries were introduced by Zamolodchikov as higher spin symmetries in 2d conformal field theories. These were given a geometric interpretation for n=infinity as area-preserving diffeomorphisms of the plane. I will explain how the corresponding loop algebra becomes a hidden symmetry of self-dual gravity via Penrose's nonlinear graviton construction. The action of this symmetry on the tree-level S-matrix of full gravity beyond the self-dual sector will then be obtained from its action on a sigma model in the asymtotic twistor space of a general space-time. This talk is based on https://arxiv.org/abs/2110.06066 and https://arxiv.org/abs/2103.16984.
Posted by: QMW
Tue
7 Dec 2021
Probing the Physics of Inflation with Gravitational Wave Experiments
Gianmassimo Tasinato
(Swansea )
Abstract:
Cosmological inflation predicts the existence of a stochastic background of gravitational waves (GW), whose features depend on the model of inflation under consideration. There exist well motivated frameworks leading to an enhancement of the primordial GW spectrum at frequency scales testable with GW experiments, with specific features as parity violation, anisotropies, and non-Gaussianity. I will explain the properties of such scenarios, and their distinctive predictions for what respect GW observables. I will then discuss perspectives for testing these predictions with future GW experiments.
Cosmological inflation predicts the existence of a stochastic background of gravitational waves (GW), whose features depend on the model of inflation under consideration. There exist well motivated frameworks leading to an enhancement of the primordial GW spectrum at frequency scales testable with GW experiments, with specific features as parity violation, anisotropies, and non-Gaussianity. I will explain the properties of such scenarios, and their distinctive predictions for what respect GW observables. I will then discuss perspectives for testing these predictions with future GW experiments.
Posted by: IC
Thu
2 Dec 2021
D-branes in AdS3 x S3 x T4 at k=1 and their holographic duals
Jakub Vosmera
(ETH Zurich)
Abstract:
Following the recent work of Eberhardt, Gaberdiel and Gopakumar, exact comparison between various quantities living on the two sides of the AdS/CFT duality has become a possibility. The goal of this talk will be to extend the existing holographic dictionary to include some non-perturbative vacua on both sides. I will start by reviewing the original, purely closed-string setup, giving arguments that string theory on AdS3 x S3 x T4 with minimal k=1 NS-NS flux is exactly dual to the symmetric-product orbifold CFT with the T4 as the seed. I will then construct various D-branes of this string theory and calculate their associated cylinder amplitudes. We will observe that these amplitudes match with the cylinder correlators of certain boundary states of the dual CFT, thus suggesting a direct correspondence between these boundary conditions. I will also show that the disk amplitudes of these D-branes localise to those points in the worldsheet moduli space where the worldsheet disk holomorphically covers the spacetime disk. This talk is based on https://arxiv.org/abs/2110.05509. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Following the recent work of Eberhardt, Gaberdiel and Gopakumar, exact comparison between various quantities living on the two sides of the AdS/CFT duality has become a possibility. The goal of this talk will be to extend the existing holographic dictionary to include some non-perturbative vacua on both sides. I will start by reviewing the original, purely closed-string setup, giving arguments that string theory on AdS3 x S3 x T4 with minimal k=1 NS-NS flux is exactly dual to the symmetric-product orbifold CFT with the T4 as the seed. I will then construct various D-branes of this string theory and calculate their associated cylinder amplitudes. We will observe that these amplitudes match with the cylinder correlators of certain boundary states of the dual CFT, thus suggesting a direct correspondence between these boundary conditions. I will also show that the disk amplitudes of these D-branes localise to those points in the worldsheet moduli space where the worldsheet disk holomorphically covers the spacetime disk. This talk is based on https://arxiv.org/abs/2110.05509. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
1 Dec 2021
tba
Hongliang Jiang
Wed
1 Dec 2021
Royal Institution Lecture: Theory of Everything
Yang-Hui He
(London Institute, Ri and City, University of London)
Abstract:
To many people, the phrase รขโฌลthe theory of everythingรขโฌย conjures memories of the Oscar-winning film about the life and science of Prof. Stephen Hawking. Yet the quest referred to in that title goes back much further. It is nothing less than the search for the holy grail of science: an elegant unified theory, encompassing all matter, forces and space-time itself. It stretches from Galileo and Newton, via Einstein and Dirac, to the most recent advances in superstring theory.
In this event, Prof. Yang-Hui He presents the story as a dance of discovery between data, physics and mathematics, each anticipating the otherรขโฌโขs moves. They have all taken the lead at different times, yet for many today, including Prof. He, the guiding principle is the rigour and beauty of mathematics. It is fitting that this event is held at the Royal Institution, where Faraday uncovered the principles of electromagnetism. These inspired Maxwell's equations, a key component of any unifying theory.
To many people, the phrase รขโฌลthe theory of everythingรขโฌย conjures memories of the Oscar-winning film about the life and science of Prof. Stephen Hawking. Yet the quest referred to in that title goes back much further. It is nothing less than the search for the holy grail of science: an elegant unified theory, encompassing all matter, forces and space-time itself. It stretches from Galileo and Newton, via Einstein and Dirac, to the most recent advances in superstring theory.
In this event, Prof. Yang-Hui He presents the story as a dance of discovery between data, physics and mathematics, each anticipating the otherรขโฌโขs moves. They have all taken the lead at different times, yet for many today, including Prof. He, the guiding principle is the rigour and beauty of mathematics. It is fitting that this event is held at the Royal Institution, where Faraday uncovered the principles of electromagnetism. These inspired Maxwell's equations, a key component of any unifying theory.
Posted by: oxford
November 2021
Tue
30 Nov 2021
Quasi-Normal Modes of Black-Holes and Branes from Quantum Seiberg-Witten Curves
Massimo Bianchi
(Universita degli studi di Roma Tor Vergata)
Abstract:
After reviewing the role Quasi-Normal Modes (QNMs) play in the
Gravitational Wave (GW) signals emitted in the ring-down phase of
Black-Hole (BH) mergers, we present a novel efficient approach to
compute QNMs of BHs, D-branes and fuzz-balls, based on quantum
Seiberg-Witten (SW) curves for N=2 supersymmetric Yang-Mills (SYM)
theories. We find remarkable agreement with numerical results obtained
by means of Leaver's method of continuous fractions and with
`semi-classical' results obtained in the eikonal approximation, based on
geodetic motion. Finally we discuss the extension to D3-branes and their
bound states of Couch-Torrence (CT) conformal inversions, that exchange
horizon and infinity, and show that they keep the photon-sphere (or
photon-halo) fixed.
After reviewing the role Quasi-Normal Modes (QNMs) play in the
Gravitational Wave (GW) signals emitted in the ring-down phase of
Black-Hole (BH) mergers, we present a novel efficient approach to
compute QNMs of BHs, D-branes and fuzz-balls, based on quantum
Seiberg-Witten (SW) curves for N=2 supersymmetric Yang-Mills (SYM)
theories. We find remarkable agreement with numerical results obtained
by means of Leaver's method of continuous fractions and with
`semi-classical' results obtained in the eikonal approximation, based on
geodetic motion. Finally we discuss the extension to D3-branes and their
bound states of Couch-Torrence (CT) conformal inversions, that exchange
horizon and infinity, and show that they keep the photon-sphere (or
photon-halo) fixed.
Posted by: IC
Thu
25 Nov 2021
London Integrability Journal Club Gong Show
Many Speakers
(various places)
Abstract:
We will have a new edition of the London Integrability Journal Club Gong Show, with six 10+5 mins talks by:
Meer Ashwinkumar, Kavli Inst. Tokyo, "Three-dimensional WZW model and the R-matrix of the Yangian".
Carlos Bercini, ICTP-SAIFR, "The Wilson Loop - Large Spin OPE Dictionary".
Aleix Gimenez-Grau, DESY, "Bootstrapping holographic defect correlators".
Himanshu Khanchandani, Princeton Univ., "CFT in AdS and Gross-Neveu BCFT".
Levente Pristyak, Budapest Univ., "Current operators in the XYZ model".
Xinyu Zhang, DESY, "Hidden symmetry in 4d N=2 quiver gauge theory".
Abstracts and schedule can be found on the LIJC website, integrability-london.weebly.com . If you are not registered, please email Andrea Cavaglia at KCL for the Zoom link.
We will have a new edition of the London Integrability Journal Club Gong Show, with six 10+5 mins talks by:
Meer Ashwinkumar, Kavli Inst. Tokyo, "Three-dimensional WZW model and the R-matrix of the Yangian".
Carlos Bercini, ICTP-SAIFR, "The Wilson Loop - Large Spin OPE Dictionary".
Aleix Gimenez-Grau, DESY, "Bootstrapping holographic defect correlators".
Himanshu Khanchandani, Princeton Univ., "CFT in AdS and Gross-Neveu BCFT".
Levente Pristyak, Budapest Univ., "Current operators in the XYZ model".
Xinyu Zhang, DESY, "Hidden symmetry in 4d N=2 quiver gauge theory".
Abstracts and schedule can be found on the LIJC website, integrability-london.weebly.com . If you are not registered, please email Andrea Cavaglia at KCL for the Zoom link.
Posted by: andrea
Wed
24 Nov 2021
Conformal bootstrap meets cosmology
๐ London
Matthijs Hogervorst
(EPFL)
Abstract:
Local observables in a de Sitter universe become conformal, if you wait long enough. Indeed, one can study the imprints of inflation by looking at conformal correlations in the sky. Thereรขโฌโขs an ongoing effort in the cosmology community to understand these late-time correlators from first principles, without invoking a specific Lagrangian.
In this talk, I will discuss the late-time CFT living in de Sitter through the lens of a quantum field theorist. The CFT in question shares many features with its counterparts in flat space or AdS, but differs in crucial aspects: in particular, it can have complex scaling dimensions and correlation functions. I will nevertheless argue that de Sitter CFTs have good unitarity properties and can be constrained via conformal bootstrap equations. This observation should open up a new way to constrain cosmological correlation functions.
Local observables in a de Sitter universe become conformal, if you wait long enough. Indeed, one can study the imprints of inflation by looking at conformal correlations in the sky. Thereรขโฌโขs an ongoing effort in the cosmology community to understand these late-time correlators from first principles, without invoking a specific Lagrangian.
In this talk, I will discuss the late-time CFT living in de Sitter through the lens of a quantum field theorist. The CFT in question shares many features with its counterparts in flat space or AdS, but differs in crucial aspects: in particular, it can have complex scaling dimensions and correlation functions. I will nevertheless argue that de Sitter CFTs have good unitarity properties and can be constrained via conformal bootstrap equations. This observation should open up a new way to constrain cosmological correlation functions.
Posted by: andrea
Wed
24 Nov 2021
How well do we know the SMEFT, and how to learn more
Veronica Sanz
(University of Valencia)
Abstract:
[there will be a pre-seminar for students at 1.30PM; for zoom link please email s.nagy@qmul.ac.uk]
The characterization of measurements using the EFT framework is becoming prevalent, not just in its traditional realm of low-energy physics, but now also with LHC high-energy probes. At the LHC, the EFT approach is viewed as a way to transcend models, to exploit the huge range of LHC topologies, and even as a form of data preservation. In this talk we will review this state-of-affairs, point out challenges with this approach and also discuss some new opportunities that more data will bring.
[there will be a pre-seminar for students at 1.30PM; for zoom link please email s.nagy@qmul.ac.uk]
The characterization of measurements using the EFT framework is becoming prevalent, not just in its traditional realm of low-energy physics, but now also with LHC high-energy probes. At the LHC, the EFT approach is viewed as a way to transcend models, to exploit the huge range of LHC topologies, and even as a form of data preservation. In this talk we will review this state-of-affairs, point out challenges with this approach and also discuss some new opportunities that more data will bring.
Posted by: QMW
Wed
24 Nov 2021
tba
Emanuel Malek
Tue
23 Nov 2021
The Higgs mass, UV/IR mixing and the effective field theory from a string perspective.
Steve Abel
(Durham)
Abstract:
Almost all existing calculations that concern the Higgs mass are performed within the framework of an effective field theory. While sufficient for certain purposes, such calculations throw up problems to do with fine-tuning and naturalness in particular the famous hierarchy problem. This makes most attempts within field theory to understand the Higgs mass pretty much futile. Even most phenomenology done within string theory does not respect the full string symmetries that are responsible for many of the remarkable finiteness properties for which string theory is famous. Chief among these symmetries is worldsheet modular invariance, which is an exact symmetry of all perturtubative closed-string vacua. And yet if the UV is tamed by this symmetry then it should be exact even today! In this talk I will discuss the many things one can learn from this fact. For example that a gravitational modular anomaly generically relates the Higgs mass to the one-loop cosmological constant, yielding a string-theoretic connection between the two fundamental quantities which are known to suffer from hierarchy problems in the absence of spacetime supersymmetry. In addition one learns about the use and interpretation of modular invariant regulators in string theory, which in turn dictates how string theory arranges its UV/IR-mixing to make itself finite. Finally, I discuss how the effective field theory emerges showing that ultimately the Higgs mass can be understood as arising from an infinite รขโฌลstringyรขโฌย sum of Coleman-Weinberg effective potentials in such theories. The results can therefore serve as the launching point for a rigorous investigation of hierarchy problems in a UV complete theory.
Almost all existing calculations that concern the Higgs mass are performed within the framework of an effective field theory. While sufficient for certain purposes, such calculations throw up problems to do with fine-tuning and naturalness in particular the famous hierarchy problem. This makes most attempts within field theory to understand the Higgs mass pretty much futile. Even most phenomenology done within string theory does not respect the full string symmetries that are responsible for many of the remarkable finiteness properties for which string theory is famous. Chief among these symmetries is worldsheet modular invariance, which is an exact symmetry of all perturtubative closed-string vacua. And yet if the UV is tamed by this symmetry then it should be exact even today! In this talk I will discuss the many things one can learn from this fact. For example that a gravitational modular anomaly generically relates the Higgs mass to the one-loop cosmological constant, yielding a string-theoretic connection between the two fundamental quantities which are known to suffer from hierarchy problems in the absence of spacetime supersymmetry. In addition one learns about the use and interpretation of modular invariant regulators in string theory, which in turn dictates how string theory arranges its UV/IR-mixing to make itself finite. Finally, I discuss how the effective field theory emerges showing that ultimately the Higgs mass can be understood as arising from an infinite รขโฌลstringyรขโฌย sum of Coleman-Weinberg effective potentials in such theories. The results can therefore serve as the launching point for a rigorous investigation of hierarchy problems in a UV complete theory.
Posted by: IC
Mon
22 Nov 2021
Lonti: Duality Symmetry in String Theory
Chris Hull
(IC)
Abstract:
Live Tutorial.
This lecture provides an introduction to duality symmetries in string theory.
String theory was originally formulated as a theory of strings propagating in space time with interactions governed by the string coupling constant g. Scattering amplitudes for small g were constructed as a perturbation theory in g. Five consistent supersymmetric string theories were found, all in 10 spacetime dimensions with five distinct perturbation theories. This left many questions unanswered, such as why there should be five apparently consistent quantum theories of gravity and what happens to these theories as the coupling constant is increased.
Such questions were answered by the developments in the mid-1990s that have been called the 2nd superstring revolution. Dualities proved to be the key to uncovering the non-perturbative structure of superstring theory and in particular its strong coupling behaviour. When g is large, one can analyse the theory as a perturbation theory in 1/g and seek a "dual theory" with coupling constant g' whose perturbative expansion in g' matches the behaviour of the original theory as a perturbation theory in 1/g on identifying g'=1/g. In some cases the dual theory is again a string theory, which might be a different string theory from the original one. In other cases, the dual theory isn't a string theory at all, but a new theory - M-theory. This leads to a picture in which all 5 string theories are related by dualities and so are all seen as different limits of M-theory. Duality transformation provide new symmetries of string/M theory and T,S and U-dualities. Remarkably, the theory that emerges is no longer just a theory of strings but one which includes both strings and branes which are higher dimensional extended objects. As the branes are related to strings by duality symmetries, they should be regarded as being on the same footing as the strings and of equal importance.
The lecture explores all of these issues and discusses some examples.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Live Tutorial.
This lecture provides an introduction to duality symmetries in string theory.
String theory was originally formulated as a theory of strings propagating in space time with interactions governed by the string coupling constant g. Scattering amplitudes for small g were constructed as a perturbation theory in g. Five consistent supersymmetric string theories were found, all in 10 spacetime dimensions with five distinct perturbation theories. This left many questions unanswered, such as why there should be five apparently consistent quantum theories of gravity and what happens to these theories as the coupling constant is increased.
Such questions were answered by the developments in the mid-1990s that have been called the 2nd superstring revolution. Dualities proved to be the key to uncovering the non-perturbative structure of superstring theory and in particular its strong coupling behaviour. When g is large, one can analyse the theory as a perturbation theory in 1/g and seek a "dual theory" with coupling constant g' whose perturbative expansion in g' matches the behaviour of the original theory as a perturbation theory in 1/g on identifying g'=1/g. In some cases the dual theory is again a string theory, which might be a different string theory from the original one. In other cases, the dual theory isn't a string theory at all, but a new theory - M-theory. This leads to a picture in which all 5 string theories are related by dualities and so are all seen as different limits of M-theory. Duality transformation provide new symmetries of string/M theory and T,S and U-dualities. Remarkably, the theory that emerges is no longer just a theory of strings but one which includes both strings and branes which are higher dimensional extended objects. As the branes are related to strings by duality symmetries, they should be regarded as being on the same footing as the strings and of equal importance.
The lecture explores all of these issues and discusses some examples.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Posted by: pethybridge
Mon
22 Nov 2021
Quantum Black Holes and (Mock) Modularity – An encounter between Ramanujan and Hawking
๐ London
Atish Dabholkar
(ICTP)
Abstract:
Mathematical ideas introduced by Ramanujan a century ago in number theory and combinatorics have come to play a surprising role in understanding some deep and fundamental aspects of quantum gravity and quantum field theory in three very distinct contexts of holography, duality, and topology.
In this colloquium, I shall first describe the fascinating history, physics, and mathematics behind this rich and fruitful connection focusing on the role (mock) modular forms have come to play in understanding quantum properties of black holes in string theory. I shall then elucidate briefly the manifestations of mock modularity in physics in its other avatars.
Mathematical ideas introduced by Ramanujan a century ago in number theory and combinatorics have come to play a surprising role in understanding some deep and fundamental aspects of quantum gravity and quantum field theory in three very distinct contexts of holography, duality, and topology.
In this colloquium, I shall first describe the fascinating history, physics, and mathematics behind this rich and fruitful connection focusing on the role (mock) modular forms have come to play in understanding quantum properties of black holes in string theory. I shall then elucidate briefly the manifestations of mock modularity in physics in its other avatars.
Posted by: andrea
Thu
18 Nov 2021
Classification of topological quantum field theories
Theo Johnson-Freyd
(Perimeter Inst. Theor. Phys.)
Abstract:
Modulo some vitally important ansรยคtze, subtleties, provisos, and work in progress, all topological quantum field theories are gauge theories for higher finite groups. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Modulo some vitally important ansรยคtze, subtleties, provisos, and work in progress, all topological quantum field theories are gauge theories for higher finite groups. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
18 Nov 2021
Correlation functions of twist fields from hydrodynamics
Benjamin Doyon
(King's College London)
Abstract:
The Euler-scale power-law asymptotics of space-time correlation functions in many-body systems, quantum and classical, can be obtained by projecting the observables onto the hydrodynamic modes admitted by the model and state. This is the Boltzmann-Gibbs principle; it works for integrable and non-integrable models alike. However, certain observables, such as some order parameters in thermal of generalised Gibbs ensembles, do not couple to any hydrodynamic mode: the Boltzmann-Gibbs principle gives zero. I will explain how hydrodynamics can still give the leading exponential decay of order parameter correlation functions. With the examples of the quantum XX chain and the sine-Gordon model, I will explain how large deviations of the spin and U(1) current fluctuations are related to such exponential decay. Exact predictions are given by the ballistic fluctuation theory based on generalised hydrodynamics. In the XX model, this is in agreement with results obtained previously by a more involved Fredholm determinant analysis and other techniques, and even gives a new formula for a parameter regime not hitherto studied. In the sine-Gordon model, these are new results, inaccessible by other techniques. Works in collaboration with Giuseppe Del Vecchio Del Vecchio, and Mรยกrton Kormos. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
The Euler-scale power-law asymptotics of space-time correlation functions in many-body systems, quantum and classical, can be obtained by projecting the observables onto the hydrodynamic modes admitted by the model and state. This is the Boltzmann-Gibbs principle; it works for integrable and non-integrable models alike. However, certain observables, such as some order parameters in thermal of generalised Gibbs ensembles, do not couple to any hydrodynamic mode: the Boltzmann-Gibbs principle gives zero. I will explain how hydrodynamics can still give the leading exponential decay of order parameter correlation functions. With the examples of the quantum XX chain and the sine-Gordon model, I will explain how large deviations of the spin and U(1) current fluctuations are related to such exponential decay. Exact predictions are given by the ballistic fluctuation theory based on generalised hydrodynamics. In the XX model, this is in agreement with results obtained previously by a more involved Fredholm determinant analysis and other techniques, and even gives a new formula for a parameter regime not hitherto studied. In the sine-Gordon model, these are new results, inaccessible by other techniques. Works in collaboration with Giuseppe Del Vecchio Del Vecchio, and Mรยกrton Kormos. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
17 Nov 2021
Superspin chains from superstring theory
Faroogh Moosavian
Abstract:
The Bethe-Gauge Correspondence (BGC) of Nekrasov and Shatashvili, which relates 1d quantum integrable spin chains to two-dimensional supersymmetric gauge theories with \mathcal{N}=2 supersymmetry, is one of the instances of the deep connection between supersymmetric gauge theories and integrable models. The question that will be the main content of the talk is the origin of this correspondence. I will explain how the BGC could be naturally realized within superstring theory. Toward this aim, I will first explain The Bethe Side (noncompact rational integrable \mathfrak{gl}(m|n) superspin chains) and the corresponding Gauge Side of the BGC. I will then discuss the brane setup for the realization of The Gauge Side. Using string dualities, this brane setup will be mapped to another setup, which realizes The Bethe Side of the correspondence. An important role in this duality frame is played by the 4d Chern-Simons Theory of Costello which explains the integrability of The Bethe Side. If time permits, I will also explain the story for the compact rational integrable \mathfrak{gl}(m|n) superspin chains. This talk is based on the joint work (arXiv:2110.15112) with Nafiz Ishtiaque, Surya Raghavendran, and Junya Yagi.
The Bethe-Gauge Correspondence (BGC) of Nekrasov and Shatashvili, which relates 1d quantum integrable spin chains to two-dimensional supersymmetric gauge theories with \mathcal{N}=2 supersymmetry, is one of the instances of the deep connection between supersymmetric gauge theories and integrable models. The question that will be the main content of the talk is the origin of this correspondence. I will explain how the BGC could be naturally realized within superstring theory. Toward this aim, I will first explain The Bethe Side (noncompact rational integrable \mathfrak{gl}(m|n) superspin chains) and the corresponding Gauge Side of the BGC. I will then discuss the brane setup for the realization of The Gauge Side. Using string dualities, this brane setup will be mapped to another setup, which realizes The Bethe Side of the correspondence. An important role in this duality frame is played by the 4d Chern-Simons Theory of Costello which explains the integrability of The Bethe Side. If time permits, I will also explain the story for the compact rational integrable \mathfrak{gl}(m|n) superspin chains. This talk is based on the joint work (arXiv:2110.15112) with Nafiz Ishtiaque, Surya Raghavendran, and Junya Yagi.
Posted by: IC
Wed
17 Nov 2021
Boundary criticality of the O(N) model in d = 3 critically revisited
๐ London
Maxim Metlitski
(MIT)
Abstract:
It is known that the classical O(N) model in dimension d > 3 at its bulk critical point admits three boundary universality classes: the ordinary, the extraordinary and the special. The extraordinary fixed point corresponds to the bulk transition occurring in the presence of an ordered boundary, while the special fixed point corresponds to a boundary phase transition between the ordinary and the extra-ordinary classes. While the ordinary fixed point survives in d = 3, it is less clear what happens to the extraordinary and special fixed points when d = 3 and N is greater or equal to 2. I'll show that formally treating N as a continuous parameter, there exists a finite range 2 < N < N_c where the extra-ordinary universality class survives, albeit in a modified form: the long-range boundary order is lost, instead, the order parameter correlation function decays as a power of log r. I'll discuss recent Monte-Carlo simulations and numerical bootstrap results that confirm the above picture and indicate that the critical value N_c > 3.
Based on arXiv:2009.05119, 2111.03613, 2111.03071
It is known that the classical O(N) model in dimension d > 3 at its bulk critical point admits three boundary universality classes: the ordinary, the extraordinary and the special. The extraordinary fixed point corresponds to the bulk transition occurring in the presence of an ordered boundary, while the special fixed point corresponds to a boundary phase transition between the ordinary and the extra-ordinary classes. While the ordinary fixed point survives in d = 3, it is less clear what happens to the extraordinary and special fixed points when d = 3 and N is greater or equal to 2. I'll show that formally treating N as a continuous parameter, there exists a finite range 2 < N < N_c where the extra-ordinary universality class survives, albeit in a modified form: the long-range boundary order is lost, instead, the order parameter correlation function decays as a power of log r. I'll discuss recent Monte-Carlo simulations and numerical bootstrap results that confirm the above picture and indicate that the critical value N_c > 3.
Based on arXiv:2009.05119, 2111.03613, 2111.03071
Posted by: andrea
Tue
16 Nov 2021
Aspects of Rotating Black Holes in Dynamical Chern-Simons Gravity
Leah Jenks
(Brown University)
Abstract:
In this talk I will give an overview of recent and ongoing work regarding rotating black holes in dynamical Chern-Simons (dCS) gravity. dCS gravity is a well motivated modified theory of gravity which has been extensively studied in gravitational and cosmological contexts. I will first discuss unique geometric structures, `the Chern-Simons caps,' which slowly rotating black holes in dCS gravity were recently found to possess. Motivated by the dCS caps, I will then discuss superradiance in the context of slowly rotating dCS black holes and show that there are corrections to the usual solution for a Kerr black hole. Lastly, I will comment on the observable implications for these corrections and point towards avenues for future work.
In this talk I will give an overview of recent and ongoing work regarding rotating black holes in dynamical Chern-Simons (dCS) gravity. dCS gravity is a well motivated modified theory of gravity which has been extensively studied in gravitational and cosmological contexts. I will first discuss unique geometric structures, `the Chern-Simons caps,' which slowly rotating black holes in dCS gravity were recently found to possess. Motivated by the dCS caps, I will then discuss superradiance in the context of slowly rotating dCS black holes and show that there are corrections to the usual solution for a Kerr black hole. Lastly, I will comment on the observable implications for these corrections and point towards avenues for future work.
Posted by: IC
Mon
15 Nov 2021
Lonti: Duality Symmetry in String Theory
Chris Hull
(IC)
Abstract:
This lecture provides an introduction to duality symmetries in string theory.
String theory was originally formulated as a theory of strings propagating in space time with interactions governed by the string coupling constant g. Scattering amplitudes for small g were constructed as a perturbation theory in g. Five consistent supersymmetric string theories were found, all in 10 spacetime dimensions with five distinct perturbation theories. This left many questions unanswered, such as why there should be five apparently consistent quantum theories of gravity and what happens to these theories as the coupling constant is increased.
Such questions were answered by the developments in the mid-1990s that have been called the 2nd superstring revolution. Dualities proved to be the key to uncovering the non-perturbative structure of superstring theory and in particular its strong coupling behaviour. When g is large, one can analyse the theory as a perturbation theory in 1/g and seek a "dual theory" with coupling constant g' whose perturbative expansion in g' matches the behaviour of the original theory as a perturbation theory in 1/g on identifying g'=1/g. In some cases the dual theory is again a string theory, which might be a different string theory from the original one. In other cases, the dual theory isn't a string theory at all, but a new theory - M-theory. This leads to a picture in which all 5 string theories are related by dualities and so are all seen as different limits of M-theory. Duality transformation provide new symmetries of string/M theory and T,S and U-dualities. Remarkably, the theory that emerges is no longer just a theory of strings but one which includes both strings and branes which are higher dimensional extended objects. As the branes are related to strings by duality symmetries, they should be regarded as being on the same footing as the strings and of equal importance.
The lecture explores all of these issues and discusses some examples.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
The lecture is available here: https://youtube.com/playlist?list=PLlva4MroG-KHsP0WGLxRk9ZWsmAHUklMT
This lecture provides an introduction to duality symmetries in string theory.
String theory was originally formulated as a theory of strings propagating in space time with interactions governed by the string coupling constant g. Scattering amplitudes for small g were constructed as a perturbation theory in g. Five consistent supersymmetric string theories were found, all in 10 spacetime dimensions with five distinct perturbation theories. This left many questions unanswered, such as why there should be five apparently consistent quantum theories of gravity and what happens to these theories as the coupling constant is increased.
Such questions were answered by the developments in the mid-1990s that have been called the 2nd superstring revolution. Dualities proved to be the key to uncovering the non-perturbative structure of superstring theory and in particular its strong coupling behaviour. When g is large, one can analyse the theory as a perturbation theory in 1/g and seek a "dual theory" with coupling constant g' whose perturbative expansion in g' matches the behaviour of the original theory as a perturbation theory in 1/g on identifying g'=1/g. In some cases the dual theory is again a string theory, which might be a different string theory from the original one. In other cases, the dual theory isn't a string theory at all, but a new theory - M-theory. This leads to a picture in which all 5 string theories are related by dualities and so are all seen as different limits of M-theory. Duality transformation provide new symmetries of string/M theory and T,S and U-dualities. Remarkably, the theory that emerges is no longer just a theory of strings but one which includes both strings and branes which are higher dimensional extended objects. As the branes are related to strings by duality symmetries, they should be regarded as being on the same footing as the strings and of equal importance.
The lecture explores all of these issues and discusses some examples.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
The lecture is available here: https://youtube.com/playlist?list=PLlva4MroG-KHsP0WGLxRk9ZWsmAHUklMT
Posted by: pethybridge
Mon
15 Nov 2021
Lonti: An Introduction to Observables in Gauge Theories
Nadav Drukker
(KCL)
Abstract:
Lonti Autumn 2021 Series: Lecture 4. Live Tutorial.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Gauge theories are ubiquitous in theoretical physics, not to mention that the standard model is one. It is therefore of utmost importance to know what the observables of these theories are, quantities that can be calculated and measured. I start with a long discussion based on the most familiar gauge theory, Maxwell's electromagnetism, where a lot of computations can be done explicitly. I then take the lessons from that to non-abelian gauge theories. The observables covered are local, Wilson loops, and briefly 't Hooft loops and surface operators.
Lonti Autumn 2021 Series: Lecture 4. Live Tutorial.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Gauge theories are ubiquitous in theoretical physics, not to mention that the standard model is one. It is therefore of utmost importance to know what the observables of these theories are, quantities that can be calculated and measured. I start with a long discussion based on the most familiar gauge theory, Maxwell's electromagnetism, where a lot of computations can be done explicitly. I then take the lessons from that to non-abelian gauge theories. The observables covered are local, Wilson loops, and briefly 't Hooft loops and surface operators.
Posted by: pethybridge
Thu
11 Nov 2021
Amplitudes, Loops, and Gravity
Mao Zeng
(Edinburgh)
Abstract:
[for zoom link please email s.nagy@qmul.ac.uk]
Next-generation gravitational wave detectors demand highly precise predictions for waveforms. We present advances in binary inspiral dynamics by taking classical limits of scattering amplitudes in perturbative quantum gravity. The amplitudes are calculated efficiently using modern methods for scattering amplitudes and loop integration techniques developed for colliders. Classical physics can be extracted by several complementary approaches, including effective field theory, eikonal exponentiation, and extrapolation of quantum observables defined by the S-matrix. For both conservative and radiative dynamics, we obtain new terms in the post-Minksowskian expansion which represent first advances in decades.
[for zoom link please email s.nagy@qmul.ac.uk]
Next-generation gravitational wave detectors demand highly precise predictions for waveforms. We present advances in binary inspiral dynamics by taking classical limits of scattering amplitudes in perturbative quantum gravity. The amplitudes are calculated efficiently using modern methods for scattering amplitudes and loop integration techniques developed for colliders. Classical physics can be extracted by several complementary approaches, including effective field theory, eikonal exponentiation, and extrapolation of quantum observables defined by the S-matrix. For both conservative and radiative dynamics, we obtain new terms in the post-Minksowskian expansion which represent first advances in decades.
Posted by: QMW
Thu
11 Nov 2021
Gauged sigma models from four-dimensional Chern-Simons
Jake Stedman
(King's College London)
Abstract:
Several years ago, a new gauge theory called four-dimensional Chern-Simons was introduced by Costello in an attempt to explain the integrability of various two-dimensional models using techniques in gauge theory. My work focuses on the use of four-dimensional Chern-Simons to explain the integrability of two-dimensional sigma models. I will begin by reviewing the construction of the Wess-Zumino-Witten (WZW) model as the boundary theory of three-dimensional Chern-Simons theory as was introduced by Moore and Seiberg. This will allow me to introduce the analogous construction of Costello and Yamazaki, in which two-dimensional sigma models appear as theories on defects in four-dimensional Chern-Simons. This naturally leads to a discussion of my work in which I construct a large class of gauged sigma models by coupling together two four-dimensional Chern-Simons theories. I will argue that the structure of four-dimensional Chern-Simons suggests that these models are integrable and finish by constructing the gauged WZW model and conformal Toda theories. This talk is based on: https://arxiv.org/abs/2109.08101. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Several years ago, a new gauge theory called four-dimensional Chern-Simons was introduced by Costello in an attempt to explain the integrability of various two-dimensional models using techniques in gauge theory. My work focuses on the use of four-dimensional Chern-Simons to explain the integrability of two-dimensional sigma models. I will begin by reviewing the construction of the Wess-Zumino-Witten (WZW) model as the boundary theory of three-dimensional Chern-Simons theory as was introduced by Moore and Seiberg. This will allow me to introduce the analogous construction of Costello and Yamazaki, in which two-dimensional sigma models appear as theories on defects in four-dimensional Chern-Simons. This naturally leads to a discussion of my work in which I construct a large class of gauged sigma models by coupling together two four-dimensional Chern-Simons theories. I will argue that the structure of four-dimensional Chern-Simons suggests that these models are integrable and finish by constructing the gauged WZW model and conformal Toda theories. This talk is based on: https://arxiv.org/abs/2109.08101. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
10 Nov 2021
Phase transitions for deformations of JT supergravity and matrix models
๐ London
G Joaquin Turiaci
(IAS)
Abstract:
We analyze black holes in deformations of Jackiw-Teitelboim (JT) supergravity by adding a gas of defects, equivalent to changing the dilaton potential. For some range of deformations, the black hole density of states extracted from the gravitational path integral becomes negative, yielding an ill-defined sum over topologies. To solve this problem, we use an equivalent matrix model description and show the negative spectrum is resolved via a phase transition analogous to the Gross-Witten transition. The matrix model contains a rich and novel phase structure that we explore in detail, using both perturbative and non-perturbative techniques.
We analyze black holes in deformations of Jackiw-Teitelboim (JT) supergravity by adding a gas of defects, equivalent to changing the dilaton potential. For some range of deformations, the black hole density of states extracted from the gravitational path integral becomes negative, yielding an ill-defined sum over topologies. To solve this problem, we use an equivalent matrix model description and show the negative spectrum is resolved via a phase transition analogous to the Gross-Witten transition. The matrix model contains a rich and novel phase structure that we explore in detail, using both perturbative and non-perturbative techniques.
Posted by: andrea
Wed
10 Nov 2021
Defect Central Charges
Adam Chalabi
(Southampton)
Abstract:
Conformal defects can be characterised by their contributions to the Weyl anomaly. The coefficients of these terms, often called defect central charges, depend on the particular defect insertion in a given conformal field theory. I will review what is currently known about defect central charges across dimensions, and present novel results. I will discuss many examples where they can be computed exactly without requiring any approximations or limits. These include defects in free theories, and recently developed tools for defects in superconformal field theories.
Conformal defects can be characterised by their contributions to the Weyl anomaly. The coefficients of these terms, often called defect central charges, depend on the particular defect insertion in a given conformal field theory. I will review what is currently known about defect central charges across dimensions, and present novel results. I will discuss many examples where they can be computed exactly without requiring any approximations or limits. These include defects in free theories, and recently developed tools for defects in superconformal field theories.
Posted by: IC
Tue
9 Nov 2021
Black holes, information and wormholes
Geoff Penington
(UC Berkeley and IAS)
Abstract:
Hawking famously argued, based on semiclassical calculations, that the radiation from evaporating black holes is contains no information about the matter that fell in. This would be inconsistent with the unitarity of quantum mechanics. In this talk, I will show that, in more careful รขโฌหreplica trickรขโฌโข calculations, the gravitational path integral becomes dominated at late times by saddles containing spacetime wormholes. These wormholes cause the entropy to decrease after the Page time, consistent with unitarity, and allow information to escape from the interior of the black hole.
Hawking famously argued, based on semiclassical calculations, that the radiation from evaporating black holes is contains no information about the matter that fell in. This would be inconsistent with the unitarity of quantum mechanics. In this talk, I will show that, in more careful รขโฌหreplica trickรขโฌโข calculations, the gravitational path integral becomes dominated at late times by saddles containing spacetime wormholes. These wormholes cause the entropy to decrease after the Page time, consistent with unitarity, and allow information to escape from the interior of the black hole.
Posted by: IC
Mon
8 Nov 2021
Lonti: An Introduction to Observables in Gauge Theories
Nadav Drukker
(KCL)
Abstract:
Lonti Autumn 2021 Series: Lecture 4. Release of Recorded Lecture. Available at https://youtu.be/JLbuSnt2OyA.
Gauge theories are ubiquitous in theoretical physics, not to mention that the standard model is one. It is therefore of utmost importance to know what the observables of these theories are, quantities that can be calculated and measured. I start with a long discussion based on the most familiar gauge theory, Maxwell's electromagnetism, where a lot of computations can be done explicitly. I then take the lessons from that to non-abelian gauge theories. The observables covered are local, Wilson loops, and briefly 't Hooft loops and surface operators.
Lonti Autumn 2021 Series: Lecture 4. Release of Recorded Lecture. Available at https://youtu.be/JLbuSnt2OyA.
Gauge theories are ubiquitous in theoretical physics, not to mention that the standard model is one. It is therefore of utmost importance to know what the observables of these theories are, quantities that can be calculated and measured. I start with a long discussion based on the most familiar gauge theory, Maxwell's electromagnetism, where a lot of computations can be done explicitly. I then take the lessons from that to non-abelian gauge theories. The observables covered are local, Wilson loops, and briefly 't Hooft loops and surface operators.
Posted by: pethybridge
Mon
8 Nov 2021
Lonti: CPT symmetry in Quantum Field Theory
Andreas Fring
(City)
Abstract:
Lonti Autumn 2021 Series: Lecture 3. Live Tutorial.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
CPT-symmetry is a fundamental symmetry of nature that is respected by all physical processes. It consists of a consecutive reversal of time (T), reflection of space at an arbitrary point (Parity P) and a charge conjugation that replaces particles by antiparticles. I briefly discuss the role P T -symmetry plays in quantum mechanics and how it may be utilised for a consistent formulation of non-Hermitian theories. For a relativistic quantum field theory the CPT-theorem provides the general framework for the validity of this symmetry to occur, by stating that the CPT-symmetry is equivalent to a strong reflection and a simultaneous Hermitian conjugation. In this lecture I will prove the theory in the framework of a Lagrangian quantum field theory for spin 0, 1 and spin 1/2 Dirac fields, by first identifying the separate transformation and a subsequent combination. Subsequently these transformations are used to identify the behaviour of various interaction terms under their action. I conclude by commenting on the experimental observations of CP-symmetry violation in the neutral K-meson decay.
Lonti Autumn 2021 Series: Lecture 3. Live Tutorial.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
CPT-symmetry is a fundamental symmetry of nature that is respected by all physical processes. It consists of a consecutive reversal of time (T), reflection of space at an arbitrary point (Parity P) and a charge conjugation that replaces particles by antiparticles. I briefly discuss the role P T -symmetry plays in quantum mechanics and how it may be utilised for a consistent formulation of non-Hermitian theories. For a relativistic quantum field theory the CPT-theorem provides the general framework for the validity of this symmetry to occur, by stating that the CPT-symmetry is equivalent to a strong reflection and a simultaneous Hermitian conjugation. In this lecture I will prove the theory in the framework of a Lagrangian quantum field theory for spin 0, 1 and spin 1/2 Dirac fields, by first identifying the separate transformation and a subsequent combination. Subsequently these transformations are used to identify the behaviour of various interaction terms under their action. I conclude by commenting on the experimental observations of CP-symmetry violation in the neutral K-meson decay.
Posted by: pethybridge
Mon
8 Nov 2021
Berry Phases and Complexity as Probes of Bulk Geometry
๐ London
Claire Zukowski
(University of Amsterdam)
Abstract:
I will describe two new quantum information theoretic probes of bulk geometry that access information inaccessible to spacelike geodesics. The first arises from considering a parallel transport process of modular Hamiltonians on the boundary under a change of state. I will show that the Berry curvature for this process computes the entanglement wedge symplectic form associated to a family of Euclidean cosmic brane solutions. Next, I will derive the circuit complexity for conformal field theory in arbitrary dimensions. I will show that circuits are dual to timelike geodesics in the bulk, and that the complexity metric admits a simple bulk geometric description in terms of distances between geodesics. In either case, these quantities are governed by the geometry of coadjoint orbits, which are special symplectic manifolds arising from group theory. The state-changing modular Berry transport process naturally describes the geometry of new, Virasoro-like coadjoint orbits that extend beyond the current classification. The complexity metric describes the geometry of a particular coadjoint orbit of the conformal group in arbitrary dimensions.
I will describe two new quantum information theoretic probes of bulk geometry that access information inaccessible to spacelike geodesics. The first arises from considering a parallel transport process of modular Hamiltonians on the boundary under a change of state. I will show that the Berry curvature for this process computes the entanglement wedge symplectic form associated to a family of Euclidean cosmic brane solutions. Next, I will derive the circuit complexity for conformal field theory in arbitrary dimensions. I will show that circuits are dual to timelike geodesics in the bulk, and that the complexity metric admits a simple bulk geometric description in terms of distances between geodesics. In either case, these quantities are governed by the geometry of coadjoint orbits, which are special symplectic manifolds arising from group theory. The state-changing modular Berry transport process naturally describes the geometry of new, Virasoro-like coadjoint orbits that extend beyond the current classification. The complexity metric describes the geometry of a particular coadjoint orbit of the conformal group in arbitrary dimensions.
Posted by: andrea
Thu
4 Nov 2021
Precision Correlators at Large R-Charge
Simeon Hellerman
(Kavli IPMU and Univ. of Tokyo)
Abstract:
t.b.a. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
t.b.a. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Thu
4 Nov 2021
A method to derive classical gravity from scattering amplitudes
Ludovic Plante
Abstract:
TBA
TBA
Posted by: QMW
Wed
3 Nov 2021
AdS Bulk Locality from Sharp CFT Bounds
๐ London
Dalimil Mazac
(IAS)
Abstract:
It has been a long-standing conjecture that any CFT with a large central charge and a large gap M in the spectrum of single-trace operators must be dual to a local effective field theory in AdS. In my talk, I will discuss a proof of a sharp form of this conjecture. In particular, I will explain how to derive numerical bounds on bulk Wilson coefficients in terms of M using the conformal bootstrap. The bounds exhibit scaling in M expected from dimensional analysis in the bulk. The main technical tools are dispersive CFT sum rules. These sum rules provide a dictionary between CFT dispersion relations and S-matrix dispersion relations in appropriate limits. This dictionary allows one to apply recently-developed flat-space methods to construct positive CFT functionals. My talk will be based on https://arxiv.org/pdf/2106.10274.pdf, which is joint work with S. Caron-Huot, L. Rastelli, and D. Simmons-Duffin.
It has been a long-standing conjecture that any CFT with a large central charge and a large gap M in the spectrum of single-trace operators must be dual to a local effective field theory in AdS. In my talk, I will discuss a proof of a sharp form of this conjecture. In particular, I will explain how to derive numerical bounds on bulk Wilson coefficients in terms of M using the conformal bootstrap. The bounds exhibit scaling in M expected from dimensional analysis in the bulk. The main technical tools are dispersive CFT sum rules. These sum rules provide a dictionary between CFT dispersion relations and S-matrix dispersion relations in appropriate limits. This dictionary allows one to apply recently-developed flat-space methods to construct positive CFT functionals. My talk will be based on https://arxiv.org/pdf/2106.10274.pdf, which is joint work with S. Caron-Huot, L. Rastelli, and D. Simmons-Duffin.
Posted by: andrea
Wed
3 Nov 2021
Geometric Engineering and Correspondences
Michele Del Zotto
(Uppsala)
Abstract:
Over the past decade we have witnessed the emergence of a plethora of correspondences between QFTs in various dimensions arising from higher dimensional SCFTs. In this talk I will overview another strategy to produce correspondences building upon geometric engineering techniques. As applications I will touch upon higher DT theory for Calabi-Yau 3-folds, the algebra of G(2) instantons, and generalizations of level/rank dualities.
Over the past decade we have witnessed the emergence of a plethora of correspondences between QFTs in various dimensions arising from higher dimensional SCFTs. In this talk I will overview another strategy to produce correspondences building upon geometric engineering techniques. As applications I will touch upon higher DT theory for Calabi-Yau 3-folds, the algebra of G(2) instantons, and generalizations of level/rank dualities.
Posted by: IC
Tue
2 Nov 2021
A new look at the gravitational entropy formula
๐ London
Jennifer Lin
(Oxford U.)
Abstract:
The Ryu-Takayanagi formula and its generalizations have led to a surprising amount of progress in our understanding of quantum gravity in the last fifteen years, culminating in the recent derivation of the Page curve in toy models of evaporating black holes. However, we still donรขโฌโขt understand why these formulas are true from a canonical point of view. In this talk, I will attempt to make progress on this problem by developing an analogy between gravitational entropy formulas in low-dimensional examples of holography and similar-looking formulas that have appeared in the study of entanglement entropy in emergent gauge theories. This talk will be based on 1807.06575, 2107.11872, and 2107.12634.
The Ryu-Takayanagi formula and its generalizations have led to a surprising amount of progress in our understanding of quantum gravity in the last fifteen years, culminating in the recent derivation of the Page curve in toy models of evaporating black holes. However, we still donรขโฌโขt understand why these formulas are true from a canonical point of view. In this talk, I will attempt to make progress on this problem by developing an analogy between gravitational entropy formulas in low-dimensional examples of holography and similar-looking formulas that have appeared in the study of entanglement entropy in emergent gauge theories. This talk will be based on 1807.06575, 2107.11872, and 2107.12634.
Posted by: andrea
Tue
2 Nov 2021
Spinning Black Holes Made Simple
Alfredo Guevara
(Harvard University)
Abstract:
I will cover some of the most recent developments on classical spinning black holes and their perturbations. The reinterpretation of them in terms of a classical limit of QFT three-point amplitudes, where the black hole is modeled as a massive spinning particle, sheds light on many fundamental properties such as integrability, the Newman-Janis construction, and the so-called classical double copy relating the solution to gauge theory.
I will cover some of the most recent developments on classical spinning black holes and their perturbations. The reinterpretation of them in terms of a classical limit of QFT three-point amplitudes, where the black hole is modeled as a massive spinning particle, sheds light on many fundamental properties such as integrability, the Newman-Janis construction, and the so-called classical double copy relating the solution to gauge theory.
Posted by: IC
Mon
1 Nov 2021
Lonti: CPT symmetry in Quantum Field Theory
Andreas Fring
(City)
Abstract:
Lonti Autumn 2021 Series: Lecture 3. Release of Recorded Lecture. Available at https://youtu.be/zABaRs1Ghmw
CPT-symmetry is a fundamental symmetry of nature that is respected by all physical processes. It consists of a consecutive reversal of time (T), reflection of space at an arbitrary point (Parity P) and a charge conjugation that replaces particles by antiparticles. I briefly discuss the role P T -symmetry plays in quantum mechanics and how it may be utilised for a consistent formulation of non-Hermitian theories. For a relativistic quantum field theory the CPT-theorem provides the general framework for the validity of this symmetry to occur, by stating that the CPT-symmetry is equivalent to a strong reflection and a simultaneous Hermitian conjugation. In this lecture I will prove the theory in the framework of a Lagrangian quantum field theory for spin 0, 1 and spin 1/2 Dirac fields, by first identifying the separate transformation and a subsequent combination. Subsequently these transformations are used to identify the behaviour of various interaction terms under their action. I conclude by commenting on the experimental observations of CP-symmetry violation in the neutral K-meson decay.
Lonti Autumn 2021 Series: Lecture 3. Release of Recorded Lecture. Available at https://youtu.be/zABaRs1Ghmw
CPT-symmetry is a fundamental symmetry of nature that is respected by all physical processes. It consists of a consecutive reversal of time (T), reflection of space at an arbitrary point (Parity P) and a charge conjugation that replaces particles by antiparticles. I briefly discuss the role P T -symmetry plays in quantum mechanics and how it may be utilised for a consistent formulation of non-Hermitian theories. For a relativistic quantum field theory the CPT-theorem provides the general framework for the validity of this symmetry to occur, by stating that the CPT-symmetry is equivalent to a strong reflection and a simultaneous Hermitian conjugation. In this lecture I will prove the theory in the framework of a Lagrangian quantum field theory for spin 0, 1 and spin 1/2 Dirac fields, by first identifying the separate transformation and a subsequent combination. Subsequently these transformations are used to identify the behaviour of various interaction terms under their action. I conclude by commenting on the experimental observations of CP-symmetry violation in the neutral K-meson decay.
Posted by: pethybridge
Mon
1 Nov 2021
Lonti: (Holographic) Fermi surfaces
David Vegh
(QMUL)
Abstract:
Lonti Autumn 2021 Series: Lecture 2. Live Tutorial.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Abstract: In this lecture, we present a few elementary facts about Fermi surfaces, then discuss how to find interesting ``non-Fermi liquids'' via the AdS/CFT correspondence. We study different backgrounds (e.g. AdS, BTZ, and Reissner-Nordstrom), and the wave-equation of probe fields on top of these geometries. We discuss how to compute boundary two-point functions by solving the bulk equations and then explore the results.
Lonti Autumn 2021 Series: Lecture 2. Live Tutorial.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Abstract: In this lecture, we present a few elementary facts about Fermi surfaces, then discuss how to find interesting ``non-Fermi liquids'' via the AdS/CFT correspondence. We study different backgrounds (e.g. AdS, BTZ, and Reissner-Nordstrom), and the wave-equation of probe fields on top of these geometries. We discuss how to compute boundary two-point functions by solving the bulk equations and then explore the results.
Posted by: pethybridge
October 2021
Thu
28 Oct 2021
Quantum algebras and SUSY interfaces in Bethe/gauge correspondence
Mykola Dedushenko
(SUNY, Stony Brook)
Abstract:
I will describe my work with N.Nekrasov on supersymmetric interfaces in gauge theories in the context of the Bethe/gauge correspondence. These interfaces, viewed as operators on the Hilbert space, give linear maps between spaces of SUSY vacua, understood mathematically as generalized cohomology theories of the Higgs branch. A natural class of interfaces are SUSY Janus interfaces for masses, with the corresponding cohomological maps being either the stable envelopes or the chamber R-matrices (both due to Maulik-Okounkov and Aganagic-Okounkov). Thus, such interfaces (and their collisions) can be used to define actions of the spectrum generating algebras (such as Yangians) on the รขโฌลgaugeรขโฌย side of the Bethe/gauge correspondence, i.e., in QFT. Further applications and possible generalizations will be mentioned as well. –––––––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
I will describe my work with N.Nekrasov on supersymmetric interfaces in gauge theories in the context of the Bethe/gauge correspondence. These interfaces, viewed as operators on the Hilbert space, give linear maps between spaces of SUSY vacua, understood mathematically as generalized cohomology theories of the Higgs branch. A natural class of interfaces are SUSY Janus interfaces for masses, with the corresponding cohomological maps being either the stable envelopes or the chamber R-matrices (both due to Maulik-Okounkov and Aganagic-Okounkov). Thus, such interfaces (and their collisions) can be used to define actions of the spectrum generating algebras (such as Yangians) on the รขโฌลgaugeรขโฌย side of the Bethe/gauge correspondence, i.e., in QFT. Further applications and possible generalizations will be mentioned as well. –––––––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
27 Oct 2021
Supersymmetric Yang–Mills theories on the lattice
David Schaich
(Liverpool)
Abstract:
Lattice field theory provides a non-perturbative regularization suitable for strongly interacting systems, which has proven crucial to the study of quantum chromodynamics among many other theories. Lattice investigations of supersymmetric field theories have a long history but often struggle due to the interplay of supersymmetry with the lattice discretization of space-time. I will discuss a way around these difficulties for d-dimensional supersymmetric Yang–Mills theories with at least 2^d supercharges. After informally reviewing some highlights of the lattice formulation, I will survey a selection of results from recent and ongoing numerical studies, including tests of holographic dualities.
Lattice field theory provides a non-perturbative regularization suitable for strongly interacting systems, which has proven crucial to the study of quantum chromodynamics among many other theories. Lattice investigations of supersymmetric field theories have a long history but often struggle due to the interplay of supersymmetry with the lattice discretization of space-time. I will discuss a way around these difficulties for d-dimensional supersymmetric Yang–Mills theories with at least 2^d supercharges. After informally reviewing some highlights of the lattice formulation, I will survey a selection of results from recent and ongoing numerical studies, including tests of holographic dualities.
Posted by: IC
Wed
27 Oct 2021
Analyticity and Unitarity for Cosmological Correlators
๐ London
Shota Komatsu
(CERN)
Abstract:
I will discuss the fundamentals of quantum field theory on a rigid de Sitter space. First, I will show that the perturbative expansion of late-time correlation functions to all orders can be equivalently generated by a non-unitary Lagrangian on a Euclidean AdS geometry. This finding simplifies dramatically perturbative computations, as well as allows us to establish basic properties of these correlators, which comprise a Euclidean CFT. Second, I use this to infer the analytic structure of the spectral density that captures the conformal partial wave expansion of a late-time four-point function, to derive an OPE expansion, and to constrain the operator spectrum. Third, I will prove that unitarity of the de Sitter theory manifests itself as the positivity of the spectral density. This statement does not rely on the use of Euclidean AdS Lagrangians and holds non-perturbatively.
Zoom link: https://us06web.zoom.us/j/82867324531?pwd=cXBkMUNpQlE4M3h2UEdabWpOZkNIdz09
I will discuss the fundamentals of quantum field theory on a rigid de Sitter space. First, I will show that the perturbative expansion of late-time correlation functions to all orders can be equivalently generated by a non-unitary Lagrangian on a Euclidean AdS geometry. This finding simplifies dramatically perturbative computations, as well as allows us to establish basic properties of these correlators, which comprise a Euclidean CFT. Second, I use this to infer the analytic structure of the spectral density that captures the conformal partial wave expansion of a late-time four-point function, to derive an OPE expansion, and to constrain the operator spectrum. Third, I will prove that unitarity of the de Sitter theory manifests itself as the positivity of the spectral density. This statement does not rely on the use of Euclidean AdS Lagrangians and holds non-perturbatively.
Zoom link: https://us06web.zoom.us/j/82867324531?pwd=cXBkMUNpQlE4M3h2UEdabWpOZkNIdz09
Posted by: oxford
Wed
27 Oct 2021
Comments on Large Charge and Holography
๐ London
Shota Komatsu
(CERN)
Abstract:
I will discuss two topics on the large charge limit and holography. First, I will discuss general features of the large-charge limit of superconformal field theories at large N. In particular, I will point out a simple setup to analyze the large charge expansion of the planar N=4 super Yang-Mills and discuss its holographic interpretation. Second, I will discuss the large-charge limit of the defect CFT on the Wilson line and its relation to the matrix model.
Zoom link: https://us06web.zoom.us/j/82867324531?pwd=cXBkMUNpQlE4M3h2UEdabWpOZkNIdz09
I will discuss two topics on the large charge limit and holography. First, I will discuss general features of the large-charge limit of superconformal field theories at large N. In particular, I will point out a simple setup to analyze the large charge expansion of the planar N=4 super Yang-Mills and discuss its holographic interpretation. Second, I will discuss the large-charge limit of the defect CFT on the Wilson line and its relation to the matrix model.
Zoom link: https://us06web.zoom.us/j/82867324531?pwd=cXBkMUNpQlE4M3h2UEdabWpOZkNIdz09
Posted by: oxford
Tue
26 Oct 2021
Black hole microstates from the worldsheet
David Turton
(Southampton)
Abstract:
I will describe recent studies of bound states of NS5 branes carrying momentum and/or fundamental string charge, in the decoupling limits leading to little string theory and to AdS3/CFT2 duality. This work involves a class of exactly solvable worldsheet models that describe families of BPS and non-BPS black hole microstates. These models have enabled studies of string and D-brane probes of these microstates, yielding insight into their stringy structure in the gravitational bulk description.
I will describe recent studies of bound states of NS5 branes carrying momentum and/or fundamental string charge, in the decoupling limits leading to little string theory and to AdS3/CFT2 duality. This work involves a class of exactly solvable worldsheet models that describe families of BPS and non-BPS black hole microstates. These models have enabled studies of string and D-brane probes of these microstates, yielding insight into their stringy structure in the gravitational bulk description.
Posted by: IC
Tue
26 Oct 2021
In Conversation with Sir Roger Penrose
Roger Penrose
(Oxford)
Abstract:
In conversation:
Sir Roger Penrose, Thomas Fink & Yang-Hui He
Live at the Royal Institution + Livestream
Sir Roger Penrose is a mathematical physicist with the eye of an artist and the soul of a philosopher. He won the 2020 Nobel Prize in Physics for his work on the mathematical foundations of black holes. The tilings which bear his name can cover the plane in a never-repeating pattern. His work on the theory of mind suggests consciousness is a peculiarly human capability. He is a master word-smither, capable of rendering the most complex ideas clear, and his popular books have inspired a generation of physicists and laymen alike.
In this event, Sir Roger joins Thomas Fink and Yang-Hui He on stage for a conversation about the man behind the science. We take a rare look into the workings of this singular mind. How does he get his ideas? Is beauty a guide to truth? Whatรขโฌโขs the basis of free will? Is AI a threat? Can art inform science? And is man different from machine?
https://www.rigb.org/whats-on/events-2021/october/public-in-conversation-with-sir-roger-penrose
https://lims.ac.uk/event/in-conversation-with-sir-roger-penrose/
In conversation:
Sir Roger Penrose, Thomas Fink & Yang-Hui He
Live at the Royal Institution + Livestream
Sir Roger Penrose is a mathematical physicist with the eye of an artist and the soul of a philosopher. He won the 2020 Nobel Prize in Physics for his work on the mathematical foundations of black holes. The tilings which bear his name can cover the plane in a never-repeating pattern. His work on the theory of mind suggests consciousness is a peculiarly human capability. He is a master word-smither, capable of rendering the most complex ideas clear, and his popular books have inspired a generation of physicists and laymen alike.
In this event, Sir Roger joins Thomas Fink and Yang-Hui He on stage for a conversation about the man behind the science. We take a rare look into the workings of this singular mind. How does he get his ideas? Is beauty a guide to truth? Whatรขโฌโขs the basis of free will? Is AI a threat? Can art inform science? And is man different from machine?
https://www.rigb.org/whats-on/events-2021/october/public-in-conversation-with-sir-roger-penrose
https://lims.ac.uk/event/in-conversation-with-sir-roger-penrose/
Posted by: oxford
Mon
25 Oct 2021
Lonti: What is an Anomaly?
๐ London
Chris Herzog
(KCL)
Abstract:
Lonti Autumn 2021 Series: Lecture 1. Live Tutorial.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Four examples of an anomaly are presented, two from quantum mechanics and two from quantum field theory. The first example is a charged bead on a wire in the presence of a magnetic field. This example of a 't Hooft anomaly is related to the theta angle in Yang-Mills theory. The remaining three examples present scale and conformal anomalies. We will scatter a plane wave off an attractive delta function in two dimensions. We also look at a massless scalar field, both in two dimensions without a boundary and in three dimensions with one.
Lonti Autumn 2021 Series: Lecture 1. Live Tutorial.
Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
Four examples of an anomaly are presented, two from quantum mechanics and two from quantum field theory. The first example is a charged bead on a wire in the presence of a magnetic field. This example of a 't Hooft anomaly is related to the theta angle in Yang-Mills theory. The remaining three examples present scale and conformal anomalies. We will scatter a plane wave off an attractive delta function in two dimensions. We also look at a massless scalar field, both in two dimensions without a boundary and in three dimensions with one.
Posted by: pethybridge
Mon
25 Oct 2021
Lonti: (Holographic) Fermi Surfaces
David Vegh
(QMUL)
Abstract:
Lonti Autumn 2021 Series: Lecture 2. Release of Recorded Lecture. Available at https://youtu.be/5IAx2ca_WU4
Abstract: In this lecture, we present a few elementary facts about Fermi surfaces, then discuss how to find interesting "non-Fermi liquids" via the AdS/CFT correspondence. We study different backgrounds (e.g. AdS, BTZ, and Reissner-Nordstrom), and the wave-equation of probe fields on top of these geometries. We discuss how to compute boundary two-point functions by solving the bulk equations and then explore the results.
Lonti Autumn 2021 Series: Lecture 2. Release of Recorded Lecture. Available at https://youtu.be/5IAx2ca_WU4
Abstract: In this lecture, we present a few elementary facts about Fermi surfaces, then discuss how to find interesting "non-Fermi liquids" via the AdS/CFT correspondence. We study different backgrounds (e.g. AdS, BTZ, and Reissner-Nordstrom), and the wave-equation of probe fields on top of these geometries. We discuss how to compute boundary two-point functions by solving the bulk equations and then explore the results.
Posted by: pethybridge
Thu
21 Oct 2021
The Principles of Deep Learning Theory
Dan Roberts
(MIT)
Abstract:
[for zoom link please email s.nagy@qmul.ac.uk]
Deep learning is an exciting approach to modern artificial intelligence based on artificial neural networks. The goal of this talk is to provide a blueprint รขโฌโ using tools from physics รขโฌโ for theoretically analyzing deep neural networks of practical relevance. This task will encompass both understanding the statistics of initialized deep networks and determining the training dynamics of such an ensemble when learning from data.
In terms of their "microscopic" definition, deep neural networks are a flexible set of functions built out of many basic computational blocks called neurons, with many neurons in parallel organized into sequential layers. Borrowing from the effective theory framework, we will develop a perturbative 1/n expansion around the limit of an infinite number of neurons per layer and systematically integrate out the parameters of the network. We will explain how the network simplifies at large width and how the propagation of signals from layer to layer can be understood in terms of a Wilsonian renormalization group flow. This will make manifest that deep networks have a tuning problem, analogous to criticality, that needs to be solved in order to make them useful. Ultimately we will find a "macroscopic" description for wide and deep networks in terms of weakly-interacting statistical models, with the strength of the interactions between the neurons growing with depth-to-width aspect ratio of the network. Time permitting, we will explain how the interactions induce representation learning.
This talk is based on a book, "The Principles of Deep Learning Theory," co-authored with Sho Yaida and based on research also in collaboration with Boris Hanin. It will be published next year by Cambridge University Press.
[for zoom link please email s.nagy@qmul.ac.uk]
Deep learning is an exciting approach to modern artificial intelligence based on artificial neural networks. The goal of this talk is to provide a blueprint รขโฌโ using tools from physics รขโฌโ for theoretically analyzing deep neural networks of practical relevance. This task will encompass both understanding the statistics of initialized deep networks and determining the training dynamics of such an ensemble when learning from data.
In terms of their "microscopic" definition, deep neural networks are a flexible set of functions built out of many basic computational blocks called neurons, with many neurons in parallel organized into sequential layers. Borrowing from the effective theory framework, we will develop a perturbative 1/n expansion around the limit of an infinite number of neurons per layer and systematically integrate out the parameters of the network. We will explain how the network simplifies at large width and how the propagation of signals from layer to layer can be understood in terms of a Wilsonian renormalization group flow. This will make manifest that deep networks have a tuning problem, analogous to criticality, that needs to be solved in order to make them useful. Ultimately we will find a "macroscopic" description for wide and deep networks in terms of weakly-interacting statistical models, with the strength of the interactions between the neurons growing with depth-to-width aspect ratio of the network. Time permitting, we will explain how the interactions induce representation learning.
This talk is based on a book, "The Principles of Deep Learning Theory," co-authored with Sho Yaida and based on research also in collaboration with Boris Hanin. It will be published next year by Cambridge University Press.
Posted by: QMW
Thu
21 Oct 2021
Matrix bootstrap revisited
Zechuan Zheng
(ENS Paris)
Abstract:
Matrix bootstrap is a new method for the numerical study of (multi)-matrix models in the planar limit, using loop equations for moments of distribution (Ward identities and factorization of traces at infinite N). The lack of information associated with the use of only a finite number of lower moments is supplemented by the conditions of positivity of the correlation matrix. The numerical solution of loop equations and these conditions leads to inequalities for the lowest moments, which rapidly converge to exact values with an increase in the number of used moments. In our work https://arxiv.org/pdf/2108.04830.pdf, the method was tested on the example of the standard one-matrix model, as well as on the case of an ''unsolvable'' 2-matrix model with the interaction tr[A, B]^2 and with quartic potentials. We propose a significant improvement of original H. Lin's proposal for matrix bootstrap by introducing the relaxation procedure: we replace the non-convex, non-linear loop equations by convex inequalities. The results look quite convincing and matrix bootstrap seems to be an interesting alternative to the Monte Carlo method. For example, for < tr A^2 >, the precision reaches 6 digits (with modest computer resources). I will discuss the prospects for applying the method in other, physically interesting systems. ––––––––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Matrix bootstrap is a new method for the numerical study of (multi)-matrix models in the planar limit, using loop equations for moments of distribution (Ward identities and factorization of traces at infinite N). The lack of information associated with the use of only a finite number of lower moments is supplemented by the conditions of positivity of the correlation matrix. The numerical solution of loop equations and these conditions leads to inequalities for the lowest moments, which rapidly converge to exact values with an increase in the number of used moments. In our work https://arxiv.org/pdf/2108.04830.pdf, the method was tested on the example of the standard one-matrix model, as well as on the case of an ''unsolvable'' 2-matrix model with the interaction tr[A, B]^2 and with quartic potentials. We propose a significant improvement of original H. Lin's proposal for matrix bootstrap by introducing the relaxation procedure: we replace the non-convex, non-linear loop equations by convex inequalities. The results look quite convincing and matrix bootstrap seems to be an interesting alternative to the Monte Carlo method. For example, for < tr A^2 >, the precision reaches 6 digits (with modest computer resources). I will discuss the prospects for applying the method in other, physically interesting systems. ––––––––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
20 Oct 2021
Renormalization Group Flows on Line Defects
๐ London
Avia Raviv-Moshe
(Stony Brook U., New York, SCGP)
Abstract:
In this talk, we will consider line defects in d-dimensional CFTs. The ambient CFT places nontrivial constraints on renormalization group flows on such line defects. We will see that the flow on line defects is consequently irreversible and furthermore a canonical decreasing entropy function exists. This construction generalizes the g theorem to line defects in arbitrary dimensions. We will demonstrate this generalization in some concrete examples, including a flow between Wilson loops in 4 dimensions, and an O(3) bosonic theory coupled to impurities with large isospin.
In this talk, we will consider line defects in d-dimensional CFTs. The ambient CFT places nontrivial constraints on renormalization group flows on such line defects. We will see that the flow on line defects is consequently irreversible and furthermore a canonical decreasing entropy function exists. This construction generalizes the g theorem to line defects in arbitrary dimensions. We will demonstrate this generalization in some concrete examples, including a flow between Wilson loops in 4 dimensions, and an O(3) bosonic theory coupled to impurities with large isospin.
Posted by: andrea
Tue
19 Oct 2021
New postdoc introduction
David Tennyson and Morteza Hosseini
(Imperial)
Abstract:
Morteza Hosseini: "Microstates of AdS black holes in string theory." Iรขโฌโขll review recent advances of counting black holes microstates in AdS spacetimes.
David Tennyson: "Supersymmetric flux backgrounds of string theory." I will review my work on the geometry of supersymmetric flux backgrounds of string theory through generalised geometry. In particular, I will introduce the exceptional complex structure and discuss some applications.
Morteza Hosseini: "Microstates of AdS black holes in string theory." Iรขโฌโขll review recent advances of counting black holes microstates in AdS spacetimes.
David Tennyson: "Supersymmetric flux backgrounds of string theory." I will review my work on the geometry of supersymmetric flux backgrounds of string theory through generalised geometry. In particular, I will introduce the exceptional complex structure and discuss some applications.
Posted by: IC
Mon
18 Oct 2021
Lonti: What is an Anomaly?
๐ London
Chris Herzog
(KCL)
Abstract:
Lonti Autumn 2021 Series: Lecture 1. Release of Recorded Lecture. Available here:
https://youtu.be/hiUnq_5iiPM.
Four examples of an anomaly are presented, two from quantum mechanics and two from quantum field theory. The first example is a charged bead on a wire in the presence of a magnetic field. This example of a 't Hooft anomaly is related to the theta angle in Yang-Mills theory. The remaining three examples present scale and conformal anomalies. We will scatter a plane wave off an attractive delta function in two dimensions. We also look at a massless scalar field, both in two dimensions without a boundary and in three dimensions with one.
Lonti Autumn 2021 Series: Lecture 1. Release of Recorded Lecture. Available here:
https://youtu.be/hiUnq_5iiPM.
Four examples of an anomaly are presented, two from quantum mechanics and two from quantum field theory. The first example is a charged bead on a wire in the presence of a magnetic field. This example of a 't Hooft anomaly is related to the theta angle in Yang-Mills theory. The remaining three examples present scale and conformal anomalies. We will scatter a plane wave off an attractive delta function in two dimensions. We also look at a massless scalar field, both in two dimensions without a boundary and in three dimensions with one.
Posted by: pethybridge
Thu
14 Oct 2021
Lessons and surprises from Kaluza-Klein spectra
Gabriel Larios
(UAM)
Abstract:
[foor zoom link please email s.nagy@qmul.ac.uk]
Infinite towers of massive modes arise for every compactification of higher dimensional theories. Understanding the properties of these Kaluza-Klein towers on non-trivial solutions with an AdS factor has been a longstanding issue with clear holographic interest, as they describe the spectrum of single-trace operators of the dual CFTs at strong coupling and large N. In this talk, I will focus on two classes of solutions of such kind. The first class consists of AdS4 solutions of D=11 and Type II supergravity that can be obtained from maximal gauged supergravities in D=4. For the later part, I will describe new families of solutions in N=(1,1) supergravity in D=6 which uplift from half-maximal supergravity in D=3. In both cases, the spectra can be computed using recent techniques from Exceptional Field Theory, and the information thus obtained leads to several unexpected conclusions.
[foor zoom link please email s.nagy@qmul.ac.uk]
Infinite towers of massive modes arise for every compactification of higher dimensional theories. Understanding the properties of these Kaluza-Klein towers on non-trivial solutions with an AdS factor has been a longstanding issue with clear holographic interest, as they describe the spectrum of single-trace operators of the dual CFTs at strong coupling and large N. In this talk, I will focus on two classes of solutions of such kind. The first class consists of AdS4 solutions of D=11 and Type II supergravity that can be obtained from maximal gauged supergravities in D=4. For the later part, I will describe new families of solutions in N=(1,1) supergravity in D=6 which uplift from half-maximal supergravity in D=3. In both cases, the spectra can be computed using recent techniques from Exceptional Field Theory, and the information thus obtained leads to several unexpected conclusions.
Posted by: QMW
Thu
14 Oct 2021
Dynamical spin chains in 4D N = 2 SCFTs
Elli Pomoni
(DESY)
Abstract:
In this talk we will revisit the study of spin chains capturing the spectral problem of 4d N = 2 SCFTs in the planar limit. At one loop and in the quantum plane limit, we will discover a quasi-Hopf symmetry algebra, defined by the R-matrix read off from the superpotential. This implies that when orbifolding the N = 4 symmetry algebra down to the N = 2 one and then marginaly deforming, the broken generators are not lost, but get upgraded to quantum generators. We will also demonstrate that these chains are dynamical, in the sense that their Hamiltonian depends on a parameter which is dynamically determined along the chain. At one loop we will show how to map the holomorphic SU(3) scalar sector to a dynamical 15-vertex model, which corresponds to an RSOS model, whose adjacency graph can be read off from the gauge theory quiver/brane tiling. One scalar SU(2) sub-sector is described by an alternating nearest-neighbour Hamiltonian, while another choice of SU(2) sub-sector leads to a dynamical dilute Temperley-Lieb model. These sectors have a common vacuum state, around which the magnon dispersion relations are naturally uniformised by elliptic functions. For the example of the รขโยค_{2} quiver theory we study these dynamical chains by solving the one- and two-magnon problems with the coordinate Bethe ansatz approach. –- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed on Tuesday.
In this talk we will revisit the study of spin chains capturing the spectral problem of 4d N = 2 SCFTs in the planar limit. At one loop and in the quantum plane limit, we will discover a quasi-Hopf symmetry algebra, defined by the R-matrix read off from the superpotential. This implies that when orbifolding the N = 4 symmetry algebra down to the N = 2 one and then marginaly deforming, the broken generators are not lost, but get upgraded to quantum generators. We will also demonstrate that these chains are dynamical, in the sense that their Hamiltonian depends on a parameter which is dynamically determined along the chain. At one loop we will show how to map the holomorphic SU(3) scalar sector to a dynamical 15-vertex model, which corresponds to an RSOS model, whose adjacency graph can be read off from the gauge theory quiver/brane tiling. One scalar SU(2) sub-sector is described by an alternating nearest-neighbour Hamiltonian, while another choice of SU(2) sub-sector leads to a dynamical dilute Temperley-Lieb model. These sectors have a common vacuum state, around which the magnon dispersion relations are naturally uniformised by elliptic functions. For the example of the รขโยค_{2} quiver theory we study these dynamical chains by solving the one- and two-magnon problems with the coordinate Bethe ansatz approach. –- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed on Tuesday.
Posted by: andrea
Wed
13 Oct 2021
Separation of variables and correlation functions in high-rank integrable systems
๐ London
Paul Ryan
(KCL / Trinity College Dublin)
Abstract:
The spectral problem for N=4 Super Yang-Mills can be formulated as a set of quantisation conditions on a handful of functions called Q-functions. Recent analysis suggests that the Q-functions can be used as simple building blocks for 3-point correlation functions. This strongly resembles the situation in integrable spin chains where the wave functions factorise into a simple product of Q-functions in a special basis called Sklyaninรขโฌโขs separation of variables (SoV) basis which is one of the most powerful approaches for solving integrable systems. Unfortunately this framework has only been developed for the simplest integrable spin chains with sl(2) symmetry, far from the psu(2,2|4) needed to describe N=4 SYM. In this talk I will review recent advances in developing the SoV approach for higher rank integrable spin chains. I will explain how to construct the SoV basis in a systematic fashion and how it links to the representation theory of the system. Next, I will discuss a new approach for obtaining the measure in separated variables based on the famous Baxter TQ equation and how the approach naturally provides a large family of correlation functions as very simple determinants in Q-functions. I will briefly discuss how the approach can be applied directly to certain 4d QFTs, in particular the fishnet cousin of N=4 SYM.
The spectral problem for N=4 Super Yang-Mills can be formulated as a set of quantisation conditions on a handful of functions called Q-functions. Recent analysis suggests that the Q-functions can be used as simple building blocks for 3-point correlation functions. This strongly resembles the situation in integrable spin chains where the wave functions factorise into a simple product of Q-functions in a special basis called Sklyaninรขโฌโขs separation of variables (SoV) basis which is one of the most powerful approaches for solving integrable systems. Unfortunately this framework has only been developed for the simplest integrable spin chains with sl(2) symmetry, far from the psu(2,2|4) needed to describe N=4 SYM. In this talk I will review recent advances in developing the SoV approach for higher rank integrable spin chains. I will explain how to construct the SoV basis in a systematic fashion and how it links to the representation theory of the system. Next, I will discuss a new approach for obtaining the measure in separated variables based on the famous Baxter TQ equation and how the approach naturally provides a large family of correlation functions as very simple determinants in Q-functions. I will briefly discuss how the approach can be applied directly to certain 4d QFTs, in particular the fishnet cousin of N=4 SYM.
Posted by: andrea
Tue
12 Oct 2021
Quantum algebras in supersymmetric gauge theories: interfaces and stable envelopes
Nikita Nekrasov
(SCGP, Stony Brook and Center for Advanced Studies, Skoltech, Moscow)
Abstract:
I will give an overview of a three decade long project of novel symmetries in quantum field theory, with the emphasis on the most recent development concerning the realisation of stable envelopes (proposed by A. Okounkov and collaborators) and R-matrices via supersymmetric interfaces in 1-2-3 dimensional supersymmetric gauge theories. Based on the recent paper arXiv:2109.10941 with Mykola Dedushenko.
I will give an overview of a three decade long project of novel symmetries in quantum field theory, with the emphasis on the most recent development concerning the realisation of stable envelopes (proposed by A. Okounkov and collaborators) and R-matrices via supersymmetric interfaces in 1-2-3 dimensional supersymmetric gauge theories. Based on the recent paper arXiv:2109.10941 with Mykola Dedushenko.
Posted by: IC
Thu
7 Oct 2021
The Gravitino and the Swampland
Dieter Lust
(Munich)
Abstract:
[for zoom details please email s.nagy@qmul.ac.uk]
In this talk we discuss a new swampland conjecture stating that the limit of vanishing gravitino mass corresponds to the massless limit of an infinite tower of states and to the consequent breakdown of the effective field theory. The proposal can be tested in large classes of models coming from compactification of string theory to four dimensions, where we identify the Kaluza-Klein nature of the tower of states becoming light. We point out a general relation between the gravitino mass and an abelian gauge coupling, which allows us to connect our conjecture to the weak gravity conjecture or the absence of global symmetries in quantum gravity. We discuss phenomenological implications of our conjecture in (quasi-)de Sitter backgrounds and extract a lower bound for the gravitino mass in terms of the Hubble parameter.
[for zoom details please email s.nagy@qmul.ac.uk]
In this talk we discuss a new swampland conjecture stating that the limit of vanishing gravitino mass corresponds to the massless limit of an infinite tower of states and to the consequent breakdown of the effective field theory. The proposal can be tested in large classes of models coming from compactification of string theory to four dimensions, where we identify the Kaluza-Klein nature of the tower of states becoming light. We point out a general relation between the gravitino mass and an abelian gauge coupling, which allows us to connect our conjecture to the weak gravity conjecture or the absence of global symmetries in quantum gravity. We discuss phenomenological implications of our conjecture in (quasi-)de Sitter backgrounds and extract a lower bound for the gravitino mass in terms of the Hubble parameter.
Posted by: QMW
Thu
7 Oct 2021
Renormalization Group Flows on Line Defects
Zohar Komargodski
(Simons Center)
Abstract:
We will review the subject of line defects in d-dimensional Conformal Field Theories (CFTs). We discuss an exact formula governing the renormalization group flow on line defects and consider some examples involving line defects in 2,3, and 4 space-time dimensions.
–––––––– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
We will review the subject of line defects in d-dimensional Conformal Field Theories (CFTs). We discuss an exact formula governing the renormalization group flow on line defects and consider some examples involving line defects in 2,3, and 4 space-time dimensions.
–––––––– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
6 Oct 2021
Instantons, symmetries and anomalies in five dimensions
๐ London
Pietro Benetti Genolini
(KCL / Cambridge Univ. DAMTP)
Abstract:
Five-dimensional non-abelian gauge theories have a U(1) global symmetry associated with instantonic particles. I will describe a mixed 't Hooft anomaly between this and other global symmetries of the theory, namely the one-form center symmetry or ordinary flavor symmetry for theories with fundamental matter. I will then apply these results to supersymmetric gauge theories, analysing the symmetry enhancement patterns occurring at their conjectured RG fixed points.
Five-dimensional non-abelian gauge theories have a U(1) global symmetry associated with instantonic particles. I will describe a mixed 't Hooft anomaly between this and other global symmetries of the theory, namely the one-form center symmetry or ordinary flavor symmetry for theories with fundamental matter. I will then apply these results to supersymmetric gauge theories, analysing the symmetry enhancement patterns occurring at their conjectured RG fixed points.
Posted by: andrea
Wed
6 Oct 2021
Constructing the 6 Loop 4 Point N=4 super-Yang-Mills Integrand
Alex Edison
(Uppsala U.)
Abstract:
In this talk, we'll discuss the current state-of-the-art for constructing multi-loop integrands in N=4 super-Yang-Mills. After briefly covering some of the key goals, background, and ideas behind the multiloop integrand program, we turn to the cutting edge: constructing the complete (planar and non-planar) integrand for the six-loop four-point amplitude in maximal \(D\le10\) super-Yang-Mills. This construction employs new advances that combat the proliferation of loops and state-sums when evaluating multi-loop \(D\)-dimensional unitarity cuts. Concretely, it uses two graph-based approaches, applicable in a range of theories, to evaluating generalized unitarity cuts in \(D\) dimensions: 1) recursively from lower-loop cuts, or 2) directly from known higher-loop planar cuts. Neither method relies on explicit state sums or any sewing of tree-level amplitudes. The first method meshes particularly well with the Method of Maximal Cuts to allow direct construction of the complete six-loop integrand.
In this talk, we'll discuss the current state-of-the-art for constructing multi-loop integrands in N=4 super-Yang-Mills. After briefly covering some of the key goals, background, and ideas behind the multiloop integrand program, we turn to the cutting edge: constructing the complete (planar and non-planar) integrand for the six-loop four-point amplitude in maximal \(D\le10\) super-Yang-Mills. This construction employs new advances that combat the proliferation of loops and state-sums when evaluating multi-loop \(D\)-dimensional unitarity cuts. Concretely, it uses two graph-based approaches, applicable in a range of theories, to evaluating generalized unitarity cuts in \(D\) dimensions: 1) recursively from lower-loop cuts, or 2) directly from known higher-loop planar cuts. Neither method relies on explicit state sums or any sewing of tree-level amplitudes. The first method meshes particularly well with the Method of Maximal Cuts to allow direct construction of the complete six-loop integrand.
Posted by: QMW
Tue
5 Oct 2021
Aspects of the black hole/string transition
Yiming Chen
(Princeton University)
Abstract:
Abstract: It has long been speculated that a black hole in string theory turns into highly excited strings close to the Hagedorn temperature. Gravitational attraction pulls different parts of the string together, forming a star-like configuration. In this talk, I will review the properties of a concrete solution of this kind, first discovered by Horowitz and Polchinski. I will discuss whether the Horowitz-Polchinski solution can be smoothly connected with the black hole as worldsheet CFTs. I will also discuss how the story can be generalized to charged cases, as well as its implication on the near extremal limit.
Abstract: It has long been speculated that a black hole in string theory turns into highly excited strings close to the Hagedorn temperature. Gravitational attraction pulls different parts of the string together, forming a star-like configuration. In this talk, I will review the properties of a concrete solution of this kind, first discovered by Horowitz and Polchinski. I will discuss whether the Horowitz-Polchinski solution can be smoothly connected with the black hole as worldsheet CFTs. I will also discuss how the story can be generalized to charged cases, as well as its implication on the near extremal limit.
Posted by: IC
September 2021
Wed
29 Sep 2021
In search of fixed points in non-abelian gauge theories using perturbation theory
๐ London
Marco Serone
(SISSA, INFN Trieste)
Abstract:
Four-dimensional gauge theories can flow in the IR to non-trivial CFTs.
By employing Borel resummation techniques both to the ordinary perturbative series and to the Banks-Zaks conformal expansion, we first analyze the conformal window of QCD and find substantial evidence that QCD with n_f=12 flavours flows in the IR to a CFT.
We then study UV fixed points for SU(n_c) gauge theories with fundamental fermion matter in 4+2epsilon dimensions. Using resummation techniques similar to those used in the 4d QCD case, we provide evidence for the existence of non-supersymmetric CFTs in d=5 space-time dimensions in a certain range of colors and flavours.
Four-dimensional gauge theories can flow in the IR to non-trivial CFTs.
By employing Borel resummation techniques both to the ordinary perturbative series and to the Banks-Zaks conformal expansion, we first analyze the conformal window of QCD and find substantial evidence that QCD with n_f=12 flavours flows in the IR to a CFT.
We then study UV fixed points for SU(n_c) gauge theories with fundamental fermion matter in 4+2epsilon dimensions. Using resummation techniques similar to those used in the 4d QCD case, we provide evidence for the existence of non-supersymmetric CFTs in d=5 space-time dimensions in a certain range of colors and flavours.
Posted by: andrea
Wed
22 Sep 2021
The volume of the black hole interior at late times
๐ London
Luca Iliesiu
(Stanford U.)
Abstract:
Understanding the fate of semi-classical black hole solutions at very late times is one of the most important open questions in quantum gravity. In this paper, we provide a path integral definition of the volume of the black hole interior and study it at arbitrarily late times for black holes in various models of two-dimensional gravity. Because of a novel universal cancellation between the contributions of the semi-classical black hole spectrum and some of its non-perturbative corrections, we find that, after a linear growth at early times, the length of the interior saturates at a time, and towards a value, that is exponentially large in the entropy of the black hole. This provides a non-perturbative confirmation of the complexity equals volume proposal since complexity is also expected to plateau at the same value and at the same time.
Understanding the fate of semi-classical black hole solutions at very late times is one of the most important open questions in quantum gravity. In this paper, we provide a path integral definition of the volume of the black hole interior and study it at arbitrarily late times for black holes in various models of two-dimensional gravity. Because of a novel universal cancellation between the contributions of the semi-classical black hole spectrum and some of its non-perturbative corrections, we find that, after a linear growth at early times, the length of the interior saturates at a time, and towards a value, that is exponentially large in the entropy of the black hole. This provides a non-perturbative confirmation of the complexity equals volume proposal since complexity is also expected to plateau at the same value and at the same time.
Posted by: andrea
Mon
13 Sep 2021
Towards a mathematical definition of the 3d superconformal index
๐ London
Mathew Bullimore
(Durham University)
Abstract:
The aim of this talk is to give a mathematical definition of the superconformal index of 3d supersymmetric gauge theories. This can be computed exactly using supersymmetric localisation, leading to an explicit contour integral formula involving infinite q-Pochammer symbols. I will explain how this may be understood as the Witten index of a supersymmetric quantum mechanics, or index of a twisted Dirac operator on a certain infinite-dimensional space closely related to one introduced by Braverman-Finkelberg-Nakajima.
The aim of this talk is to give a mathematical definition of the superconformal index of 3d supersymmetric gauge theories. This can be computed exactly using supersymmetric localisation, leading to an explicit contour integral formula involving infinite q-Pochammer symbols. I will explain how this may be understood as the Witten index of a supersymmetric quantum mechanics, or index of a twisted Dirac operator on a certain infinite-dimensional space closely related to one introduced by Braverman-Finkelberg-Nakajima.
Posted by: andrea