Speaker: M. M. Sheikh-Jabbari (IPM)
Date & Time: 16:30-17:30, Thu Jun 30
Title: Gravity ⇋ Thermodynamics
Abstract: Last 50 years' developments have revealed deep relations between thermodynamics and gravity as formulated in Einstein general relativity, despite their apparent differences. These relations seem so fundamental and deep that they have prompted the idea that they may be telling us about the very nature of gravity. In this talk I review these salient features and discuss recent developments in the connection between gravity and thermodynamics. In particular, I describe how general covariance ingravity theories leads to laws of thermodynamics when we consider gravity on spacetimes with null boundaries.
Recording: Link to video Password: 9*4EU%vW
Speaker: Cumrun Vafa (Harvard University)
Date & Time: 9:00-10:00, Thu Jun 23
Title: Geometric Obstruction to Scale Separation
Abstract: In this talk I review the obstructions to scale separation for quantum gravitational backgrounds involving AdS space. This basically means that the overall aspects of the internal geometry are deeply linked with the curvature of the macroscopic AdS space it gives rise to. These obstructions include evidence of a no-go conjecture in the context of Einstein manifolds which puts a lower bound on its diameter, as well as explaining geometric issues arising in the KKLT scenario which prevents it from giving rise to a counter-example.
Recording: Link to video Password: 77QN=K3N
Speaker: Wei Song (Tsinghua University)
Date & Time: 16:30-17:30, Thu Jun 16
Title: TTbar and holography
Abstract: (The double trace version of) TTbar deformation is a solvable irrelevant deformation of conformal field theories, the spectrum of which is determined by the undeformed theory and the deformation parameter. It has been proposed that for one particular choice of the sign of the deformation parameter, TTbar deformation is holographical dual to AdS$3$ gravity with a finite cutoff. In this talk, I will describe a proposal of the holographic dual to (the double-trace) TTbar deformation with the other choice of the sign of the deformation parameter.
By applying the TTbar deformation to the seed theory of a symmetric product CFT, we can construct the so-called single trace version of TTbar deformation, which can be used to build a toy model of holographic duality beyond AdS/CFT in string theory, with the bulk metric interpolating BTZ black holes in the IR and linear dilaton background in the UV. We will show that this new string background can be obtained by TsT transformations( T-duality, shift, and T-duality). As supporting evidence, we find a matching of the deformed spectrum, the thermodynamics, and a critical value of the deformation parameter. Similarly, TsT transformations can also be used to generate the holographic dual for the single trace version of JTbar, and TTbar+JTbar+TJbar deformations.
Slides: Link to slides Recording: Link to video Password: Xj.2fTb$
Speaker: Kostas Skenderis (University of Southampton)
Date & Time: 16:30-17:30, Thu Jun 9
Title: Fluxes and charges in de Sitter
Abstract: The proper definition of conserved charges in gravitational theories is a notoriously difficult problem. Diffeomorphism invariance implies that non-trivial charges may only be defined as surface integrals at infinity but due to the infinite volume of spacetime any such definition requires a subtraction, potentially making the charges ambiguous. In this talk I will discuss the definition of conserved charges in asymptotically locally de Sitter spacetimes. De Sitter spacetimes have additional subtleties: there are no global timelike Killing vectors even for exact de Sitter and there is also no spacelike infinity; rather the asymptotic regions are in the time direction. We use methodology inspire from holography and the formalism of covariant phase space to discuss the construction of charges, discuss quantities which are conserved under time evolution in the absence of gravitational flux but otherwise change according to the amount of the net gravitational flux entering or leaving a spacetime region. The discussion will be illustrated with examples.
Recording: Link to video Password: 06Zv@N0A
Speaker: Marcos Marino (Universite de Geneve)
Date & Time: 16:30-17:30, Thu Jun 2
Title: Resurgence and quantum topology
Abstract: Quantum field theories and string theories often lead to perturbative series which encode geometric information. In this lecture I will argue that, in the case of complex Chern-Simons theory, perturbative series secretly encode integer invariants, related in some cases to BPS counting. The framework which makes this relation possible is the theory of resurgence, where perturbative series lead to additional non-perturbative sectors, and the integer invariants arise as Stokes constants. I will illustrate these claims with explicit examples related to quantum invariants of hyperbolic knots. If time permits, I will mention similar results in topological string theory.
Slides: Link to slides Recording: Link to video Password: !7f0cXRb
Speaker: Sergei Gukov (Caltech)
Date & Time: 10:00-11:00, Thu May 26
Title: Interesting invariants and TQFTs from 3d-3d correspondence
Abstract: We review recent progress in 3d-3d correspondence, with a focus on new topological invariants and on interesting topological quantum field theories (TQFTs). In particular, we discuss how this line of development can help to bridge topology and quantum topology.
Recording: Link to videoPassword: E5Tiucd.
Speaker: Eric Sharpe (Virginia Tech)
Date & Time: 10:00-11:00, Thu May 19
Title: An introduction to decomposition
Abstract: In this talk I will review work on "decomposition," a property of 2d theories with 1-form symmetries and, more generally, d-dim'l theories with (d-1)-form symmetries. Decomposition is the observation that such quantum field theories are equivalent to ("decompose into") disjoint unions of other QFTs, known in this context as "universes." Examples include two-dimensional gauge theories and orbifolds with matter invariant under a subgroup of the gauge group. Decomposition explains and relates several physical properties of these theories -- for example, restrictions on allowed instantons arise as a "multiverse interference effect" between contributions from constituent universes. First worked out in 2006 as part of efforts to understand string propagation on stacks, decomposition has been the driver of a number of developments since. I will walk through general aspects of 2d gauge theories that exhibit decomposition, dive into specifics in orbifold examples, and as time permits, discuss recent work in progress.
Slides: Link to slides Recording: Link to videoPassword: T$Q4M&KC
Speaker: Zohar Komargodski (SCGP, Stony Brook)
Date & Time: 10:00-11:00, Thu May 5
Title: Comments on Wilson Lines in Massless Gauge Theories
Abstract: We consider the Wilson line operators in certain gauge quantum field theories, including massless QED, massless scalar QED, and N=4 SYM as well as some examples in 2+1d. We find that Wilson lines sometimes admit interesting deformations leading to new conformal line operators. Also, sometimes, Wilson lines are destabilized and lead to an RG flow which we analyze. We also comment on t Hooft lines.
Speaker: Yuji Tachikawa (IPMU, Toyko University)
Date & Time: 10:00-11:00, Thu Apr 28
Title: On the absence of global anomalies of heterotic string theories
Abstract: Superstring theory as we know it started from the discovery by Green and Schwarz in 1984 that the perturbative anomalies of heterotic strings miraculously cancel. But the cancellation of global anomalies of heterotic strings remained an open problem for a long time. In this talk, I would like to report how this issue was finally resolved last year, by combining two developments outside of string theory. Namely, on one hand, the study of topological phases in condensed matter theory has led to our vastly improved understanding of the general form of global anomalies. On the other hand, the study of topological modular forms in algebraic topology allows us to constrain the data of heterotic worldsheet theories greatly, as far as their contributions to the anomalies are concerned. Putting them together, it is possible to show that global anomalies of heterotic strings are always absent.
Slides: Link to slides
Speaker: Nicolai Reshetikhin (YMSC, Tsinghua University)
Date & Time: 16:30-17:30, Thu Apr 21
Title: Superintegrable systems - III
Abstract: The talk will star with an overview of quatntum superintegrability of the spin Calogero-Moser model. Then n-spin CM models will be introduced and it will shown how they are related to two-dimensional Yang-Mills theory.
Slides: Link to slides
Speaker: Nicolai Reshetikhin (YMSC, Tsinghua University)
Date & Time: 16:30-17:30, Thu Apr 14
Title: Superintegrable systems - II
Abstract: First part of the talk is introduction to Hamiltonian integrability. In the second part of the talk their quantum counterparts will be introduced with some examples. Important class of examples is related to moduli spaces of connections over surfaces.
Slides: Link to slides
Speaker: Nicolai Reshetikhin (YMSC, Tsinghua University)
Date & Time: 16:30-17:30, Thu Apr 7, 2022.
Title: Superintegrable systems - I
Abstract: First part of the talk is introduction to Hamiltonian integrability. In the second part of the talk their quantum counterparts will be introduced with some examples. Important class of examples is related to moduli spaces of connections over surfaces.
Slides: Link to slides
Speaker: Eoin Ó Colgáin (CQUeST)
Date & Time: 10:00-11:00, Thu Mar 17, 2022.
Title: Is Hubble constant a constant?
Abstract: Modern cosmology rests upon the Cosmological Principle or FLRW paradigm, namely the assumption that the Universe is isotropic and homogeneous at large scales. Working within these assumptions, we are witnessing a potential 5 sigma discrepancy in the Hubble constant H0 between early and late Universe determinations. I will explain how this discrepancy may be an artifact of a breakdown of FLRW at large scales. If true, we're looking at paradigm shift in cosmology.
Speaker: Bartlomiej Czech (IAS, Tsinghua University)
Date & Time: 16:30-17:30, Thu Mar 3
Title: Holographic Cone of Average Entropies and Universality of Black Holes
Abstract: The holographic entropy cone, which identifies von Neumann entropies of CFT regions that are consistent with a semiclassical bulk dual, is currently known only up to n=5 regions. I explain that average entropies of p-partite subsystems can be checked for consistency with a semiclassical bulk dual far more easily, for an arbitrary number of regions n. This analysis defines the "Holographic Cone of Average Entropies" (HCAE). I conjecture the exact form of HCAE, and find that it has the following properties: (1) HCAE is the simplest it could be, namely it is a simplicial cone. (2) Its extremal rays represent stages of thermalization (black hole formation). (3) In a time-reversed picture, the extremal rays of HCAE represent stages of unitary black hole evaporation, as stipulated by the island solution of the black hole information paradox. (4) HCAE is bound by a novel, infinite family of holographic entropy inequalities. (5) HCAE is the simplest it could be also in its dependence on the number of regions n, namely its bounding inequalities are n-independent. (6) In a precise sense I describe, the bounding inequalities of HCAE unify (almost) all previously discovered holographic inequalities and strongly constrain future inequalities yet to be discovered. I also sketch an interpretation of HCAE in terms of error correction and the holographic Renormalization Group. The big lesson that HCAE seems to be teaching us is about the universality of black hole physics.
Speaker: Jarah Evslin (Institute of Modern Physics)
Date & Time: 16:30-17:30, Thu Feb 24
Title: An Introduction to Schrodinger Wave Functionals
Abstract: Each configuration in a quantum field theory corresponds to a map from a space X of functions or bundles with sections to the space of complex numbers. These maps are called Schrodinger wave functionals. They generalize wave functions in quantum mechanics, which are maps from a finite-dimensional manifold to the complex numbers. We review the main properties of wave functions and wave functionals in a series of examples. We describe an embedding of X into this quantum configuration space and argue that perturbative quantum field theory only probes a tubular neighborhood of its image, but that the poorly understood global properties of the quantum configuration space are relevant to the confinement problem in supersymmetric QCD.
