May 2021

Date: May 6

Time: 17:30 IST (UTC + 5:30)

Speaker: Parijat Dey (Uppsala University)

Title: Constraining Conformal Field theories

• Abstract: Conformal field theories describe the universal physics of scale invariant critical systems. A theoretical description of these strongly coupled systems is a challenging task since the standard tools of perturbative quantum field theory cannot be applied. Such systems can be studied using symmetries and other consistency conditions in a Lagrangian free approach which is known as conformal bootstrap. This is a self-consistent condition that relies entirely on the conformal symmetry. We show how conformal bootstrap has emerged as a viable tool to explore critical systems in the context of Wilson-Fisher theory at the fixed point. We discuss a dispersion relation in conformal field theory which expresses the correlation function as an integral over its discontinuity. Exploiting the analytic properties and crossing symmetry of the correlator, we compute the correlator perturbatively in the Wilson-Fisher theory.

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Date: May 7

Time: 9:30 IST (UTC + 5:30)

Speaker: Prabha Mandayam (IIT Madras)

Title: The Petz map: from open quantum systems to holography (Part 2)

• Abstract: Originally introduced as a map that approximately preserves quantum information in open quantum systems, the Petz map has today emerged an important tool in the context of holographic models. In this talk we will review the various manifestations of the Petz map as a universal recovery channel: from approximate quantum error correction to bulk reconstruction in random tensor networks. Along the way, we will also touch upon a key information-theoretic application of the Petz construction, namely, in identifying the class of states that saturates the strong subadditivity inequality of the von Neumann entropy.

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Date: May 10

Time: 17:30 IST (UTC + 5:30)

Speaker: Takaaki Ishii (Kyoto University)

Title: Superradiant instability and black resonators

• Abstract: Rotational superradiance by a Kerr or Myers-Perry black hole can lead to superradiant instability in an asymptotically AdS space. It has been found that time-periodic black holes branch off from the onset of gravitational superradiant instability, and they are named black resonators. In this talk, I will consider the 5D equal-spinning Myers-Perry black hole and obtain a black resonator given by a cohomogeneity-1 metric. I will also include a scalar field on top of the black resonator and obtain a hairy black resonator as a black resonator equipped with scalar hair. This talk is based on arXiv:2101.06325.

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Date: May 13

Time: 20:00 IST (UTC + 5:30)

Speaker: Eva Silverstein (Stanford University)

Title: Hyperbolic compactification of M theory and de Sitter quantum gravity

Abstract: We present a mechanism for accelerated expansion of the universe in the generic case of negative-curvature compactifications of M-theory, with minimal ingredients. M-theory on a hyperbolic manifold with small closed geodesics supporting Casimir energy -- along with a single classical source (7-form flux) -- contains an immediate 3-term structure for volume stabilization at positive potential energy. Hyperbolic manifolds are well-studied mathematically, with an important rigidity property at fixed volume. They and their Dehn fillings to more general Einstein spaces exhibit explicit discrete parameters that yield small closed geodesics supporting Casimir energy. The off-shell effective potential derived by M. Douglas incorporates the warped product structure via the constraints of general relativity, screening negative energy. Analyzing the fields sourced by the localized Casimir energy and the available discrete choices of manifolds and fluxes, we find a regime where the net curvature, Casimir energy, and flux compete at large radius and stabilize the volume. Further metric and form field deformations are highly constrained by hyperbolic rigidity and warping effects, leading to calculations giving strong indications of a positive Hessian, and residual tadpoles are small. We test this via explicit back reacted solutions and perturbations in patches including the Dehn filling regions, initiate a neural network study of further aspects of the internal fields, and derive a Maldacena-Nunez style no-go theorem for Anti-de Sitter extrema. A simple generalization incorporating 4-form flux produces axion monodromy inflation. As a relatively simple de Sitter uplift of the large-N M2-brane theory, the construction applies to de Sitter holography as well as to cosmological modeling, and introduces new connections between mathematics and the physics of string/M theory compactifications.

Date: May 17

Time: 17:30 IST (UTC + 5:30)

Speaker: Kostas Skenderis (University of Southampton)

Title: Holographic cosmology and the resolution of the initial singularity

• Abstract: Holographic cosmology is a new framework for the very early universe, the period usually associated with inflation. In holographic cosmology the early Universe is described by a three dimensional QFT, and cosmological evolution is mapped to inverse RG flow. In this talk, I will provide an overview of holographic cosmology and then discuss recent work where lattice QFT methods are used to compute the relevant QFT observables. In particular, I will discuss the IR structure of the dual QFT, which is linked to the question of the resolution of the initial singularity in cosmology, and show how non-pertubative dynamics resolve the IR singularities which are present in perturbation theory, thus providing a holographic resolution of the Big Bang singularity

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Date: May 24

Time: 17:30 IST (UTC + 5:30)

Speaker: Jim Libby (IIT Madras)

Title: B anomalies: an experimental perspective

• Abstract: The first part of the talk will review the current status of the so-called ‘$B$ anomalies’. These anomalies are principally in $b\to s\ell^+\ell^-$ and $b\to c \tau^-\bar{\nu}_{\tau}$ transitions; the differing character of these two processes from both a phenomenological and experimental point of view will be emphasised. The latter part of the talk will discuss the future prospects for measurements at LHCb, Belle II and elsewhere that will either crystalize or refute these anomalies.

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Date: May 27

Time: 09:30 IST (UTC + 5:30)

Speaker: Mark van Raamsdonk (University of British Columbia)

Title: Cosmology From Confinement

• Abstract: We describe a class of holographic models that may describe the physics of certain four-dimensional big-bang/big-crunch cosmologies. The construction involves a pair of 3D Euclidean holographic CFTs coupled at either end of an interval to a Euclidean 4D CFT with many fewer local degrees of freedom. We argue that in some cases, the theory flows to a gapped/confining three-dimensional field theory in the infrared, and this is reflected in the dual description by the asymptotically AdS spacetimes dual to the two 3D CFTs joining up in the IR to give a Euclidean wormhole. The Euclidean construction can be reinterpreted as generating a state of Lorentzian 4D CFT on whose dual includes the physics of a big-bang/big-crunch cosmology

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Date: May 31

Time: 09:30 IST (UTC + 5:30)

Speaker: Benjamin Doyon (King's College London)

Title: The hydrodynamics of many-body integrable systems

• Abstract: Hydrodynamics is a powerful theory for the emergent behaviours at large scales of space-time in many-body systems. The theory says that only few degrees of freedom are sufficient in order to describe what is observed at such scales, and it provides equations for the dynamics of these degrees of freedom. Think of the simple water waves emerging from the motion and interaction of a myriad of water molecules. It is strongly based on the presence of microscopic conservation laws in the many-body model, such as conservation of energy, momentum and mass. But the standard equations of hydrodynamics fail to describe one-dimensional integrable systems, including the ultracold atomic gases observed in experiments. Integrable systems admit an extensive number of conservation laws, which must be taken into account in the emergent hydrodynamic theory. Recently this theory, dubbed ``generalised hydrodynamics”, has been developed. In this talk, I will review fundamental aspects of hydrodynamics and the main idea and equations of generalised hydrodynamics. I will discuss recent cold-atom experiments that confirm the theory, some of the exact results that can be obtained with this formalism such as nonequilibrium steady states and asymptotic of correlation functions, and if time permit some mathematically rigorous results in these directions.

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