February 2021

Date: February 3

Time: 17:00 IST (UTC + 5:30)

Speaker: Upamanyu Moitra (TIFR)

Title: Quantisation of Jackiw-Teitelboim Gravity

• Abstract: will talk about the path integral quantisation of the two-dimensional Jackiw-Teitelboim model in the second order formalism — based on joint work with S.K Sake and S.P. Trivedi (hep-th/2101.00596).

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Date: February 8

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

Speaker: Jay Armas (University of Amsterdam)

Title: From black holes to soft matter systems using non-relativistic geometry

• Abstract: I will introduce the description of Newton-Cartan submanifolds and how that can be applied to fluid membranes and soap bubbles. I will explain how these models are related to relativistic models that describe the dynamics of higher-dimensional black holes. I will show examples of how non-relativistic symmetries can be used to describe more generic soft matter systems such as those characterising flocking behaviour.

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Date: February 11

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

Speaker: Michal P. Heller (MPI for Gravitational Physics, AEI Potsdam and National Centre for Nuclear Research)

Title: Spacetime as a quantum circuit

• Abstract: We propose that finite cutoff regions of holographic spacetimes represent quantum circuits that map between boundary states at different times and Wilsonian cutoffs, and that the complexity of those quantum circuits is given by the gravitational action. The optimal circuit minimizes the gravitational action. This is a generalization of both the "complexity equals volume" conjecture to unoptimized circuits, and path integral optimization to finite cutoffs. Using tools from holographic $T\bar{T}$, we find that surfaces of constant scalar curvature play a special role in optimizing quantum circuits. We also find an interesting connection of our proposal to kinematic space, and discuss possible circuit representations and gate counting interpretations of the gravitational action. Based on arXiv:2101.01185.

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Date: February 15

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

Speaker: Giuseppe Policastro (LPENS Paris)

Title: Transport in TTbar-deformed conformal field theories

• Abstract: I will discuss out-of-equilibrium properties of conformal field theories deformed by the TTbar-deformation. Such theories are very interesting because they can describe the effect of an irrelevant perturbation of a critical system, and they are exactly solvable, to some extent. They can be approached from two different point of views: using integrability techniques and the holographic correspondence.I will focus on the energy and momentum Drude weights and diffusion constants, as well as the nonequilibrium steady states which emerge after an inhomogeneous quench. The transport coefficients and nonequilibrium steady state current admit closed form expressions, whose universality is established by the agreement of the two approaches. I will finally discuss the prospects of further extensions of our results.

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Date: February 18

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

Speaker: Bartlomiej Czech (Tsinghua University)

Title: What is the holographic dual to Riemann curvature, and why is it a Berry curvature?

• Abstract: In the AdS/CFT correspondence, the geometry of a bulk AdS spacetime reflects the entanglement structure of its dual (boundary) CFT state. If so, what aspect of CFT entanglement manifests itself as bulk Riemann curvature? The answer is an appropriate generalization of Berry phases (or Berry curvature). While a typical Berry phase is constructed from time-dependent dynamical Hamiltonians, our generalized Berry phase will be constructed from region-dependent "modular" Hamiltonians. A modular Hamiltonian describes how one subsystem is entangled with the rest of the world; the requisite Berry phase will track this information over a continuous family of CFT subregions. A technical prerequisite, which links modular Berry phases to bulk curvature, is the JLMS identification of modular Hamiltonians with generators of boosts orthogonal to extremal (Ryu-Takayanagi) surfaces in the bulk. In addition to bulk Riemann curvature, modular Berry phases can also capture many other properties of bulk spacetimes, including proper time and proper length of non-geodesic trajectories. If time permits, I will describe ongoing research, which further relates modular Berry phases to holographic complexity.

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Date: February 25

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

Speaker: Dongmin Gang (APCTP, Pohang)

Title: M-theoretic genesis of topological phases

• Abstract: will talk about a novel way of constructing (2+1)d topological phases using M-theory. They emerge as macroscopic world-volume theories of M5-branes wrapped on non-hyperbolic 3-manifolds. After explaining the algorithm of extracting modular structures of the topological phase from topological data of the 3-manifold, I will discuss the possibility of full classification of topological orders via the geometrical construction.

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