September 2021

Date: September 2

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

Speaker: Debajyoti Sarkar (IIT Indore)

This talk is a part of the activities of the Center for Quantum Information Theory of Matter and Spacetime of IIT Madras

Title: Light-ray moments as endpoint contributions to modular Hamiltonians

• Abstract: We consider excited states in a CFT, obtained by applying a weak unitary perturbation to the vacuum. The perturbation is generated by the integral of a local operator of modular weight over a spacelike surface passing through x = 0. For n \geq 2, the modular Hamiltonian associated with a division of space at x =0 picks up an endpoint contribution, sensitive to the details of the perturbation at x=0. The endpoint contribution is a sum of light-ray moments of the perturbing operator J^{(n)} and its descendants. For perturbations on null planes only moments of J^{(n)} itself contribute. Work based on https://arxiv.org/abs/2006.13317 and https://arxiv.org/abs/2103.08636.

VIDEO: Click here

Date: September 3

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

Speaker: B Ananthanarayan (IISc Bengaluri)

This was a special hep-th colloquium

Title: (g-2) of the muon: Theory and experiment challenge one another

• Abstract: The muon is a heavy cousin of the electron and has a gyromagnetic ratio of 2 in the classical limit, which was predicted by Dirac. In QED it receives an anomalous magnetic moment which was computed by Julian Schwinger at leading order. Today, in QED it is evaluated to very high loop order, and also receives corrections from virtual processes in the vacuum as dictated by the laws of quantum field theory, which have to be evaluated in a variety of ways. It is also measured at high precision today at Fermilab, whose recent results confirm the value measured at Brookhaven about 20 years ago. More data is being gathered to lower the uncertainty. The theoretical value which is known at high precision deviates from the experimental measurement at several standard deviations. The quantity is also measured on the lattice with larger errors. In this talk we will review these developments and also speak about our own results that have played an important role in lowering the uncertainties in the theoretical hadronic vacuum polarization contributions.

VIDEO: Click here

Date: September 9

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

Speaker: Masanori Hanada (University of Surrey)

This talk is a part of the activities of the Center for Strings, Gravitation and Cosmology of IIT Madras

Title: Confinement/deconfinement transition in the D0-brane matrix model -- A signature of M-theory?

• Abstract: We study the confinement/deconfinement transition in the D0-brane matrix model (often called the BFSS matrix model) and its plane-wave deformation (the BMN matrix model) numerically by lattice Monte Carlo simulation. Our results confirm general expectations from the dual string/M-theory picture for strong coupling. We suggest that these models provide us with an ideal framework to study the Schwarzschild black hole, M-theory, and furthermore, the parameter region between type IIA superstring theory and M-theory. A detailed study of M-theory via Monte Carlo simulation of the D0-brane matrix model might be doable with much smaller computational resources than previously expected. This talk is based on a paper in preparation with Bergner, Bodendorfer, Pateloudis, Rinaldi, Schaefer, Vranas, and Watanabe (Monte Carlo String/M-theory Collaboration).

VIDEO: Click here

Date: September 16

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

Speaker: Tanay Kibe (IIT Madras)

This talk is a part of the activities of the Center for Quantum Information Theory of Spacetime and Matter of IIT Madras

Title: Quantum thermodynamics of holographic quenches and bounds on entanglement growth from QNEC

• Abstract: The quantum null energy condition (QNEC) is a lower bound on the energy-momentum tensor in terms of the variation of the entanglement entropy of a subregion along a null direction. Motivated by recent studies of quantum thermodynamics, we study if the QNEC restricts quenches in holographic many-body systems. We find that an increase in entropy and temperature is necessary but not sufficient to not violate QNEC in quenches that lead to transitions between BTZ geometries dual to thermal states carrying angular momentum. For an arbitrary initial thermal state, we can determine the lower and upper bounds on the temperature (entropy) increase that is necessary for a fixed increase in entropy (temperature) in order to satisfy the QNEC. Our study shows that the entanglement entropy thermalizes in time l/2 where l is the length of the entangling region with an exponent 3/2 for an arbitrary allowed transition generalizing earlier results. Furthermore we are able to determine the rate of initial quadratic growth exactly for any transition as a function of l and show that the QNEC bounds it. We also show that for a semi-infinite region the slope of the ballistic growth of entanglement at late time is simply twice the difference of the entropy densities of the final and initial states in consistency with the eigenstate thermalization hypothesis. We show that our methods can shed light on the validity of Landauer erasure principle, the design of quantum engines and more generally on the applicability of quantum resource theories in holographic many-body systems. This talk is based on upcoming papers in collaboration with Avik Banerjee, Nehal Mittal, Ayan Mukhopadhyay and Pratik Roy.

VIDEO: Click here

Date: September 23

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

Speaker: Alexandre Belin (CERN)

This talk is a part of the activities of the Center for Quantum Information Theory of Spacetime and Matter of IIT Madras

Title: Bootstrapping Quantum Extremal Surfaces

• Abstract: Quantum extremal surfaces are central to the connection between quantum information theory and quantum gravity and they have played a prominent role in the recent progress on the information paradox. In this talk, I will present a program to systematically link these surfaces to the microscopic data of the dual conformal field theory, namely the scaling dimensions of local operators and their OPE coefficients. I will consider CFT states obtained by acting on the vacuum with single-trace operators, which are dual to one-particle states of the bulk theory. Focusing on AdS3/CFT2, I will compute the CFT entanglement entropy to second order in the large c expansion where quantum extremality becomes important and match it to the expectation value of the bulk area operator. I will show that to this order, the Virasoro identity block contributes solely to the area operator.

VIDEO: Click here

Date: September 27

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

Speaker: Sukanya Mitra (TIFR)

This talk is a part of the activities of the Center for Strings, Gravitation and Cosmology of IIT Madras

Title: Correspondence between momentum-dependent relaxation time and field redefinitions in relativistic hydrodynamics

• Abstract: A correspondence has been established between the out of equilibrium system dissipation and the thermodynamic field redefinition of the macroscopic variables through the momentum dependent relaxation time approximation (MDRTA) solution of relativistic transport equation. Here, it has been shown that the out of equilibrium thermodynamic fields are not uniquely defined and are subjected to include dissipative effects from the medium. A second order relativistic hydrodynamic theory has been developed including such dissipative effects. The necessary conditions for developing a hydrodynamic theory has been fulfilled, (i) the thermodynamic identities incorporating such redefined fields have been shown to conserve the energy-momentum tensor perfectly under MDRTA, (ii) the non-negativity of entropy production remains unaffected by the inclusion of such dissipative contributions in hydro fields as long as the independent transport coefficients remain positive. Finally, a scheme has been proposed to develop the entire formalism with general matching conditions without imposing any specific hydrodynamic frame choice.

VIDEO: Click here

Date: September 30

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

Speaker: Onkar Parrikar (TIFR)

This talk is a part of the activities of the Center for Quantum Information Theory of Matter and Spacetime of IIT Madras

Title: Quantum error correction in the Black hole interior

• Abstract: We study the quantum error correction properties of the black hole interior in a toy model for an evaporating black hole in JT gravity entangled with a non-gravitational bath. It has recently been shown that past the Page time, the black hole interior lies in the entanglement wedge of the bath, and thus the bulk degrees of freedom in the interior are encoded in the bath Hilbert space. We discuss the error correction properties of this encoding against quantum operations on the bath and show that the encoding is robust against a large class of such quantum operations which (i) do not have access to microstate details, and (ii) have coherent information bounded from below by minus the black hole entropy. This implies that the encoding of the black hole interior in the radiation is robust against generic, low-rank quantum operations on the bath, providing a gravitational perspective on the recent results of Kim, Preskill and Tang.

VIDEO: Click here