Doctoral Defense - Rahul Poddar

Doctoral candidate:
Rahul Poddar

Title of thesis:
The TTbar deformation and zeta functions in three-dimensional gravity

Opponents:
Dr. Alejandra Castro, Associate Professor, University of Cambridge, UK Daniel Grumiller, Associate Professor, TU Wien, Austria.

Advisor:
Dr. Lárus Thorlacius, Professor at the University of Iceland, Faculty of Physical Sciences.

Also in the doctoral committee:
Dr. Valentina Giangreco M. Puletti, Professor, University of Iceland, Faculty of Physical Sciences, Monica Guica, Researcher at the Institut de Physique Théorique, CEA Saclay, France.

Chair of Ceremony:
Dr. Einar Örn Sveinbjörnsson, Professor and Head of the Faculty of Physical Sciences at the University of Iceland.

Abstract:
This thesis explores two topics in three-dimensional gravity, the TTbar deformation and zeta functions of three-dimensional quotient manifolds. The TTbar deformation is an irrelevant deformation of a two-dimensional translationally invariant quantum field theory which is well-behaved in the UV. We consider the case of two-dimensional holographic Warped Conformal Field theories (WCFTs), which are dual to gravity in three-dimensional anti-de Sitter (AdS3) spacetime with Compere, Song, Strominger (CSS) boundary conditions. WCFTs are non-relativistic quantum field theories which have a Virasoro x U(1) Kac-Moody symmetry algebra. We compute the boundary conditions and asymptotic symmetry algebra for a TTbar deformed WCFT. We find that the U(1) Kac-Moody algebra survives the deformation if one allows the boundary metric to transform appropriately under the asymptotic symmetries, however the Virasoro sector becomes highly deformed and is no longer chiral. The Selberg zeta function is defined by the Euler product over prime geodesics on a hyperbolic quotient manifold. It provides a simpler way to compute functional determinants of kinetic operators compared to traditional means. We introduce a new construction of a zeta function, which generalizes the Selberg zeta function to non-hyperbolic quotient manifolds. We employ our generalization to quotients of three-dimensional Warped AdS3 and three-dimensional flat spacetime. We find that the zeroes of the zeta function accurately predicts the quasinormal mode spectrum in these non-hyperbolic cases, providing evidence for the proposed construction of the zeta function.

About the candidate:
Rahul is a Ph.D candidate in physics at the University of Iceland. He obtained his Bachelor's and Master's degree in Physics from the Indian Institute of Science Education and Research, Pune, India in 2020. His research interests involve quantum field theory and holographic aspects of quantum gravity, with particular emphasis on two-dimensional conformal field theories and their deformations.