Chennai Mathematical Institute


Date and Time: Friday, 22 October 2021, 11.30 am
Perturbative and non - perturbative aspects of quantum gravity

A. Manu
Chennai Mathematical Institute.


This thesis is a study in some aspects of perturbative and non - perturbative aspects of quantum gravity. It is divided into two parts.

The first part is an investigation into the connection between a remarkable symmetry of Gluon scattering amplitudes known as color kinematics duality and a mysterious map known as classical double copy. Classical double copy is an intriguing relationship between classical solutions to a gravity theory and solutions to classical Yang-Mills equations. Although formally inspired by the double copy relation between (quantum) scattering amplitudes in Yang-Mills and perturbative gravity, a direct proof of the former from the latter continues to be under investigation. In the first part of the thesis we attempt to prove classical double copy from the color-kinematics duality symmetry of scalar QCD amplitudes in a restricted setting. That is, we consider radiative solutions with classical scattering sources in Yang-Mills theory and perturbative gravity in D 4 spacetime dimensions. We show that when the frequency of radiation is much smaller than the characteristic frequency of the process, then at the subleading order in frequency, the classical double copy relating radiative gluon field to radiative gravitational field can be proved from the color-kinematics duality of scalar QCD amplitudes.

In the second part we study aspects of entanglement and extremal surfaces in various families of spacetimes exhibiting cosmological, Big-Crunch singularities, in particular isotropic AdS Kasner. The classical extremal surface dips into the bulk radial and time directions. Explicitly analysing the extremization equations in the semiclassical region far from the singularity, we find the surface bends in the direction away from the singularity. In the 2-dim cosmologies obtained by dimensional reduction of these and other singularities, we have studied quantum extremal surfaces by extremizing the generalized entropy. The resulting extremization shows the quantum extremal surfaces to always be driven to the semiclassical region far from the singularity.