MC 6334A

## Candidate

Supranta Sarma Boruah

Applied Mathematics, University of Waterloo

## Title

Topics in early and late time cosmology

## Abstract

In this talk, I will talk about my research on two different epochs of Cosmic evolution.

In the first part, I will talk about some aspects of modification of General Relativity(GR) and its implication for early universe cosmology. General Relativity is a robust framework to describe gravity. Cuscuton was introduced as a minimal modification of gravity, which has since been discovered to emerge in other theories like Massive gravity, Horava gravity. We investigated the perturbative stability of Cuscuton and considered the implications of Cuscuton gravity for early universe cosmology. We discovered that Cuscuton is free from ghosts and other pathologies. We also found a new way of violating the Null Energy Condition(NEC) with Cuscuton.

In the second part, I will talk about my research on observational aspects of determining the distribution of dark matter on galactic and extra-galatic scales. We devised a new way to constrain the potential of the Milky Way using data from ESA's GAIA mission. This makes use of the fact that the merger remnants tend to be clustered in the space of action variables. By maximizing the clustering, we are able to constrain the gravitational potential of the Milky Way. I will also briefly talk about an ongoing project to infer the initial conditions of the universe in a Bayesian manner using the spatial distribution of dark matter halos.