PhD Comprehensive Exam | Supranta Sarma Boruah, Theoretical and observational constraints on the origin of the universe

MC-6334A

Candidate

Supranta Sarma Boruah | Applied Math, University of Waterloo

Title

Theoretical and observational constraints on the origin of the universe

Abstract

Current standard model of cosmology is based on the paradigm of inflation, where the universe began with an exponential expansion. In the absence of a fundamental quantum theory of gravity, we need to rely of effective field theories(EFTs) to make predictions for inflationary observables. We plan to examine the robustness of inflationary observables to quantum corrections in a specific class of inflationary models. Inflation also requires a phase of reheating, where the energy in the inflaton is transferred to the standard model particles. Reheating produces a large number of particles due to a phenomenon called parametric resonance. It has been shown that in certain toy models of multi-field inflation, the isocurvature perturbations are also parametrically amplified. We use this phenomenon to potentially put constraints on certain models of multi-field inflation, which generically produce isocurvature perturbations.

In the second part of my talk, I will talk about putting constraints on the initial phase of evolution of the universe using the large-scale structure observations. There are a broad class of techniques known as reconstruction, which is used for this purpose. We use a Bayesian forward modelling technique, where the initial conditions are evolved to the future using some simple technique such as Lagrangian perturbation theory(LPT). The evolved Lagrangian density is compared statistically with the observed halos. We developed a probabilistic model for the inference of the initial density perturbation in the universe. The initial conditions thus can be inferred in a Bayesian sense after a number of iterations of this process. We plan to test our method on simulations and mock galaxy catalogs before applying this technique to real galaxy catalogs in a future work.