Aspects of early universe cosmology: gravitational waves and cosmological model selection

by Ameek Malhotra

Thursday 14 Nov 2024, 16:00 → 17:00 Australia/Sydney

This talk will be divided into two parts. In the first part of this talk, I will discuss the recent evidence for a stochastic gravitational wave background (SGWB) as seen by pulsar timing arrays (PTAs) and its interpretation as a signal of early-universe origin. I will highlight the role of SGWB anisotropies, focusing in particular on kinematic anisotropies, as a diagnostic tool to identify if the observed SGWB is of early-universe or astrophysical origin. The second part of the talk deals with the issue of cosmological model selection in the framework of Bayesian inference. This requires the computation of the Bayesian evidence, which can be highly challenging if the underlying cosmological likelihood is expensive to evaluate. I will discuss how a technique called Bayesian Optimization, based on Gaussian Process regression, can be used to calculate this evidence in far fewer likelihood evaluations, offering a much more efficient approach compared to traditional methods.