Cosmic Laboratory of Particle Physics

Abstract

Cosmological observations have entered the era of precision, unlocking its tremendous power as a particle physics laboratory, aiding our search for physics beyond the Standard Model. The great power of cosmology comes from its great range of possibility. Processes far beyond the reach of terrestrial apparatus are possible as the universe scans through orders of magnitude of energy throughout its evolution. On the flip side, the great range of possibility also implies a tremendous difficulty to extract information: without knowing precisely what we are looking for, the cosmological data itself provides little hint of what the underlying particle theory might be. This thesis presents several work on the early universe signatures of physics beyond the Standard Model, clarifying the cosmological consequences of various particle physics scenarios. We show how interaction with light scalars of heavy particles during inflation could lead to space-dependent mass corrections, that appear as loss of correlation in the three-point correlation function of the curvature perturbation mediated by the heavy particles. We also discuss how a similar change in the underlying particle physics model, where we add one additional layer of particle interaction, could alleviate backreaction effect and lead to orders of magnitude change in the energy transfer efficiency in preheating after inflation. We will then study how information about underlying particle physics can be buried in the correlation between multiple cosmological observables, specifically in the case of curvaton models generating large local-type non-Gaussianity. Finally, we present a case where there is a close interplay between high energy considerations from quantum gravity, which prohibits the existence of global symmetries, and cosmology, in the context of Nelson-Barr-type solutions to the strong CP problem. We show that restriction on the scale of CP breaking due to the quality problem in Nelson-Barr-type models necessarily prohibits high scale inflation, and we provide an example of an extended Nelson-Barr-type model that restores this possibility.