Cosmological Signatures of Some Beyond Standard Model Physics Scenarios

Abstract

This thesis investigates well-motivated beyond the Standard Model scenarios whose signatures are challenging to probe in laboratory experiments but can be explored through cosmological and astrophysical observations. It focuses on the imprints of dark sector physics on the cosmic microwave background, the role of primordial black holes in generating dark radiation and stochastic gravitational waves, and high-energy astrophysical messengers. Together, these observables provide complementary probes of new physics in the early Universe.