From Inflation to the Hot Big Bang: Nonperturbative Aspects of Reheating and Its Signatures on Cosmic Relics

概要

The early universe is regarded as an ideal laboratory for the generation of all kinds of elementary particles (Standard Model

(SM) and beyond the Standard Model (BSM)), populating the present universe. An intermediate phase, which bridges the gap in energy and time scales between the end of inflation and the beginning of the hot Big Bang, is the post-inflationary reheating phase. The absence of direct observational evidence has left this important phase of the early universe poorly constrained, both at present and in the foreseeable future. However, the distinct imprints of this phase on cosmic relics offer us a promising avenue for its indirect probe through various cosmological observables.

The early inflation and post-inflationary reheating phases are an important playground for investigating various non-perturbative, non-equilibrium phenomena. Parametric resonance and tachyonic instability are some distinctive features of the non-perturbative phenomena in the early era. For instance, in the early reheating era (Preheating), plenty of elementary particles were produced within a very short period through the mechanism of parametric resonance instability, when the interaction strength between the inflaton and the daughter particles is appropriate. Another notable aspect where non-perturbative effects become instrumental is the Cosmological Gravitational Particle Production (CGPP). This CGPP is the quantum mechanical particle production in a time-dependent dynamical background. Unlike Preheating, in CGPP, the background dynamics during reheating itself causes particle production without any direct coupling to the inflaton. These particles can play an important role in cosmic history, being possible candidates for dark matter, gravitational wave radiation, dark radiation, etc.   This talk sheds light on various non-perturbative signatures of gravitational particle production, both in minimalistic (no coupling to gravity) and non-minimalistic (non-zero coupling to gravity) scenarios.

We have made unprecedented progress in observational cosmology after the detection of gravitational waves. In this talk, one of the prime objectives is to decipher various non-perturbative signatures of different early universe phenomena through their discernible imprint on gravitational waves. These ideas present the main theme of my presentation.

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