Gravitational wave signals and cosmological consequences of gravitational reheating

TL;DR

This paper explores how gravitational reheating after inflation influences the early universe's evolution and predicts a unique gravitational wave signature detectable by future experiments.

Contribution

It introduces a generic scenario for gravitational reheating with a fluid-like inflaton remnant and derives constraints on inflationary scales from cosmological data.

Findings

Allowed inflationary scale range from CMB and BBN constraints

Predicted primordial gravitational wave spectrum is detectable by upcoming experiments

Scenario results in a distinctive GW signature for observational tests

Abstract

Reheating after inflation can proceed even if the inflaton couples to Standard Model (SM) particles only gravitationally. However, particle production during the transition between de-Sitter expansion and a decelerating Universe is rather inefficient and the necessity to recover the visible Universe leads to a non-standard cosmological evolution initially dominated by remnants of the inflaton field. We remain agnostic to the specific dynamics of the inflaton field and discuss a generic scenario in which its remnants behave as a perfect fluid with a general barotropic parameter $w$. Using CMB and BBN constraints we derive the allowed range of inflationary scales. We also show that this scenario results in a characteristic primordial Gravitational Wave (GW) spectrum which gives hope for observation in upcoming runs of LIGO as well as in other planned experiments.