Gravitational reheating through conformally coupled superheavy scalar particles

TL;DR

This paper investigates gravitational production of superheavy conformally coupled scalar particles during the transition from inflation to kination, showing they can be abundantly produced and contribute to reheating.

Contribution

It provides exact and numerical solutions for particle production without adiabatic approximation, highlighting conditions for abundant superheavy particle creation.

Findings

Superheavy particles can be produced abundantly if transition time is short.

Reheating temperature formulas are derived for different decay scenarios.

Production is significant even for particles heavier than the Hubble scale.

Abstract

We calculate the number density and the energy density of a massive scalar particle conformally coupled to gravity produced by gravitational particle creation in the case the kination stage follows inflation. In this model, mode functions are derived in terms of exact or numerical solutions of the equation of motion without using the adiabatic approximation. We define the adiabatic vacuum in each stage and calculate the produced number density and the energy density. The resultant power spectra show that even the superheavy particle which is as heavy as or much heavier than the Hubble scale during inflation can be produced abundantly if the transition time scale from inflation to the kination stage is smaller than the inverse of the mass of the scalar field. We also give simple forms of the reheating temperature for two cases, one that the produced scalar particles decay instantly and the other that they decay when their energy density exceeds that of inflaton.