Increasing Temperature toward the Completion of Reheating

TL;DR

This paper explores scenarios where the universe's temperature increases during reheating, challenging the common assumption of temperature decrease, with implications for cosmology and particle physics.

Contribution

It derives conditions under which the universe's temperature can rise during reheating and provides concrete scalar field examples demonstrating this phenomenon.

Findings

Temperature can increase during reheating in certain models.

Derived conditions necessary for temperature rise during reheating.

Discussed implications for particle physics and cosmology.

Abstract

Reheating is a process where the energy density of a dominant component of the universe other than radiation, such as a matter component, is transferred into radiation. It is usually assumed that the temperature of the universe decreases due to cosmic expansion even during the reheating process, in which case the maximal temperature of the universe is much higher than the reheat temperature. We point out that the temperature of the universe during reheating may in fact increase in well-motivated scenarios. We derive the necessary conditions for the temperature to increase during reheating and discuss concrete examples involving a scalar field. We comment on implications for particle physics and cosmology due to an increasing temperature during reheating.