Light Dark Matter from Inflaton Decay

TL;DR

This paper introduces a mechanism where light dark matter produced from inflaton decay can be cold enough to evade warm dark matter constraints, even at small masses, by suppressing its momentum through specific decay conditions.

Contribution

It presents a novel decay-based production mechanism for light dark matter that results in cold, abundant particles compatible with observational constraints.

Findings

Dark matter produced from inflaton decay can be sufficiently cold.

The mechanism applies to both bosonic and fermionic dark matter.

Viable dark matter candidates include axions and right-handed neutrinos.

Abstract

We propose a simple mechanism of light dark matter (DM) production from the decay of the oscillating inflaton condensation. If the reheating temperature after inflation is higher than the inflaton mass, which is of the same order of the momentum of the DM at the time of the production, the DM momentum can be suppressed compared to the temperature of the thermal plasma if the interaction of the DM is weak enough. Consequently, the DM can be cold enough to avoid the observational constraints on the warm DM, like the Lyman-$\alpha$ bound even if the DM mass is small. We study the bosonic and fermionic DM production from the inflaton decay, taking into account the effect of the stimulated emission and Pauli blocking, respectively. In both cases, the DM can be cold and abundant enough to be a viable candidate of the DM. We also apply our mechanism to the production of isocurvature-problem-free axion DM and Dirac sea DM of right-handed neutrino consistent the seesaw relation for the active neutrino masses.