Warm and Cold Dark Matter in Bouncing Universe

TL;DR

This paper explores how a new dark matter candidate, EQFIDM, can be produced in bouncing cosmology, with different decay types leading to warm or cold dark matter, consistent with current observations and potentially addressing small-scale structure issues.

Contribution

It introduces a model-independent formalism for entropy-producing decay processes of residual bouncing fields, expanding the viable parameter space for EQFIDM in bouncing universe scenarios.

Findings

Five decay types are compatible with current observations.

The particle mass of EQFIDM can vary from sub-keV to super-TeV.

EQFIDM may help alleviate small-scale structure problems.

Abstract

Being free from the initial singularity, bouncing cosmology serves as a promising alternative to inflation. However, the entropy production during the post-bounce phase is still unclear. In this work, we use a newly unveiled DM candidate (EQFIDM), which can directly freeze in thermal equilibrium shortly after bounce, to trace the entropy-producing decay process of residual bouncing field (RBF). Specifically, we present a model-independent formalism to obtain all nine possible types of the entropy-producing decay of RBF within a generic bouncing universe, and show that, due to the entropy productions in different types, the particle mass of this new candidate can range from sub-keV scale to super-TeV scale. With current Lyman-$\alpha$ forest observation on linear matter spectrum, we find that, although four types have been excluded, the rest five types, which suggest warm and cold EQFIDM candidates with effective entropy productions, are accommodated with current observation. Then we illustrate how the nature of RBF can be constrained by current observation and investigate the potential of EQFIDM on alleviating small-scale crisis.