Warm and Cold Dark Matter in Bouncing Universe

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.