Manifesting hidden dynamics of a sub-component dark matter

TL;DR

This paper explores how a sub-component of dark matter with significant self-scattering affects cosmological evolution and detection prospects, revealing that smaller abundance fractions can be more detectable despite being harder to produce.

Contribution

It demonstrates the impact of self-scattering on sub-component dark matter dynamics and shows that detection likelihood increases as the abundance fraction decreases, challenging naive expectations.

Findings

Smaller abundance fractions (<10%) are strongly constrained by current experiments.

Self-scattering significantly alters the thermal evolution of sub-component dark matter.

Warm dark matter constraints complement accelerator-based searches for larger abundance fractions.

Abstract

We emphasize the distinctive cosmological dynamics in multi-component dark matter scenarios and its impact in probing a sub-dominant component of dark matter. We find that the thermal evolution of the sub-component dark matter is significantly affected by the sizable self-scattering that is naturally realized for sub-${\rm GeV}$ masses. The required annihilation cross section for the sub-component sharply increases as we consider a smaller relative abundance fraction among the dark-matter species. Therefore, contrary to a naive expectation, it can be easier to detect the sub-component with smaller abundance fractions in direct/indirect-detection experiments and cosmological observations. Combining with the current results of accelerator-based experiments, the abundance fractions smaller than $10\,\%$ are strongly disfavored; we demonstrate this by taking a dark photon portal scenario as an example. Nevertheless, for the abundance fraction larger than $10\,\%$, the warm dark matter constraints on the sub-dominant component can be complementary to the parameter space probed by accelerator-based experiments.