Early Matter Domination from Long-Lived Particles in the Visible Sector

TL;DR

This paper proposes a natural scenario where a long-lived visible-sector particle causes early matter domination, diluting relics and aligning with dark matter observations, and can be tested by future particle physics experiments.

Contribution

It introduces a new cosmological model with a long-lived particle causing early matter domination, linking particle physics experiments to early universe history reconstruction.

Findings

Dilution of relics by entropy generation up to 10^4

Compatibility with observed dark matter relic abundance

Potential for experimental probing via long-lived particle searches

Abstract

We show that a nonstandard cosmological history with a period of early matter domination driven by a sub-TeV visible-sector particle can arise rather naturally. This scenario involves a long-lived standard model singlet that acquires a thermal abundance at high temperatures from decays and inverse decays of a parent particle with SM charge(s), and subsequently dominates the energy density of the Universe as a frozen species. Entropy generation at the end of early matter domination dilutes the abundance of dangerous relics (such as gravitinos) by a factor as large as $10^4$. The scenario can accommodate the correct dark matter relic abundance for cases with $\langle \sigma_{\rm ann} v \rangle_{\rm f} \lessgtr 3 \times 10^{-26}$cm$^3$s$^{-1}$. More importantly, the allowed parameter space can be directly probed by proposed searches for neutral long-lived particles at the energy frontier, allowing us to use particle physics experiments to reconstruct the cosmological history just prior to big bang nucleosynthesis.