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 (SM) 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 $⟨{\ensuremath{\sigma}}_{\mathrm{ann}}v{⟩}_{\mathrm{f}}\ensuremath{\lessgtr}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}26}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$. 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.
Highlights
Despite various lines of evidence for the existence of dark matter (DM) [1], its identity remains a major problem at the interface of cosmology and particle physics
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 (SM) 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
Summary
Despite various lines of evidence for the existence of dark matter (DM) [1], its identity remains a major problem at the interface of cosmology and particle physics. An EMD era may be driven by long-lived nonrelativistic quanta that are produced in the postinflationary Universe and dominate the energy density before decaying. This can happen, for example, in models that involve hidden sectors [4,5,6,7]. We present a scenario where a visiblesector particle with a mass around the weak scale drives an EMD era. The parameter space of this scenario may be directly probed at the energy frontier, such as by the proposed searches for long-lived particles at the Large Hadron Collider (LHC) [13,14,15]. Some details of our calculations are presented in the Appendixes
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