Dark Freeze-out Cogenesis

Abstract

We propose a new mechanism where a multi-component dark sector generates the observed dark matter abundance and baryon asymmetry and thus addresses the coincidence between the two. The thermal freeze-out of dark matter annihilating into meta-stable dark partners sets the dark matter relic abundance while providing the out-ofequilibrium condition for baryogenesis. The meta-stable state triggers baryon asymmetry production by its decay well after the freeze-out and potentially induces a period of early matter domination before its decay. The dark matter and baryon abundances are related through number conservation within the dark sector (cogenesis). The "coincidence" is a natural outcome with GeV-to TeV-scale symmetric dark matter and the dark sector's interactions with the Standard Model quarks. We present a UV-complete model and explore its phenomenological predictions, including dark matter direct detection signals, LHC signatures of new massive particles with color charges and long-lived particles with displaced vertices, dark matter-induced nucleon conversions, (exotic) dark matter indirect detection signals, and effects on the cosmological matter power spectrum. As a side result, we provide a novel analytical treatment for dark sector freeze-out, which may prove useful in the study of related scenarios.

Early-Universe Model Building

“…WIMP (e.g. [725][726][727][728]). These scenarios yield new opportunities for explaining the observed coincidence Ω DM ∼ 5Ω B between the DM and baryon abundances.…”

“…Recent developments related to this scenario include, for instance, WIMP Cogenesis and Dark Freezeout Cogenesis [727,728]. In the former [727] of these models, the decay of the WIMP grandparent simultaneously generates DM and baryon asymmetries.…”

“…Through renormalizable interactions with quarks, the DM candidate is within reach future iterations of DarkSide [729] and other upcoming direct detection experiments. In the latter [728] of these new models, the DM-baryon coincidence is achieved with number conserving interactions between stable and metastable DM partners in a hidden sector. Number conservation relates the partners' abundances at their freeze-out.…”

Ultraviolet freeze-in baryogenesis

“…[1,2]), the observed DM cosmic abundance is viewed as being due to an asymmetry being created between the abundances of DM and dark anti-matter which survived after the symmetric component annihilated away, in a manner similar to (and, typically, connected with) the asymmetry between baryons and anti-baryons in the visible sector. In scenarios of baryogenesis via weekly interacting massive particles ("WIMPy baryogenesis") [3][4][5][6], on the other hand, there is no asymmetry in the dark sector and the observed baryon asymmetry is generated during the freeze-out of DM particles, once they fall out of equilibrium with the thermal plasma.…”