Abstract
The existence of dark matter particles that carry phenomenologically relevant self-interaction cross sections mediated by light dark sector states is considered to be severely constrained through a combination of experimental and observational data. The conclusion is based on the assumption of specific dark matter production mechanisms such as thermal freeze-out together with an extrapolation of a standard cosmological history beyond the epoch of primordial nucleosynthesis. In this work, we drop these assumptions and examine the scenario from the perspective of the current firm knowledge we have: results from direct and indirect dark matter searches and cosmological and astrophysical observations, without additional assumptions on dark matter genesis or the thermal state of the very early universe. We show that even in the minimal set-up, where dark matter particles self-interact via a kinetically mixed vector mediator, a significant amount of parameter space remains allowed. Interestingly, however, these parameter regions imply a meta-stable, light mediator, which in turn calls for modified search strategies.
Highlights
Cold dark matter (DM) contributes 26% to the present day energy budget of the universe
A third, and not mutually excluding possibility, may be that those pertinent small-scale problems point to new dynamics in the dark sector, in particular to the possibility that DM particles χ self-interact with sizable nongravitational strength [37,38]
Requiring that the selfinteraction cross section is of suitable strength, we obtain the parameter space that is allowed by current direct DM searches, and by astrophysical and cosmological observations once we couple the dark sector to the standard model (SM)
Summary
Cold dark matter (DM) contributes 26% to the present day energy budget of the universe. Among particle physics models which can produce such large self-interaction cross sections are the scenarios where self-interactions are mediated by light states [37,53,54,55,56] Such scenarios have been tightly constrained by linking the experimental observations with the assumption that DM particles stay in thermal contact with the SM bath before they freeze out (e.g., [57,58,59,60,61,62]). (2) we require that at T ≳ 1 eV the DM abundance has matched onto the CMB-observed value, while acknowledging the possibility that additional restrictions in the window 1 eV < T < 1 MeV may apply Based on these assumptions, and requiring that the selfinteraction cross section is of suitable strength, we obtain the parameter space that is allowed by current direct DM searches, and by astrophysical and cosmological observations once we couple the dark sector to the standard model (SM).
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