Abstract
We study production of self-interacting dark matter (DM) during an early matter-dominated phase. As a benchmark scenario, we consider a model where the DM consists of singlet scalar particles coupled to the visible Standard Model (SM) sector via the Higgs portal. We consider scenarios where the initial DM abundance is set by either the usual thermal freeze-out or an alternative freeze-in mechanism, where DM was never in thermal equilibrium with the SM sector. For the first time, we take the effect of self-interactions within the hidden sector into account in determining the DM abundance, reminiscent to the Strongly Interacting Massive Particle (SIMP) scenario. In all cases, the number density of DM may change considerably compared to the standard radiation-dominated case, having important observational and experimental ramifications.
Highlights
The existence of dark matter (DM) seems indisputable
A simple alternative for the standard Weakly Interacting Massive Particles (WIMPs) is provided by relaxing the usual assumption that DM is a thermal relic, produced by the freeze-out (FO) mechanism in the early Universe, and assuming that it never entered in thermal equilibrium with the particles within the Standard Model of particle physics (SM)
We studied different dark matter production mechanisms during an early MD era
Summary
The existence of dark matter (DM) seems indisputable. From the Cosmic Microwave Background radiation (CMB), large scale structure of the Universe and different physics at galactic scales, one can infer that there must be a longlived, dynamically non-hot, non-baryonic matter component, whose abundance exceeds the amount of ordinary ‘baryonic’ matter roughly by a factor of five [1,2,3,4] and which has been there from the hot Big Bang era until the present day. A simple alternative for the standard WIMPs is provided by relaxing the usual assumption that DM is a thermal relic, produced by the freeze-out (FO) mechanism in the early Universe, and assuming that it never entered in thermal equilibrium with the particles within the Standard Model of particle physics (SM). If that was the case, the present DM abundance could have been produced by the so-called freeze-in (FI) mechanism, where the abundance results from decays and annihilations of SM particles into DM [6,7,8,9,10]. We know that the Universe was effectively radiation-dominated (RD) at the time of Big Bang Nucleosynthesis (BBN) and one usually assumes that this was the case at the time the DM component was produced, was it at the time of electroweak cross-over or at higher energy scales. There are no obvious reasons for limiting the DM studies on such cosmological expansion histories, as alternatives can lead to interesting observational ramifications but are
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