Abstract
The cold dark matter (CDM) candidate with weakly interacting massive particles can successfully explain the observed dark matter relic density in cosmic scale and the large-scale structure of the Universe. However, a number of observations at the satellite galaxy scale seem to be inconsistent with CDM simulation. This is known as the small-scale problem of CDM. In recent years, it has been demonstrated that self-interacting dark matter (SIDM) with a light mediator offers a reasonable explanation for the small-scale problem. We adopt a simple model with SIDM and focus on the effects of Sommerfeld enhancement. In this model, the dark matter candidate is a leptonic scalar particle with a light mediator. We have found several regions of the parameter space with proper masses and coupling strength generating a relic density that is consistent with the observed CDM relic density. Furthermore, this model satisfies the constraints of recent direct searches and indirect detection for dark matter as well as the effective number of neutrinos and the observed small-scale structure of the Universe. In addition, this model with the favored parameters can resolve the discrepancies between astrophysical observations and $N$-body simulations.
Highlights
The first evidence of dark matter (DM) was observed by Fritz Zwicky [1] in 1933
We have found favored regions of the parameter space with proper masses and coupling strength generating a relic density that is consistent with the observed cold dark matter (CDM) relic density
Stable invisible weakly interacting massive particles (WIMPs) with proper mass and coupling strength can lead to a matter density that is consistent with the observed DM relic density in cosmic scale structure of the Universe [8]
Summary
The first evidence of dark matter (DM) was observed by Fritz Zwicky [1] in 1933. The existence of dark matter can be observed in the whole Universe, at the small galactic scale [2,3], the large scale of galaxy clusters [4,5], and the cosmological scale [6,7]. CCP, MSP, and TBTF, are called the small scale problem and they can be resolved if the CDM particles are self-interacting with a light mediator to give a large self-interacting cross section (SICS) [15]. A simple and elegant model with a self-interacting leptonic scalar dark matter (χ) and a light mediator (ζ) was recently proposed [24] to provide a CDM candidate and to solve the small scale problems of the Universe. We find the allowed parameter space that satisfies all constraints of (a) recent direct searches (b) indirect detection experiments, (c) the observed relic density, (d) effective number of neutrinos, and (e) the astrophysical observation of small-scale structure of Universe. Some useful formulas for Sommerfeld enhancement are presented in Appendix A
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