MeV Dark Matter in light of the Small Scale Crisis

Abstract

The small-scale crisis is one of the most outstanding puzzles in modern cosmology and astrophysics. It may imply a suppression of matter perturbation at small scale. In this work, by taking into account of the gravitational effects from the non-equilibrium production of DM, we propose a new mechanism, which can realize such desired suppression and alleviate the crisis within the framework of cold dark matter (DM) and simple inflation. Moreover, in this new mechanism, we establish a novel relation between the particle mass of DM, $m_{\chi }$, and the critical scale of suppression, $k_{\star }^{-1}$. As $k_{\star }^{-1}$ will be further constrained in future astrophysical observations, $m_{\chi }$ can be constrained accordingly with this relation. It thus provides a new method in complementary to other existing strategies of determining $m_{\chi }$. Furthermore, to illustrate our theoretical prediction, we consider a suppression at $k_{\star }^{-1}=1\text{kpc}$ that can partially alleviate the small-scale crisis, and obtain $m_{\chi }=2.2\text{MeV}$ for realizing such suppression. Then we plot the power spectrum of linear matter perturbation for this case, and illustrate a salient feature of the suppression that can serves a smoking-gun signature of this new mechanism in future observations.

5 pages, 5 figures