Narrow Results

The nature of cosmological dark matter finds its explanation in physics beyond the Standard Model of elementary particles. The landscape of dark matter candidates contains a wide variety of species, either elusive or hardly detectable in direct experimental searches. Even in case, when such searches are possible the interpretation of their results implies additional sources of information, which provide indirect effects of dark matter. Some nontrivial probes for the nature of the dark matter are presented in the present issue.

The dark matter admixed neutron stars (DANSs) are studied using the two-fluid TOV equations separately, in which the normal matter (NM) and dark matter (DM) are simulated by the relativistic mean field theory and self-interacting fermionic model, respectively. A universal relationship $M_D^{max}=(0.269\frac{m_f}{m_I}+0.627){(\frac{1\mathrm{\text{GeV}}}{m_f})}^2{\mathrm{\text{M}}}_{\odot }$ is suggested, where $M_D^{max}$ is the maximum mass of DM existing in DANSs, $m_f$ is the particle mass of DM ranging from 5GeV to 1TeV, $m_I$ is the interaction mass scale with the value 300GeV (0.1GeV) for weak (strong) interaction DM model. This simple formula connects directly the microcosmic nature of DM particle with its macrocosmic mass existing in DANSs. Meanwhile, such a formula exhibits that the existence of NM has little effect on $M_D^{max}$. It is found that the ratio of radius of DM in DANSs over $M_D^{max}$ is a constant with the value about 12$\frac{\mathrm{\text{km}}}{{\mathrm{\text{M}}}_{\odot }}$ (7$\frac{\mathrm{\text{km}}}{{\mathrm{\text{M}}}_{\odot }}$) for weak (strong) interaction DM cases. According to the calculated results, only for the strong interaction DM cases with $m_f=5$ to $10$GeV and central energy density ${𝜀}_D>10^3$MeV/fm³, DM has obvious effect on the mass of compact star. Compared with the energy density of DM in the Milky Way galaxy, $\sim 10^{-36}$MeV/fm³, the existence of DM might hardly affect the mass of compact stars in the Milky Way galaxy.