Comprehensive study of compact stars with dark matter

Abstract

We present a comprehensive study of compact stars admixed with non-self annihilating self-interacting fermionic dark matter, delineating the dependence on the nuclear equation of state by considering the two limiting parametrized equations of state for neutron star matter obtained by smoothly matching the low-density chiral effective theory and the high-density perturbative QCD. These two parametrizations are the limiting cases of a wide variety of smooth equations of state, i.e. the softest and stiffest possible one without a phase transition, that generate masses and radii compatible with 2M$_\odot$ observations and the tidal constraint from GW170817. With an exhaustive analysis of the possible stable mass-radius configurations, we determine the quantity of dark matter contained in stars with masses and radii compatible with the aforementioned astrophysical constraints. We find that for dark particle masses of a few tenths of GeV, the dark core collapses and no stable solutions are found for the two limiting ordinary matter equations of state. For lower masses, the dark matter fraction is limited to 10%, being at most 1% for masses ranging from 0.1 to 10 GeV for the limiting soft nuclear equation of state. For the limiting stiff nuclear equation of state, the dark matter fraction can reach values of more than 10%, but the dark particle mass is being constrained to 0.3 GeV and 10 GeV for the weak self-interacting case and has to be at least 5 GeV for the strong self-interacting one. For dark particle masses of less than 0.1 GeV, stable neutron star configurations should have less than 1% of self-interacting dark matter to be compatible with the constraint of the tidal deformability from GW170817 for the two limiting ordinary matter equations of state studied.