Condensed dark matter with a Yukawa interaction

We explore the possible phases of a condensed dark matter (DM) candidate taken to be in the form of a fermion with a Yukawa coupling to a scalar particle, at zero temperature but at finite density. This theory essentially depends on only four parameters, the Yukawa coupling, the fermion mass, the scalar mediator mass, and the DM density. At low-fermion densities we delimit the Bardeen-Cooper-Schrieffer (BCS), Bose-Einstein condensate (BEC), and crossover phases as a function of model parameters using the notion of scattering length. We further study the BCS phase by consistently including emergent effects such as the scalar-density condensate and superfluid gaps. Within the mean-field approximation, we derive the consistent set of gap equations, retaining their momentum dependence, and valid in both the nonrelativistic and relativistic regimes. We present numerical solutions to the set of gap equations, in particular when the mediator mass is smaller and larger than the DM mass. Finally, we discuss the equation of state and possible astrophysical implications for asymmetric DM.

Automated summary

In this paper, we explore the different phases of a condensed dark matter candidate, which is a fermion with a Yukawa coupling to a scalar particle. We investigate the BCS, BEC, and crossover phases as a function of model parameters and consider emergent effects such as scalar-density condensate and superfluid gaps. By numerically solving the consistent set of gap equations, valid in both the nonrelativistic and relativistic regimes, we discuss the equation of state and possible astrophysical implications for asymmetric dark matter.