Condensed dark matter with a Yukawa interaction

In this talk, we explore 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 will proceed to discuss the BCS phase in detail 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 valid in both the non-relativistic and relativistic regimes. Numerical solutions to the set of gap equations are presented, in particular when the mediator mass is smaller and larger than the DM mass, at instances where a phase transition from BEC-crossover-BCS can be observed. We shall conclude with a few applications of the above formalism. Specifically, description of DM equation of state and their astrophysical implications for asymmetric DM halos, and gravo-thermal catastrophe.

Based on: Phys.Rev.D 106 (2022) 11, 116003 (ArXiV: 2207.06928)