Asymmetric condensed dark matter

TL;DR

This paper investigates a bosonic asymmetric dark matter model where a Bose-Einstein condensate forms in the early universe, requiring light particles and weak interactions, with implications for cosmology and relic densities.

Contribution

It introduces a thermal field theory analysis of asymmetric bosonic dark matter forming a condensate, highlighting conditions for its survival and cosmological constraints.

Findings

Dark matter particles must be lighter than a few tens of eV.

Condensate formation occurs in thermal equilibrium in the early universe.

Decoupling must happen at or above the QCD phase transition temperature.

Abstract

We explore the viability of a boson dark matter candidate with an asymmetry between the number densities of particles and antiparticles. A simple thermal field theory analysis confirms that, under certain general conditions, this component would develop a Bose-Einstein condensate in the early universe that, for appropriate model parameters, could survive the ensuing cosmological evolution until now. The condensation of a dark matter component in equilibrium with the thermal plasma is a relativistic process, hence the amount of matter dictated by the charge asymmetry is complemented by a hot relic density frozen out at the time of decoupling. Contrary to the case of ordinary WIMPs, dark matter particles in a condensate must be lighter than a few tens of eV so that the density from thermal relics is not too large. Big-Bang nucleosynthesis constrains the temperature of decoupling to the scale of the QCD phase transition or above. This requires large dark matter-to-photon ratios and very weak interactions with standard model particles.