Realistic neutron star constraints on bosonic asymmetric dark matter

TL;DR

This paper reevaluates constraints on bosonic asymmetric dark matter from neutron star observations, emphasizing the role of self-interactions and co-annihilation, and finds that most realistic models are not excluded.

Contribution

It demonstrates that self-interactions and co-annihilation significantly weaken previous neutron star constraints on bosonic asymmetric dark matter.

Findings

Self-interactions prevent black hole formation in neutron stars.

Co-annihilation with nucleons reduces dark matter accumulation.

Most realistic bosonic asymmetric dark matter models are not excluded.

Abstract

It has been argued that the existence of old neutron stars excludes the possibility of non-annihilating light bosonic dark matter, such as that arising in asymmetric dark matter scenarios. If non-annihilating dark matter is captured by neutron stars, the density will eventually become sufficient for black hole formation. However, the dynamics of collapse is highly sensitive to dark-matter self-interactions. Repulsive self-interactions, even if extremely weak, can prevent black hole formation. We argue that self-interactions will necessarily be present, and estimate their strength in representative models. We also consider co-annihilation of dark matter with nucleons, which arises naturally in many asymmetric dark matter models, and which again acts to prevent black hole formation. We demonstrate how the excluded region of the dark-matter parameter space shrinks as the strength of such interactions is increased, and conclude that neutron star observations do not exclude most realistic bosonic asymmetric dark matter models.