Observing the thermalization of dark matter in neutron stars

TL;DR

This paper estimates the thermalization timescales of dark matter in neutron stars across various scenarios, crucial for understanding how dark matter affects neutron star observations and potential detection methods.

Contribution

It provides a comprehensive analysis of dark matter thermalization timescales considering different particle spins, target particles, interaction structures, and mediator masses.

Findings

Thermalization time depends on dark matter and mediator masses.

Efficient stellar capture and thermalization occur within the universe's age for certain parameters.

Regions identified where dark matter annihilation signals could be observed by infrared telescopes.

Abstract

A promising probe to unmask particle dark matter is to observe its effect on neutron stars, the prospects of which depend critically on whether captured dark matter thermalizes in a timely manner with the stellar core via repeated scattering with the Fermi-degenerate medium. In this work we estimate the timescales for thermalization for multiple scenarios. These include: (a) spin-0 and spin-$\frac{1}{2}$ dark matter, (b) scattering on non-relativistic neutron and relativistic electron targets accounting for the respective kinematics, (c) interactions via a range of Lorentz-invariant structures, (d) mediators both heavy and light in comparison to the typical transfer momenta in the problem. We discuss the analytic behavior of the thermalization time as a function of the dark matter and mediator masses, and the stellar temperature. Finally, we identify parametric ranges where both stellar capture is efficient and thermalization occurs within the age of the universe. For dark matter that can annihilate in the core, these regions indicate parametric ranges that can be probed by upcoming infrared telescopes observing cold neutron stars.