Dark-Matter Decays and Self-Gravitating Halos

TL;DR

This paper investigates how decaying dark matter particles with small velocity kicks influence the structure and evolution of dark matter halos, using simulations and observational constraints to limit decay parameters.

Contribution

It introduces a detailed simulation study of dark matter decay effects on halos and constrains decay parameters using observational data.

Findings

Decays with kick velocities >100 km/s and decay times < a few times the universe's age are ruled out.

Dark matter decays can disrupt low-velocity halos and heat larger halos.

The decay parameters significantly affect the halo mass-concentration relation and mass function.

Abstract

We consider models in which a dark-matter particle decays to a slightly less massive daughter particle and a noninteracting massless particle. The decay gives the daughter particle a small velocity kick. Self-gravitating dark-matter halos that have a virial velocity smaller than this velocity kick may be disrupted by these particle decays, while those with larger virial velocities will be heated. We use numerical simulations to follow the detailed evolution of the total mass and density profile of self-gravitating systems composed of particles that undergo such velocity kicks as a function of the kick speed (relative to the virial velocity) and the decay time (relative to the dynamical time). We show how these decays will affect the halo mass-concentration relation and mass function. Using measurements of the halo mass-concentration relation and galaxy-cluster mass function to constrain the lifetime--kick-velocity parameter space for decaying dark matter, we find roughly that the observations rule out the combination of kick velocities greater than 100 km/s and decay times less than a few times the age of the Universe.