Mapping the allowed parameter space for decaying dark matter models

TL;DR

This paper explores constraints on decaying dark matter models with two WIMP species, focusing on how decay affects dark matter halos and deriving bounds on decay parameters from observational data.

Contribution

It maps the allowed parameter space for decaying dark matter models using observational constraints without relying on N-body simulations for certain parameters.

Findings

Galaxy cluster mass function constrains decay time to >40 Gyr for high velocities.

Halo properties can limit decay parameters without simulations for some cases.

Precise constraints for lower velocities require N-body simulations.

Abstract

I consider constraints on a phenomenological decaying-dark-matter model, in which two weakly-interacting massive particle (WIMP) species have a small mass splitting, and in which the heavier particle decays to the lighter particle and a massless particle on cosmological timescales. The decay parameter space is parameterized by $v_k$, the speed of the lighter particle in the center-of-mass frame of the heavier particle prior to decay, and the decay time $\tau$. Since I consider the case in which dark-matter halos have formed before there has been significant decay, I focus on the effects of decay in already-formed halos. I show that the $v_k-\tau$ parameter space may be constrained by observed properties of dark-matter halos. I highlight which set of observations is likely to yield the cleanest constraints on $v_k-\tau$ parameter space, and calculate the constraints in those cases in which the effect of decay on the observables can be calculated without N-body simulations of decaying dark matter. I show that for $v_k \gtrsim 5\times 10^3$ km s$^{-1}$, the z=0 galaxy cluster mass function and halo mass-concentration relation constrain $\tau \gtrsim$ 40 Gyr, and that precise constraints on $\tau$ for smaller $v_k$ will require N-body simulations.