Mapping the allowed parameter space for decaying dark matter models

Abstract

I consider constraints on a phenomenological decaying dark matter model, in which two weakly interacting massive particle species have a small mass splitting, and in which the heavier particle decays to the lighter particle and a massless particle on cosmological time scales. The decay parameter space is parametrized 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 τ. 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 on already formed halos. I show that the v_k-τ 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-τ 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 ≳ 5×10^3  km s^(-1), the z=0 galaxy cluster mass function and halo mass-concentration relation constrain τ ≳ 40  Gyr, and that precise constraints on τ for smaller v_k will require N-body simulations.

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