Early supersymmetric cold dark matter substructure

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  • 9 March 2006
Abstract
Earth-mass dark matter microhalos may be the first objects to collapse and virialize in the early universe. Their ability to survive the hierarchical clustering process as substructure in the larger halos that form subsequently has implications for direct and indirect dark matter detection experiments. We present here the large N-body simulation of early substructure in a supersymmetric cold dark matter (SUSY-CDM) scenario characterized by an exponential cutoff in the matter power spectrum at M_c=10^{-6} Msun. The simulation resolves a 0.014 Msun parent SUSY halo at z=75 with 12 million particles within its virial radius. On these scales the effective index of the power spectrum approaches -3, a range of mass scales collapse almost simultaneously, and the formation history of the early SUSY host appears very different from that of a low-redshift massive halo. Compared to a z=0 galaxy cluster with similar concentration parameter, substructure within our SUSY host is less evident both in phase-space and in physical space, and it is less resistant against tidal stripping and disruption. As the scale factor of the universe increases by a factor of 1.3, we find that between 20 and 40 percent of well-resolved SUSY substructure is destroyed, compared to only about 1 percent in the low-redshift cluster. Despite the lower contrast and higher disruption probability, SUSY substructure is just as abundant as in z=0 galaxy clusters, i.e. the substructure normalized mass and circular velocity functions are very similar. The dark matter self-annihilation gamma-ray signal from resolved sub-microhalos is comparable to the spherically-averaged SUSY host signal, and should be included in estimates of the cosmological extragalactic gamma-ray background.(ABRIDGED)

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