Annihilating the Cold Dark Matter Cusp Crisis

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Abstract
Structure formation with cold dark matter (CDM) predicts halos with a central density cusp, which is observationally disfavored. If CDM particles have an annihilation cross section ~ 10^{-28} (m/GeV) cm^2, then annihilations in the dense, central parts of halos will soften the cusps. The predicted softened halo core densities depend critically upon the velocity dependence of the annihilation cross section. We show that from galactic satellites to clusters of galaxies, the halos all have nearly the same core density: rho_core ~ 0.02 M_sun/pc^3 = 0.8 GeV/cm^3. This remarkable fact implicates s-wave annihilation. We discuss the constraints on models for annihilating CDM, which point to a candidate beyond those currently favored.

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