Annihilating Cold Dark Matter

Structure formation with cold dark matter (CDM) predicts halos with a central density cusp, which are observationally disfavored. If CDM particles have an annihilation cross section σv~10^-29\(m/GeV\) cm², then annihilations will soften the cusps. We discuss plausible scenarios for avoiding the early Universe annihilation catastrophe that could result from such a large cross section. The predicted scaling of core density with halo mass depends upon the velocity dependence of σv, and s-wave annihilation leads to a core density nearly independent of halo mass, which seems consistent with observations.