The structure and evolution of weakly self-interacting cold dark matter halos

The evolution of halos consisting of weakly self-interacting dark matter pa rticles is investigated using a new numerical Monte Carlo N-body method. Th e halos initially contain kinematically cold, dense r(-1) power-law cores. For interaction cross sections sigma* = sigma(wsi)/m(p) greater than or equ al to 10-100 cm(2) g(-1), weak self-interaction leads to the formation of i sothermal, constant-density cores within a Hubble time as a result of heat transfer into the cold inner regions. This core structure is in good agreem ent with the observations of dark matter rotation curves in dwarf galaxies. The isothermal core radii and core densities are a function of the halo sc ale radii and scale masses which depend on the cosmological model. Adopting the currently popular Lambda CDM model, the predicted core radii and core densities are in good agreement with the observations. For large interactio n cross sections, massive dark halos with scale radii r(s) greater than or equal to 1.3 x 10(4) cm(2) g(-1) (sigma*)(-1) kpc could experience core col lapse during their lifetime, leading to cores with singular isothermal dens ity profiles.