Published online by Cambridge University Press: 19 May 2006
N-body simulations find a universal structure for the halos whichresult from the nonlinear growth of Gaussian-random-noise densityfluctuations in the CDM universe. This talk summarized our attempts toderive and explain this universal structure by analyticalapproximation and simplified models. As an example, we show here thata 1D spherical infall model involving a fluid approximation derivedfrom the Boltzmann equation can explain not only the halo density profilebut its phase-space density profile, as well.