  We explore the effects of small scale structure on the formation and
equilibrium of dark matter halos in a universe dominated by vacuum energy. We
present the results of a suite of four N-body simulations, two with a LCDM
initial power spectrum and two with WDM-like spectra that suppress the early
formation of small structures. All simulations are run into to far future when
the universe is 64Gyr/h old, long enough for halos to essentially reach
dynamical equilibrium. We quantify the importance of hierarchical merging on
the halo mass accretion history, the substructure population, and the
equilibrium density profile. We modify the mass accretion history function of
Wechsler et al. (2002) by introducing a parameter, \gamma, that controls the
rate of mass accretion, dln(M) / dln(a) ~ a^(-\gamma), and find that this form
characterizes both hierarchical and monolithic formation. Subhalo decay rates
are exponential in time with a much shorter time scale for WDM halos. At the
end of the simulations, we find truncated Hernquist density profiles for halos
in both the CDM and WDM cosmologies. There is a systematic shift to lower
concentration for WDM halos, but both cosmologies lie on the same locus
relating concentration and formation epoch. Because the form of the density
profile remains unchanged, our results indicate that the equilibrium halo
density profile is set independently of the halo formation process.
