  An inside-out model for the formation of haloes in a hierarchical clustering
scenario is studied. The method combines the picture of the spherical infall
model and a modification of the extended Press-Schechter theory. The mass
accretion rate of a halo is defined to be the rate of its mass increase due to
minor mergers. The accreted mass is deposited at the outer shells without
changing the density profile of the halo inside its current virial radius. We
applied the method to a flat $\Lambda CDM$ Universe. The resulting density
profiles are compared to analytical models proposed in the literature, and a
very good agreement is found. A trend is found of the inner density profile
becoming steeper for larger halo mass, that also results from recent N-body
simulations. Additionally, present-day concentrations as well as their time
evolution are derived and it is shown that they reproduce the results of large
cosmological N-body simulations.
