The Frozen-Flow Approximation and the formation of cosmic structures

The issue of trying to reconstruct the initial conditions of the clustering process is a delicate one. Many attempts have been done in the past, with approximation methods such as the Zel'dovich one. However this method has a main drawback: it fails to describe the dynamics after shell-crossing. Therefore new methods have been developed, like the frozen-flow approximation, which overcomes the problems of caustic formation and can be implemented, following the idea behind the adhesion model, in order to obtain the so called viscid-flow approximation.