A Frozen-Flow Approximation to the Evolution of Large-Scale Structures in the Universe

The study proposes a new approximation to the evolution of large-scale structures in the Universe which is based on neglecting the role of particle inertia compared to the damping implied by the Hubble drag. This assumption makes it possible to prevent the occurrence of orbit crossing, which represents the main drawback of the Zel'dovich approximation. Owing to this property, an approximate description of the Eulerian density field at later times and/or on smaller scales compared to the classical Zel'dovich algorithm is obtained. The approximation scheme is applied to follow the evolution of structures within the standard CDM model, where it gives a fairly accurate representation of the density pattern from a resolution scale of about 500 km/s, while the two-point correlation function fits the true nonlinear result quite well, even on small scales. This method offers a strong reduction in the computational time, without a significant loss of accuracy.