Study of corrections to the dust model via perturbation theory

Abstract

This work reports on the application of the Eulerian perturbation theory to a recently proposed model of cosmological structure formation by gravitational instability (astro-ph/0009414). Its physical meaning is discussed in detail and put in perspective of previous works. The model incorporates in a systematic fashion corrections to the popular dust model due to multistreaming and, more generally, the small-scale, virialized degrees of freedom. It features a time-dependent length scale L(t) estimated to be L/r0 ~ 0.1 (r0(t) is the nonlinear scale, at which the density variance =1). The model provides a new angle on the dust model and allows to overcome some of its limitations. Thus, the scale L(t) works as a physically meaningful short-distance cutoff for the divergences appearing in the perturbation expansion of the dust model when there is too much initial power on small scales. The model also incorporates the generation of vorticity by tidal forces; according to the perturbational result, the filtered vorticity for standard CDM initial conditions should be significant today only at scales below ~ 1 Mpc/h.