Shear and rotation in Chaplygin cosmology

TL;DR

This paper investigates how shear and rotation influence the spherical collapse model in generalized Chaplygin gas cosmologies, showing that these effects slow down structure formation and may address instability issues in unified dark matter models.

Contribution

It introduces the combined effect of shear and rotation into the spherical collapse model for gCg universes, demonstrating their role in moderating collapse and potentially solving instability problems.

Findings

Shear and rotation slow down the collapse process.

The results help address linear instability issues in unified dark matter models.

The effect varies with the parameter α of the gCg.

Abstract

We study the effect of shear and rotation on results previously obtained dealing with the application of the spherical collapse model (SCM) to generalized Chaplygin gas (gCg) dominated universes. The system is composed of baryons and gCg and the collapse is studied for different values of the parameter $\alpha$ of the gCg. We show that the joint effect of shear and rotation is that of slowing down the collapse with respect to the simple SCM. This result is of utmost importance for the so-called unified dark matter models, since the described slow down in the growth of density perturbation can solve one of the main problems of the quoted models, namely the instability described in previous papers [e.g., H. B. Sandvik {\it et al.}, Phys. Rev. D {\bf 69}, 123524 (2004)] at the linear perturbation level.