Testing the growth rate in homogeneous and inhomogeneous interacting vacuum models

Understand

In this work we consider a class of interacting vacuum corresponding to a generalised Chaplygin gas (gCg) cosmology.

• In particular we analyse two different scenarios at perturbation level for the same background interaction characterised by the parameter $\alpha$: (i) matter that follows geodesics, corresponding to homogeneous vacuum, and (ii) a covariant ansatz for vacuum density perturbations.
• In the latter case, we show that the vacuum perturbations are very tiny as compared to matter perturbations on sub-horizon scales.
• In spite of that, depending on the value of the Chaplygin gas parameter $\alpha$, vacuum perturbations suppress or enhance the matter growth rate as compared to the case (i).