Inhomogeneous and interacting vacuum energy

TL;DR

This paper develops a general framework for inhomogeneous, interacting vacuum energy in cosmology, exploring its implications for dark energy models and observable signatures like CMB anisotropies and matter power spectra.

Contribution

It introduces a comprehensive set of equations for spacetime-dependent vacuum energy, including perturbations, and demonstrates how various models can be distinguished observationally.

Findings

Different interaction models affect dark energy perturbations and sound speed.

Cosmic microwave background anisotropies vary with interaction models.

Matter power spectrum is sensitive to vacuum energy inhomogeneity.

Abstract

Vacuum energy is a simple model for dark energy driving an accelerated expansion of the universe. If the vacuum energy is inhomogeneous in spacetime then it must be interacting. We present the general equations for a spacetime-dependent vacuum energy in cosmology, including inhomogeneous perturbations. We show how any dark energy cosmology can be described by an interacting vacuum+matter. Different models for the interaction can lead to different behaviour (e.g., sound speed for dark energy perturbations) and hence could be distinguished by cosmological observations. As an example we present the cosmic microwave microwave background anisotropies and the matter power spectrum for two different versions of a generalised Chaplygin gas cosmology.