Vacuum energy as dark matter

TL;DR

This paper investigates how vacuum energy from massive quantum fields in an expanding universe can mimic dark matter, potentially explaining dark matter's properties through quantum vacuum effects.

Contribution

It introduces a conserved renormalized vacuum energy-momentum tensor and demonstrates conditions where vacuum energy behaves like nonrelativistic matter in cosmology.

Findings

Vacuum energy density can scale as nonrelativistic matter at late times.

Vacuum energy can be compatible with current dark matter abundance limits.

Density perturbations in vacuum energy can grow similarly to cold dark matter.

Abstract

We consider the vacuum energy of massive quantum fields in an expanding universe. We define a conserved renormalized energy-momentum tensor by means of a comoving cutoff regularization. Using exact solutions for de Sitter space-time, we show that in a certain range of mass and renormalization scales there is a contribution to the vacuum energy density that scales as nonrelativistic matter and that such a contribution becomes dominant at late times. By means of the WKB approximation, we find that these results can be extended to arbitrary Robertson-Walker geometries. We study the range of parameters in which the vacuum energy density would be compatible with current limits on dark matter abundance. Finally, by calculating the vacuum energy in a perturbed Robertson-Walker background, we obtain the speed of sound of density perturbations and show that the vacuum energy density contrast can grow on sub-Hubble scales as in standard cold dark matter scenarios.