Rendering Dark Energy Void

TL;DR

This paper explores how inhomogeneous void models within general relativity can mimic dark energy effects, analyzing their parameters, observational constraints, and the potential to distinguish them from standard cosmology.

Contribution

It introduces a simple parameterization of voids that can replicate standard cosmological distances and discusses how Hubble-rate data can help differentiate these models from the concordance model.

Findings

Void models can reproduce distance measurements with arbitrary accuracy.

Current supernova data can constrain the size of a void independently of its shape.

Local peculiar velocities limit the constraints on the sharpness of the density profile.

Abstract

Dark energy observations may be explained within general relativity using an inhomogeneous Hubble-scale depression in the matter density and accompanying curvature, which evolves naturally out of an Einstein-de Sitter (EdS) model. We present a simple parameterization of a void which can reproduce concordance model distances to arbitrary accuracy, but can parameterize away from this to give a smooth density profile everywhere. We show how the Hubble constant is not just a nuisance parameter in inhomogeneous models because it affects the shape of the distance-redshift relation. Independent Hubble-rate data from age estimates can in principle serve to break the degeneracy between concordance and void models, but the data is not yet able to achieve this. Using the latest Constitution supernova dataset we show that robust limits can be placed on the size of a void which is roughly independent of its shape. However, the sharpness of the profile at the origin cannot be well constrained due to supernova being dominated by peculiar velocities in the local Universe. We illustrate our results using some recently proposed diagnostics for the Friedmann models.