Can decaying modes save void models for acceleration?

TL;DR

This paper demonstrates that models with significant decaying modes cannot explain cosmic observations without conflicting with CMB spectral distortion constraints, thereby supporting the standard homogeneous cosmology.

Contribution

It shows that including decaying modes in void models is inconsistent with CMB spectral distortion limits, closing a loophole against inhomogeneous cosmologies.

Findings

Decaying modes are incompatible with observed CMB spectral distortions.

Void models with decaying modes are ruled out by current observations.

Supports the standard homogeneous universe model.

Abstract

The unexpected dimness of Type Ia supernovae (SNe), apparently due to accelerated expansion driven by some form of dark energy or modified gravity, has led to attempts to explain the observations using only general relativity with baryonic and cold dark matter, but by dropping the standard assumption of homogeneity on Hubble scales. In particular, the SN data can be explained if we live near the centre of a Hubble-scale void. However, such void models have been shown to be inconsistent with various observations, assuming the void consists of a pure growing mode. Here it is shown that models with significant decaying mode contribution today can be ruled out on the basis of the expected cosmic microwave background spectral distortion. This essentially closes one of the very few remaining loopholes in attempts to rule out void models, and strengthens the evidence for Hubble-scale homogeneity.