Reconciling the local void with the CMB

TL;DR

This paper demonstrates that an inhomogeneous void model, when using a physically motivated primordial spectrum, can simultaneously fit supernova, CMB, and local Hubble data without requiring dark energy, challenging standard cosmology assumptions.

Contribution

It introduces a modified primordial spectrum allowing inhomogeneous void models to fit multiple cosmological observations without dark energy.

Findings

Void models can fit supernova and CMB data with a suitable primordial spectrum.

The model satisfies baryon acoustic oscillation and nucleosynthesis constraints.

It challenges the necessity of dark energy in explaining cosmic acceleration.

Abstract

In the standard cosmological model, the dimming of distant Type Ia supernovae is explained by invoking the existence of repulsive `dark energy' which is causing the Hubble expansion to accelerate. However this may be an artifact of interpreting the data in an (oversimplified) homogeneous model universe. In the simplest inhomogeneous model which fits the SNe Ia Hubble diagram without dark energy, we are located close to the centre of a void modelled by a Lema\'itre-Tolman-Bondi metric. It has been claimed that such models cannot fit the CMB and other cosmological data. This is however based on the assumption of a scale-free spectrum for the primordial density perturbation. An alternative physically motivated form for the spectrum enables a good fit to both SNe Ia (Constitution/Union2) and CMB (WMAP 7-yr) data, and to the locally measured Hubble parameter. Constraints from baryon acoustic oscillations and primordial nucleosynthesis are also satisfied.