The kSZ effect as a test of general radial inhomogeneity in LTB cosmology

TL;DR

This paper investigates whether general LTB models with variable bang time can explain cosmic acceleration without dark energy, finding that observational constraints strongly limit their viability.

Contribution

It demonstrates that relaxing the bang time assumption in LTB models does not reconcile them with key cosmological observations, challenging their role as dark energy alternatives.

Findings

Variable bang time models cannot fit all key observations simultaneously.

Observational constraints effectively rule out simple LTB models as dark energy substitutes.

The set of cosmological data strongly constrains large-scale inhomogeneity models.

Abstract

The apparent accelerating expansion of the Universe, determined from observations of distant supernovae, and often taken to imply the existence of dark energy, may alternatively be explained by the effects of a giant underdense void if we relax the assumption of homogeneity on large scales. Recent studies have made use of the spherically-symmetric, radially-inhomogeneous Lemaitre-Tolman-Bondi (LTB) models to derive strong constraints on this scenario, particularly from observations of the kinematic Sunyaev-Zel'dovich (kSZ) effect which is sensitive to large scale inhomogeneity. However, most of these previous studies explicitly set the LTB 'bang time' function to be constant, neglecting an important freedom of the general solutions. Here we examine these models in full generality by relaxing this assumption. We find that although the extra freedom allowed by varying the bang time is sufficient to account for some observables individually, it is not enough to simultaneously explain the supernovae observations, the small-angle CMB, the local Hubble rate, and the kSZ effect. This set of observables is strongly constraining, and effectively rules out simple LTB models as an explanation of dark energy.