Backreaction on the luminosity-redshift relation from gauge invariant light-cone averaging

TL;DR

This paper investigates how gauge-invariant light-cone averaging and inhomogeneities affect the luminosity-redshift relation, revealing that backreaction effects are significant but insufficient to explain dark energy without higher-order calculations.

Contribution

It introduces a gauge-invariant light-cone averaging method and analyzes the backreaction effects from primordial inhomogeneities on cosmological observations.

Findings

Backreaction effects are larger than expected from primordial inhomogeneities.

Linear analysis shows backreaction cannot fully explain dark energy effects.

Higher-order and non-linear effects are needed for conclusive results.

Abstract

Using a recently proposed gauge invariant formulation of light-cone averaging, together with adapted "geodesic light-cone" coordinates, we show how an "induced backreaction" effect emerges, in general, from correlated fluctuations in the luminosity distance and covariant integration measure. Considering a realistic stochastic spectrum of inhomogeneities of primordial (inflationary) origin we find that both the induced backreaction on the luminosity-redshift relation and the dispersion are larger than naively expected. On the other hand the former, at least to leading order and in the linear perturbative regime, cannot account by itself for the observed effects of dark energy at large-redshifts. A full second-order calculation, or even better a reliable estimate of contributions from the non-linear regime, appears to be necessary before firm conclusions on the correct interpretation of the data can be drawn.