The isotropy of Hubble expansion in the early and late Universe

TL;DR

This study tests the isotropy of the universe's expansion across different epochs using multiple cosmological probes, finding no significant anisotropy and setting tight upper limits on possible directional variations.

Contribution

It constructs comprehensive full-sky maps of expansion rate variations combining supernovae, galaxy data, and CMB, providing the first such combined analysis with stringent anisotropy constraints.

Findings

No detected anisotropy in Hubble expansion across probes

Upper limits on anisotropy are below 1% at 99% confidence

An anomaly in fundamental plane residuals likely due to dataset systematics

Abstract

We test the isotropy of Hubble expansion by combining several probes for the first time, constructing full-sky maps of expansion rate variation using Type Ia supernovae, fundamental plane galaxies, and CMB temperature fluctuations. We find no hint of anisotropy or correlation between early- and late-Universe expansion across all systematic models. The 99% confidence upper limits on expansion rate anisotropy are 0.39% for low-redshift supernovae, 0.95% for high-redshift CMB, and 0.37% when combined at a 60-degree smoothing scale. A significant anomaly in the fundamental plane residual map may reflect systematics in the current DESI dataset, as evidenced by the absence of cross-correlation with other tracers and its correlation with spatial density variations.