A glitch in gravity: cosmic Lorentz-violation from fiery Big Bang to glacial heat death

TL;DR

This paper explores a cosmological model where gravity's strength varies across different scales, revealing a potential violation of general relativity at the Big Bang and suggesting a scale-dependent recovery of symmetries.

Contribution

It introduces a single-parameter extension to the standard model with scale-dependent gravity, supported by observational data indicating a weaker superhorizon gravity and evidence of a stronger glitch during Big Bang nucleosynthesis.

Findings

Weaker superhorizon gravity improves Hubble and clustering tensions.

Evidence of a stronger gravity glitch during Big Bang nucleosynthesis.

Gradual recovery of general relativity symmetries over cosmic time.

Abstract

One regime where we might see departures from general relativity is at the largest accessible scales, with a natural choice in cosmology being the cosmological horizon (or Hubble) scale. We investigate a single-parameter extension to the standard cosmological model with a different strength of gravity above and below this scale -- a "cosmic glitch" in gravity. Cosmic microwave background observations, and Baryonic Acoustic Oscillations (including the recent DESI Y1) favour weaker superhorizon gravity, at nearly a percent (or 2$\sigma$ level), easing both the Hubble and clustering tensions with other cosmological data. This compounds evidence for an even stronger glitch during Big Bang nucleosynthesis (from helium abundance observations), suggesting that symmetries of general relativity are maximally violated at the Big Bang, but gradually recovered as we approach the present-day cosmological de Sitter scale, associated with the observed dark energy.