Back-Reaction of Super-Hubble Cosmological Perturbations Beyond Perturbation Theory

TL;DR

This paper investigates how super-Hubble cosmological fluctuations influence the local Hubble rate, revealing that infrared fluctuations can dynamically relax a large cosmological constant without relying on perturbative methods.

Contribution

It demonstrates, beyond perturbation theory, that infrared fluctuations cause a negative correction to the local expansion rate, supporting a mechanism for cosmological constant relaxation.

Findings

Infrared fluctuations decrease the local Hubble rate over time.

The effect mimics a decreasing cosmological constant.

Analysis does not depend on perturbative amplitude expansion.

Abstract

We discuss the effect of super-Hubble cosmological fluctuations on the locally measured Hubble expansion rate. We consider a large bare cosmological constant in the early universe in the presence of scalar field matter (the dominant matter component), which would lead to a scale-invariant primordial spectrum of cosmological fluctuations. Using the leading order gradient expansion we show that the expansion rate measured by a (secondary) clock field which is not comoving with the dominant matter component obtains a negative contribution from infrared fluctuations, a contribution whose absolute value increases in time. This is the same effect which a decreasing cosmological constant would produce. This supports the conclusion that infrared fluctuations lead to a dynamical relaxation of the cosmological constant. Our analysis does not make use of any perturbative expansion in the amplitude of the inhomogeneities.