Hiding dark energy transitions at low redshift

TL;DR

This paper demonstrates that significant fluctuations in dark energy at ultra-low redshifts can be hidden from current and future measurements, challenging assumptions about the uniformity of dark energy's influence on cosmic expansion.

Contribution

It introduces scalar field models with sharp potential features that can produce large local fluctuations in dark energy without conflicting with observational data.

Findings

Dark energy fluctuations at z<0.02 can mimic local Hubble rate transitions.

Scalar field models with sharp potential features can produce large equation of state variations.

Such fluctuations can evade detection by high-precision, high-redshift measurements.

Abstract

We show that it is both observationally allowable and theoretically possible to have large fluctuations in the dark energy equation of state as long as they occur at ultra-low redshifts z<0.02. These fluctuations would masquerade as a local transition in the Hubble rate of a few percent or less and escape even future, high precision, high redshift measurements of the expansion history and structure. Scalar field models that exhibit this behavior have a sharp feature in the potential that the field traverses within a fraction of an e-fold of the present. The equation of state parameter can become arbitrarily large if a sharp dip or bump in the potential causes the kinetic and potential energy of the field to both be large and have opposite sign. While canonical scalar field models can decrease the expansion rate at low redshift, increasing the local expansion rate requires a non-canonical kinetic term for the scalar field.