Constraining Variations in the Fine Structure Constant in the presence of Early Dark Energy

TL;DR

This paper investigates how early dark energy could cause variations in the fine structure constant and uses cosmological data to constrain such variations, finding no significant change at recombination and discussing future measurement prospects.

Contribution

It provides the first comprehensive cosmological constraints on variations of the fine structure constant due to early dark energy with linear coupling, and compares these with local tests.

Findings

No variation of alpha at recombination within 95% confidence

Current cosmological constraints on coupling are weaker than local tests

Future missions could improve sensitivity to coupling strength

Abstract

We discuss present and future cosmological constraints on variations of the fine structure constant $\alpha$ induced by an early dark energy component having the simplest allowed (linear) coupling to electromagnetism. We find that current cosmological data show no variation of the fine structure constant at recombination respect to the present-day value, with $\alpha$ / $\alpha_0$ = 0.975 \pm 0.020 at 95 % c.l., constraining the energy density in early dark energy to $\Omega_e$ < 0.060 at 95 % c.l.. Moreover, we consider constraints on the parameter quantifying the strength of the coupling by the scalar field. We find that current cosmological constraints on the coupling are about 20 times weaker than those obtainable locally (which come from Equivalence Principle tests). However forthcoming or future missions, such as Planck Surveyor and CMBPol, can match and possibly even surpass the sensitivity of current local tests.