Avoiding the dark energy coincidence problem with a cosmic vector

TL;DR

This paper explores vector field theories as natural candidates for dark energy, demonstrating their compatibility with observations and showing how electromagnetic fields could explain the cosmological constant without new physics.

Contribution

It introduces vector theories without potential terms as dark energy models, linking electromagnetic fields to the cosmological constant within standard inflationary cosmology.

Findings

One model fits supernova data well.

Electromagnetic fields can generate an effective cosmological constant.

Models are compatible with local gravity tests.

Abstract

We show that vector theories on cosmological scales are excellent candidates for dark energy. We consider two different examples, both are theories with no dimensional parameters nor potential terms, with natural initial conditions in the early universe and the same number of free parameters as LCDM. The first one exhibits scaling behaviour during radiation and a strong phantom phase today, ending in a "big-freeze" singularity. This model provides the best fit to date for the SNIa Gold dataset. The second theory we consider is standard electromagnetism. We show that a temporal electromagnetic field on cosmological scales generates an effective cosmological constant and that primordial electromagnetic quantum fluctuations produced during electroweak scale inflation could naturally explain, not only the presence of this field, but also the measured value of the dark energy density. The theory is compatible with all the local gravity tests, and is free from classical or quantum instabilities. Thus, not only the true nature of dark energy could be established without resorting to new physics, but also the value of the cosmological constant would find a natural explanation in the context of standard inflationary cosmology.