Coupling quintessence kinetics to electromagnetism

TL;DR

This paper introduces a novel model where quintessence couples to electromagnetism through its kinetic term, leading to a time variation of the fine-structure constant, tested against diverse observational data.

Contribution

It generalizes the gauge kinetic function dependence on the scalar field and analyzes the resulting alpha variation within a disformal coupling framework.

Findings

Alpha variation evolves differently across cosmological eras.

Atomic clock data provides the tightest bounds on the interaction.

Quasar observations are consistent with weak equivalence principle tests.

Abstract

We propose a general model where quintessence couples to electromagnetism via its kinetic term. This novelty generalizes the linear dependence of the gauge kinetic function on $\phi$, commonly adopted in the literature. The interaction naturally induces a time variation of the fine-structure constant that can be formulated within a disformally coupled framework, akin to a Gordon metric. Through a suitable parametrization of the scalar field and the coupling function, we test the model against observations sensitive to the variation of $\alpha$. We undertake a Bayesian analysis to infer the free parameters with data from Earth based, astrophysical and early Universe experiments. We find that the evolution of $\alpha$ is specific to each cosmological era and slows down at late times when dark energy accelerates the Universe. While the most stringent bound on the interaction is obtained from atomic clocks measurements, the quasars provide a constraint consistent with weak equivalence principle tests. This promising model is to be further tested with upcoming and more precise astrophysical measurements, such as those of the ESPRESSO spectrograph.