The variation of the fine-structure constant from disformal couplings

TL;DR

This paper investigates how disformal couplings between a scalar field and electromagnetic fields can explain variations in the fine-structure constant, consistent with current astrophysical and laboratory constraints, and discusses future observational prospects.

Contribution

It introduces a model where disformal couplings modify alpha and explores its implications, including explaining observed variations and constraining parameters with data.

Findings

Disformal couplings can account for observed variations in alpha.

Models are consistent with astrophysical, cosmological, and laboratory constraints.

Future high-precision measurements will further test these models.

Abstract

We study a theory in which the electromagnetic field is disformally coupled to a scalar field, in addition to a usual non-minimal electromagnetic coupling. We show that disformal couplings modify the expression for the fine-structure constant, alpha. As a result, the theory we consider can explain the non-zero reported variation in the evolution of alpha by purely considering disformal couplings. We also find that if matter and photons are coupled in the same way to the scalar field, disformal couplings itself do not lead to a variation of the fine-structure constant. A number of scenarios are discussed consistent with the current astrophysical, geochemical, laboratory and the cosmic microwave background radiation constraints on the cosmological evolution of alpha. The models presented are also consistent with the current type Ia supernovae constraints on the effective dark energy equation of state. We find that the Oklo bound in particular puts strong constraints on the model parameters. From our numerical results, we find that the introduction of a non-minimal electromagnetic coupling enhances the cosmological variation in alpha. Better constrained data is expected to be reported by ALMA and with the forthcoming generation of high-resolution ultra-stable spectrographs such as PEPSI, ESPRESSO, and ELT-HIRES. Furthermore, an expected increase in the sensitivity of molecular and nuclear clocks will put a more stringent constraint on current laboratory measurements.