Current and future constraints on extended Bekenstein-type models for a varying fine-structure constant

TL;DR

This paper assesses current and future astrophysical and laboratory constraints on extended Bekenstein-type models for a varying fine-structure constant, highlighting how upcoming spectrographs can significantly tighten these bounds.

Contribution

It extends Bekenstein-type models to include couplings with dark matter and dark energy, and evaluates how future spectrographs will improve constraints on these models.

Findings

Current constraints limit couplings to parts per million.

Atomic clocks dominate existing bounds.

Future spectrographs can improve constraints by over an order of magnitude.

Abstract

There is a growing interest in astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant $\alpha$, as an optimal probe of new physics. The imminent arrival of the ESPRESSO spectrograph will soon enable significant gains in the precision and accuracy of these tests and widen the range of theoretical models that can be tightly constrained. Here we illustrate this by studying proposed extensions of the Bekenstein-type models for the evolution of $\alpha$ that allow different couplings of the scalar field to both dark matter and dark energy. We use a combination of current astrophysical and local laboratory data (from tests with atomic clocks) to show that these couplings are constrained to parts per million level, with the constraints being dominated by the atomic clocks. We also quantify the expected improvements from ESPRESSO and other future spectrographs, and briefly discuss possible observational strategies, showing that these facilities can improve current constraints by more than an order of magnitude.