Dark energy and Equivalence Principle constraints from astrophysical tests of the stability of the fine-structure constant

TL;DR

Astrophysical and local tests of fundamental constants and dark energy models tightly constrain their interactions, with implications for the equivalence principle and future observational prospects.

Contribution

This paper links astrophysical measurements of the fine-structure constant to dark energy models, deriving new bounds on their coupling and equivalence principle violations.

Findings

Current data constrains the coupling parameter $$ and dark energy equation of state.

Indirect bounds on the Ef6tvf6s parameter $$ are stronger than direct measurements.

Future spectrographs will improve constraints significantly.

Abstract

Astrophysical tests of the stability of fundamental couplings, such as the fine-structure constant $\alpha$, are becoming an increasingly powerful probe of new physics. Here we discuss how these measurements, combined with local atomic clock tests and Type Ia supernova and Hubble parameter data, constrain the simplest class of dynamical dark energy models where the same degree of freedom is assumed to provide both the dark energy and (through a dimensionless coupling, $\zeta$, to the electromagnetic sector) the $\alpha$ variation. Specifically, current data tightly constrains a combination of $\zeta$ and the present dark energy equation of state $w_0$. Moreover, in these models the new degree of freedom inevitably couples to nucleons (through the $\alpha$ dependence of their masses) and leads to violations of the Weak Equivalence Principle. We obtain indirect bounds on the E\"otv\"os parameter $\eta$ that are typically stronger than the current direct ones. We discuss the model-dependence of our results and briefly comment on how the forthcoming generation of high-resolution ultra-stable spectrographs will enable significantly tighter constraints.