Probing gravitational non-minimal coupling with dark energy surveys

TL;DR

This paper constrains a non-minimal coupling in dark energy models using multiple cosmological observations, finding evidence for a positive coupling parameter and setting tight bounds on deviations from standard gravity.

Contribution

It provides observational constraints on a quadratic coupling between the quintessence field and curvature, exploring models where the coupling is a free parameter and combining diverse data sets.

Findings

Best-fit coupling parameter $\xi > 0.289$ with $\xi=0$ excluded at 95% confidence

Effective gravitational constant constrained to within 3.3% on cosmological scales

Solar System tests further tighten the bounds to $2.2 imes 10^{-5}$

Abstract

We investigate observational constraints on a specific one-parameter extension to the minimal quintessence model, where the quintessence field acquires a quadratic coupling to the scalar curvature through a coupling constant $\xi$. The value of $\xi$ is highly suppressed in typical tracker models if the late-time cosmic acceleration is driven at some field values near the Planck scale. We test $\xi$ in a second class of models in which the field value today becomes a free model parameter. We use the combined data from type-Ia supernovae, cosmic microwave background, baryon acoustic oscillations and matter power spectrum, to weak lensing measurements and find a best-fit value $\xi > 0.289$ where $\xi = 0$ is excluded outside the 95 per cent confidence region. The effective gravitational constant $G_{\rm eff}$ subject to the hint of a non-zero $\xi$ is constrained to $-0.003 < 1- G_{\rm eff}/G < 0.033$ at the same confidence level on cosmological scales, and can be narrowed down to $1- G_{\rm eff}/G < 2.2 \times 10^{-5}$ when combining with Solar System tests.