Probing gravitational non-minimal coupling with dark energy surveys

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 $G_{\mathrm{eff}}$ subject to the hint of a non-zero $\xi$ is constrained to $-0.003<1-G_{\mathrm{eff}}/G<0.033$ at the same confidence level on cosmological scales, and can be narrowed down to $1-G_{\mathrm{eff}}/G<2.2\times 10^{-5}$ when combining with Solar System tests.

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