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 ξ. The value of ξ 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 ξ 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 ξ>0.289 where ξ=0 is excluded outside the 95% confidence region. The effective gravitational constant Geff subject to the hint of a non-zero ξ is constrained to -0.003<1-Geff/G<0.033 at the same confidence level on cosmological scales, and it can be narrowed down to 1-Geff/G<2.2×10-5 when combining with Solar System tests.