Probing gravitational non-minimal coupling with dark energy surveys
  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.
