Non-minimally coupled gravity constraints from DESI DR2 data

It has been observed that the hint about phantom crossing in the DESI BAO observation might point to non-minimally coupled gravity. We analyzed DESI DR2 BAO together with CMB and Type Ia supernova data to constrain non-minimal coupling of gravity in the effective field theory (EFT) approach. Using a non-parametric method to infer the EFT functions, we found that with DESI BAO, DESY5 SN, and Planck CMB data the signal for non-minimal coupling reaches $\sim3\sigma$. It is found that current data can constrain up to the quadratic order $(n=2)$ if the EFT function representing non-minimal coupling is Taylor expanded as a general function of the dark energy fraction $\Omega_{\rm{DE}}$, i.e. $\Omega^{\text{EFT}}(a)=\sum_{i=0}^{n} c^{\rm{EFT}}_i \Omega^i_{\text{DE}}(a)$. This calls for a more flexible parametrization of the EFT functions than commonly used ones in literature.