Non-Minimally Coupled Quintessence in Light of DESI

Abstract: We analyze a model of quintessence governed by an exponential potential and non-minimally coupled to gravity, in light of recent datasets, including cosmic microwave background, baryon acoustic oscillations, and supernovae distance moduli observations. Mainly focusing on the Palatini formulation of gravity, a phase space analysis reveals the existence of a late-time stable de Sitter attractor as long as the non-minimal coupling constant is negative, regardless of the value of the slope of the exponential. Fitting to CMB+DESI+DESY5 data, we find strong evidence for our model over $\Lambda$CDM, with a Bayes factor $\log B = 5.52$. Furthermore, the data seem to prefer dynamical dark energy at $>3\sigma$ C.L. and a phantom crossing in the barotropic parameter of dark energy at $2-3\sigma$ C.L.. We find that the scalar field dynamics in the Palatini formalism provides marginally better agreement to the data compared to the metric formalism.