Modified Gravity Realizations of Quintom Dark Energy after DESI DR2

Abstract We investigate the realization of quintom scenario for dynamical dark energy within modified gravity theories that can efficiently fit the recent observational data sets. Starting from a general effective field theory formulation of dark energy in metric-affine geometry, we derive the background action in unitary gauge and we demonstrate how both f ( T ) and f ( Q ) gravity can naturally realize quintom behavior through appropriate forms and parameter choices. Additionally, using the Gaussian process reconstruction of the latest Dark Energy Spectroscopic Instrument DR2 baryon acoustic oscillation data combined with Type Ia supernovae and cosmic microwave background observations, we extract the reconstructed dark-energy equation-of-state parameter, showing that it exhibits quintom-type evolution, crossing the phantom divide from below. Moreover, through detailed parameter estimations and application of information criteria, we compare the model with the quadratic one and the ΛCDM model. Our results show that, due to its rich structure, modified gravity stands as one of the main candidates for the realization of the data-favored dynamical dark energy.