Bimetric gravity improves the fit to DESI BAO and eases the Hubble tension

We investigate whether the latest combination of the dark energy spectroscopic instrument (DESI) Year 3 data release (DR2) baryon acoustic oscillation measurements, cosmic microwave background (CMB) data ( 2018 + ACT ), and Type Ia supernovae (SNe Ia) compilations (Pantheon+, Union3, and DES Y5) favor a dynamical dark energy component, and explore if such a scenario can simultaneously help resolve the Hubble tension. We contrast two frameworks: the widely used phenomenological w 0 w a cold dark matter (CDM) model, and bimetric gravity—a fundamental modification of general relativity that naturally gives rise to phantom dark energy. The w 0 w a CDM model is moderately preferred over Λ CDM , at the 2 – 4 σ level, when fitting DESI DR2 + CMB + SNe Ia, but it exacerbates the Hubble tension. By comparison, bimetric gravity provides a modest improvement in fit quality, at the 1 σ level, but, by inferring H 0 = 69.0 ± 0.4 km / s / Mpc , it partially eases the Hubble tension, from a 5 σ discrepancy to a 3.7 σ tension. Including locally calibrated SNe Ia brings the overall preference for the bimetric model over Λ CDM to the 2 σ level, comparable to that of the w 0 w a CDM model when including the local SN Ia calibration.