Consistent theories for the DESI dark energy fit

Abstract We search for physically consistent realizations of evolving dark energy suggested by the cosmological fit of DESI, Planck and Supernovae data. First we note that any lagrangian description of the standard Chevallier-Polarski-Linder (CPL) parametrization for the dark energy equation of state w , allows for the addition of a cosmological constant. We perform the cosmological fit finding new regions of parameter space that however continue to favour dark energy with w -1 at all times. We present indeed scenarios where evolving dark energy can be realized through quintessence models. We introduce in particular the ramp model where dark energy coincides with CPL at late times and approximates to a cosmological constant at early times. The latter model provides a much better fit than ΛCDM, and only slightly worse than w 0 w a CDM, but with the notable advantage of being described by a simple and theoretically consistent lagrangian of a canonical quintessence model.