Consistent Theories for the DESI dark energy fit

TL;DR

This paper investigates physically consistent models of evolving dark energy based on recent cosmological data, proposing new scenarios like the ramp model that fit observations well and are theoretically viable.

Contribution

It introduces the ramp model as a simple, consistent quintessence scenario that fits data better than LambdaCDM and aligns with effective field theory considerations.

Findings

The ramp model fits data better than LambdaCDM.

Non-linear corrections to the dark energy equation of state are weakly constrained.

Evolving dark energy can be realized through simple quintessence models.

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 early times, that is challenging to realize in consistent theories. Next, in the spirit of effective field theories, we consider the effect of higher order terms in the Taylor expansion of the equation of state of dark energy around the present epoch. We find that non-linear corrections of the equation of state are weakly constrained, thus opening the way to scenarios that differ from CPL at early times, possibly 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 $\Lambda$CDM, and only slightly worse than $w_0w_a$CDM, but with the notable advantage of being described by a simple and theoretically consistent lagrangian of a canonical quintessence model.