DESI 2024: Constraints on physics-focused aspects of dark energy using DESI DR1 BAO data

Baryon acoustic oscillation data from the first year of the Dark Energy Spectroscopic Instrument (DESI) provide near percent-level precision of cosmic distances in seven bins over the redshift range $z=0.1--4.2$. This paper is the follow-up to the original DESI BAO cosmology paper [A. G. Adame et al. (DESI Collaboration), arXiv:2404.03002], which considered the conventional ${w}_{0}{w}_{a}$ cold dark matter (CDM) model. We use the novel DESI data, together with other cosmic probes, to constrain the background expansion history using some well-motivated physical classes of dark energy. In particular, we explore three physics-focused behaviors of dark energy from the equation of state and energy density perspectives: the thawing class (matching many simple quintessence potentials), emergent class (where dark energy comes into being recently, as in phase transition models), and mirage class [where phenomenologically the distance to cosmic microwave background (CMB) last scattering is close to that from a cosmological constant $\mathrm{\ensuremath{\Lambda}}$ despite dark energy dynamics]. All three classes fit the data at least as well as $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, and indeed can improve on it by $\mathrm{\ensuremath{\Delta}}{\ensuremath{\chi}}^{2}\ensuremath{\approx}\ensuremath{-}5$ to $\ensuremath{-}17$ for the combination of DESI BAO with CMB and supernova data while having one more parameter. The mirage class does essentially as well as ${w}_{0}{w}_{a}\mathrm{CDM}$ and exhibits moderate to strong Bayesian evidence preference with respect to $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$. These classes of dynamical behaviors highlight worthwhile avenues for further exploration into the nature of dark energy.

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