Recent results from type Ia supernovae (SNe Ia) and baryon acoustic oscillations (BAO), in combination with cosmic microwave background (CMB) measurements, have focused renewed attention on dark energy models with a time-varying equation-of-state parameter, w(z). In this paper, we describe the simplest, physically motivated models of evolving dark energy that are consistent with the recent data, a broad subclass of the so-called thawing scalar-field models that we dub wϕCDM. We provide a quasiuniversal, quasi-one-parameter functional fit to the scalar-field wϕ(z) that captures the behavior of these models more informatively than the standard w0wa phenomenological parametrization; their behavior is completely described by the current value of the equation-of-state parameter, w0=w(z=0). Combining current data from BAO (DESI data release 2), the CMB ( and ACT), large-scale structure (DES year-3 3×2pt), SNe Ia (DES-SN5YR), and strong lensing (TDCOSMO+SLACS), for wϕCDM, we obtain w0=−0.904−0.033+0.034, 2.9σ discrepant from the Λ cold dark matter (ΛCDM) model. The Bayesian evidence ratio substantially favors this wϕCDM model over ΛCDM. The data combination that yields the strongest discrepancy with ΛCDM is BAO+SNe Ia, for which w0=−0.837−0.045+0.044, 3.6σ discrepant from ΛCDM and with a Bayesian evidence ratio strongly in favor. We find that the so-called S8 tension between the CMB and large-scale structure is slightly reduced in these models, while the Hubble tension is slightly increased. We forecast constraints on these models from near-future surveys (DESI-extension and the Vera C. Rubin Observatory LSST), showing that the current best-fit wϕCDM model will be distinguishable from ΛCDM at over 9σ.
Shajib et al. (2025) studied this question.