Evolving dark energy models: Current and forecast constraints (2502.06929v1)

Abstract: 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. We provide a quasi-universal, quasi-one-parameter functional fit to the scalar-field $w_\phi(z)$ that captures the behavior of these models more informatively than the standard $w_0w_a$ phenomenological parametrization; their behavior is completely described by the current value of the equation-of-state parameter, $w_0=w(z=0)$. Combining current data from SNe Ia (DES-SN5YR), BAO (SDSS + DESI Year 1), the CMB (Planck and ACT), large-scale structure (DES Year-3 $3\times2$pt), and strong lensing (TDCOSMO + SLACS), we obtain $w_0=-0.908\pm0.035$, 2.6$\sigma$ discrepant from the $\Lambda$ cold dark matter ($\Lambda$CDM) model. The Bayesian evidence ratio substantially favors this $w_\phi$CDM model over $\Lambda$CDM. The data combination that yields the strongest discrepancy with $\Lambda$CDM is SNe Ia+BAO, for which $w_0=-0.840^{+0.048}_{-0.050}$, $3.2\sigma$ discrepant from $\Lambda$CDM and with a Bayesian evidence ratio strongly in favor. We find that the so-called $S_8$ 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 Rubin Observatory LSST), showing that the current best-fit $w_\phi$CDM model will be distinguishable from $\Lambda$CDM at over 9$\sigma$.