Scalar field dark energy models: Current and forecast constraints
Anowar J. Shajib, Joshua A. Frieman
arXiv:2502.06929v2 Announce Type: replace
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 that we dub $w_phi$CDM. 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 BAO (DESI Data Release 2), the CMB (Planck and ACT), large-scale structure (DES Year-3 $3times2$pt), SNe Ia (DES-SN5YR), and strong lensing (TDCOSMO + SLACS), for $w_phi$CDM we obtain $w_0=-0.904_{-0.033}^{+0.034}$, 2.9$sigma$ 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 BAO+SNe Ia, for which $w_0=-0.837^{+0.044}_{-0.045}$, $3.6sigma$ 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 C. Rubin Observatory LSST), showing that the current best-fit $w_phi$CDM model will be distinguishable from $Lambda$CDM at over 9$sigma$.arXiv:2502.06929v2 Announce Type: replace
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 that we dub $w_phi$CDM. 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 BAO (DESI Data Release 2), the CMB (Planck and ACT), large-scale structure (DES Year-3 $3times2$pt), SNe Ia (DES-SN5YR), and strong lensing (TDCOSMO + SLACS), for $w_phi$CDM we obtain $w_0=-0.904_{-0.033}^{+0.034}$, 2.9$sigma$ 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 BAO+SNe Ia, for which $w_0=-0.837^{+0.044}_{-0.045}$, $3.6sigma$ 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 C. Rubin Observatory LSST), showing that the current best-fit $w_phi$CDM model will be distinguishable from $Lambda$CDM at over 9$sigma$.