Kavli Affiliate: Joshua A. Frieman
| First 5 Authors: , , , ,
| Summary:
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$sigma$.
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