Kavli Affiliate: Michael S. Turner
| First 5 Authors: Matilde Lopes Abreu, Matilde Lopes Abreu, , ,
| Summary:
The first year results of DESI (DR1) provide evidence that dark energy may
not be quantum vacuum energy ($Lambda$). If true, this would be an
extraordinary development in the 25-year quest to understand cosmic
acceleration. The best-fit DESI $w_0w_a$ models for dark energy, which underpin
the claim, have strange behavior. They achieve a maximum energy density around
$zsimeq 0.5 $ and rapidly decrease before and after. We explore physics-based
models where the dark energy is a rolling scalar-field. Our four scalar-field
models are characterized by one dimensionless parameter $beta$, which in the
limit of $beta rightarrow 0$ reduces to $Lambda$CDM. While none of our
models fit the DESI data significantly better than $Lambda$CDM, for values of
$beta$ of order unity, they fit about as well as $Lambda$CDM. Alternatives to
vacuum energy make different predictions for the age of the Universe and are
potential discriminators. We also consider the second data release from DESI
(DR2), CMB data and supernovae data. The DR2 results are consistent with the
DR1, and the combination of DESI, CMB and SNe favor a 95% credible interval
$beta = 0.22 – 0.95$, providing modest evidence for a scalar-field explanation
for dark energy. While the DESI data prefer $w_0w_a$ to a scalar field, the SNe
data prefer a scalar field to $w_0w_a$. The robust DESI preference for
sharply-peaked dark energy may be telling us something important about dark
energy or the DESI data themselves.
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