Kavli Affiliate: Michael S. Turner
| First 5 Authors: Matilde Lopes Abreu, Michael S. Turner, , ,
| Summary:
The first year results of DESI 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
very strange behavior. They achieve a maximum dark energy density around
$zsimeq 0.4$ and rapidly decrease before and after. We explore
physics-motivated models where the dark energy is a rolling scalar-field. Each
of our four scalar-field models is 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. Each scalar field model makes different predictions for the age
of the Universe, which might be used to discriminate amongst them. For small
values of $beta$, the dimensionsless initial slope of the scalar field
potential links the predictions of different scalar field models. And for small
values of $beta$, $w_0w_a$ models can marginally represent the predictions of
a scalar-field model at the current precision needed. However, with
increasingly precise distance measurements, over a larger redshift range,
explicit modeling of the scalar-field evolution is already and will continue to
be essential to testing alternatives to $Lambda$.
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