Can dark energy be dynamical?. (arXiv:2104.01930v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Colgain_E/0/1/0/all/0/1">Eoin &#xd3; Colg&#xe1;in</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sheikh_Jabbari_M/0/1/0/all/0/1">M. M. Sheikh-Jabbari</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yin_L/0/1/0/all/0/1">Lu Yin</a>

We highlight shortcomings of the dynamical dark energy (DDE) paradigm. For
parametric models with equation of state (EOS), $w(z) = w_0 + w_a f(z)$ for a
given function of redshift $f(z)$, we show that the errors in $w_a$ are
sensitive to $f(z)$: if $f(z)$ increases quickly with redshift $z$, then errors
in $w_a$ are smaller, and vice versa. As a result, parametric DDE models suffer
from a degree of arbitrariness and focusing too much on one model runs that
risk that DDE may be overlooked. In particular, we show the ubiquitous
Chevallier-Polarski-Linder model is one of the least sensitive to DDE. We also
comment on “wiggles” in $w(z)$ uncovered in non-parametric reconstructions.
Concretely, we isolate the most relevant Fourier modes in the wiggles, model
them and fit them back to the original data to confirm the wiggles at
$lesssim2sigma$. We delve into the assumptions going into the reconstruction
and argue that the assumed correlations, which clearly influence the wiggles,
place strong constraints on field theory models of DDE.

We highlight shortcomings of the dynamical dark energy (DDE) paradigm. For
parametric models with equation of state (EOS), $w(z) = w_0 + w_a f(z)$ for a
given function of redshift $f(z)$, we show that the errors in $w_a$ are
sensitive to $f(z)$: if $f(z)$ increases quickly with redshift $z$, then errors
in $w_a$ are smaller, and vice versa. As a result, parametric DDE models suffer
from a degree of arbitrariness and focusing too much on one model runs that
risk that DDE may be overlooked. In particular, we show the ubiquitous
Chevallier-Polarski-Linder model is one of the least sensitive to DDE. We also
comment on “wiggles” in $w(z)$ uncovered in non-parametric reconstructions.
Concretely, we isolate the most relevant Fourier modes in the wiggles, model
them and fit them back to the original data to confirm the wiggles at
$lesssim2sigma$. We delve into the assumptions going into the reconstruction
and argue that the assumed correlations, which clearly influence the wiggles,
place strong constraints on field theory models of DDE.

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