Can dark energy be dynamical?
Eoin Ó Colgáin, M. M. Sheikh-Jabbari, Lu Yin
Abstract
We highlight shortcomings of the dynamical dark energy (DDE) paradigm. For parametric models with an equation of state, $w(z)={w}_{0}+{w}_{a}f(z)$, 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 the 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 the 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 nonparametric 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 $\ensuremath{\lesssim}2\ensuremath{\sigma}$. 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.