Can dark energy be dynamical?

Abstract

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 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 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 $\lesssim 2\ddot{I}ƒ$. 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.

11 pages, comments welcome, in particular sightings in the literature of the wa errors varying across DDE models in line with the outlined trend; v2, plot & comments added, accepted to PRD