Can dark energy be dynamical?

TL;DR

This paper critically examines the dynamical dark energy paradigm, highlighting its limitations, the sensitivity of parametric models to their functional forms, and the implications of reconstructed wiggles in the dark energy equation of state.

Contribution

It reveals the arbitrariness in parametric DDE models, analyzes the sensitivity of errors to model choices, and assesses the significance of wiggles in non-parametric reconstructions.

Findings

Errors in $w_a$ depend on the choice of $f(z)$ in parametric models.

The CPL model is among the least sensitive to DDE.

Reconstructed wiggles are confirmed at $ extless 2\sigma$ significance.

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 $\lesssim2\sigma$. 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.