# Impact of theoretical priors in cosmological analyses: the case of single field quintessence

## TL;DR

This paper examines how theoretical stability conditions influence the viability of single field Quintessence models in explaining dark energy, showing that such conditions significantly restrict the parameter space and challenge their compatibility with observational data.

## Contribution

It demonstrates that stability and viability constraints substantially limit single field Quintessence models, impacting their ability to fit cosmological observations.

## Key findings

- Stable single field Quintessence models are disfavored compared to LCDM.
- Theoretical conditions eliminate favored regions in the CPL parameter space.
- Weak lensing data suggests the need for multiple fields for stability.

## Abstract

We investigate the impact of general conditions of theoretical stability and cosmological viability on dynamical dark energy models. As a powerful example, we study whether minimally coupled, single field Quintessence models that are safe from ghost instabilities, can source the CPL expansion history recently shown to be mildly favored by a combination of CMB (Planck) and Weak Lensing (KiDS) data. We find that in their most conservative form, the theoretical conditions impact the analysis in such a way that smooth single field Quintessence becomes significantly disfavored with respect to the standard LCDM cosmological model. This is due to the fact that these conditions cut a significant portion of the (w0;wa) parameter space for CPL, in particular eliminating the region that would be favored by weak lensing data. Within the scenario of a smooth dynamical dark energy parametrized with CPL, weak lensing data favors a region that would require multiple fields to ensure gravitational stability.