Bayesian model selection on scalar ε-field dark energy

The main aim of this paper is to analyze minimally coupled scalar fields-quintessence and phantom-as the main candidates to explain the accelerated expansion of the Universe and compare its observables to current cosmological observations; as a byproduct we present its PYTHON module. This work includes a parameter epsilon which allows to incorporate both quintessence and phantom fields within the same analysis. Examples of the potentials, so far included, are V(phi) = V-0 phi(mu)e(beta phi u) and V(phi) = V (0) (cosh(alpha phi) + beta) with alpha, mu, and beta being free parameters, but the analysis can be easily extended to any other scalar field potential. Additional to the field component and the standard content of matter, the study also incorporates the contribution from spatial curvature (Omega(k)), as it has been the focus in recent studies. The analysis contains the most up-to-date data sets along with a nested sampler to produce posterior distributions along with the Bayesian evidence, that allows to perform a model selection. In this work, we constrain the parameter space describing the two generic potentials, and among several combinations, we found that the best fit to current data sets is given by a model slightly favoring the quintessence field with potential V(phi) = V-0 phi(mu)e(beta phi) with beta = 0.22 +/- 1.56, mu = -0.41 +/- 1.90, and slightly negative curvature Omega(k,0) = -0.0016 +/- 0.0018, which presents deviations of 1.6 sigma from the standard lambda cold dark matter (Lambda CDM) model. Even though this potential contains three extra parameters, the Bayesian evidence B-Lambda,B-phi = 2.0 is unable to distinguish this model compared to the Lambda CDM with curvature (Omega(k,0) = 0.0013 +/- 0.0018). The potential that provides the minimal Bayesian evidence corresponds to V(phi) = V (0) cosh(alpha phi) with alpha = -0.61 +/- 1.36.

Automated summary

This paper analyzes minimally coupled scalar fields - quintessence and phantom - as candidates to explain the accelerated expansion of the Universe, comparing their observables to current cosmological observations. By constraining the parameter space of two generic potentials and analyzing the data sets, it was found that the model slightly favoring quintessence field fits best with current data. Despite containing three extra parameters, this model cannot be distinguished from the standard ΛCDM model with curvature based on Bayesian evidence. The potential with minimal Bayesian evidence corresponds to a specific form of the scalar field potential.