Constraints on the sum of the neutrino masses in dynamical dark energy models with w(z)≥-1 are tighter than those obtained in ΛCDM

We explore cosmological constraints on the sum of the three active neutrino masses Mν in the context of dynamical dark energy (DDE) models with equation of state (EoS) parametrized as a function of redshift z by w(z)=w0+waz/(1+z), and satisfying w(z)≥-1 for all z. We make use of cosmic microwave background data from the Planck satellite, baryon acoustic oscillation measurements, and supernovae Ia luminosity distance measurements, and perform a Bayesian analysis. We show that, within these models, the bounds on Mν do not degrade with respect to those obtained in the ΛCDM case; in fact, the bounds are slightly tighter, despite the enlarged parameter space. We explain our results based on the observation that, for fixed choices of w0, wa such that w(z)≥-1 (but not w=-1 for all z), the upper limit on Mν is tighter than the ΛCDM limit because of the well-known degeneracy between w and Mν. The Bayesian analysis we have carried out then integrates over the possible values of w0-wa such that w(z)≥-1, all of which correspond to tighter limits on Mν than the ΛCDM limit. We find a 95% credible interval (C.I.) upper bound of Mν<0.13 eV. This bound can be compared with the 95% C.I. upper bounds of Mν<0.16 eV, obtained within the ΛCDM model, and Mν<0.41 eV, obtained in a DDE model with arbitrary EoS (which allows values of w<-1). Contrary to the results derived for DDE models with arbitrary EoS, we find that a dark energy component with w(z)≥-1 is unable to alleviate the tension between high-redshift observables and direct measurements of the Hubble constant H0. Finally, in light of the results of this analysis, we also discuss the implications for DDE models of a possible determination of the neutrino mass ordering by laboratory searches.