## Monday, January 29, 2018

### Alternative Dark Energy Theories Further Tighten Bound On Neutrino Masses

Many investigators favor a form of dark energy that can vary over time to the cosmological constant, although both theories can fit the evidence within the bounds of statistical significance. A varying dark energy cosmology, when applied to available data, more tightly bounds the upper limit to the sum of the neutrino masses.
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 perform a Bayesian analysis and show that, within these models, the bounds on Mν\textit{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 Mνthan the ΛCDM limit. We find a 95\% confidence level (C.L.) upper bound of Mν<0.13eV. This bound can be compared with Mν<0.16eV at 95\%~C.L., obtained within the ΛCDM model, and Mν<0.41eV at 95\%~C.L., 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 hierarchy by laboratory searches. (abstract abridged)
Sunny Vagnozzi, et al., "Constraints on the sum of the neutrino masses in dynamical dark energy models with w(z)≥−1 are tighter than those obtained in ΛCDM" (January 25, 2018).