Impacts of dark energy on weighing neutrinos: Mass hierarchies considered

Abstract

Taking into account the mass splittings between three active neutrinos, we investigate the impacts of dark energy on constraining the total neutrino mass ∑m_ν by using recent cosmological observations. We consider two typical dark energy models, namely, the w CDM model and the holographic dark energy (HDE) model, which both have an additional free parameter compared with the Λ CDM model. We employ the Planck 2015 data of CMB temperature and polarization anisotropies, combined with low-redshift measurements on BAO distance scales, type Ia supernovae, the Hubble constant, and Planck lensing. Compared to the Λ CDM model, our study shows that the upper limit on ∑m_ν becomes much looser in the w CDM model but much tighter in the HDE model. In the HDE model, we obtain the 95% confidence level upper limit ∑m_ν<0.105 eV for three degenerate neutrinos. This might be the most stringent constraint on ∑m_ν by far, and it is on the verge of diagnosing the neutrino mass hierarchies in the HDE model. However, the difference of χ² is still not significant enough to distinguish the neutrino mass hierarchies, even though the minimal χ² of the normal hierarchy is slightly smaller than that of the inverted hierarchy.