Thawing Dark Energy and Massive Neutrinos in Light of DESI (2503.00126v2)

Abstract: Recent analyses have shown that a dynamic dark energy modeled by the CPL parameterization of the dark energy equation of state (EoS) can ease constraints on the total neutrino mass compared to the standard $\Lambda$CDM model. This helps reconcile cosmological and particle physics measurements of $\sum m_\nu$. In this study, we investigate the robustness of this effect by assessing the extent to which the CPL assumption influences the results. We examine how alternative EoS parameterizations - such as Barboza-Alcaniz (BA), Jassal-Bagla-Padmanabhan (JBP), and a physically motivated thawing parameterization that reproduces the behavior of various scalar field models - affect estimates of $\sum m_\nu$. Although both the BA and JBP parameterizations relax the constraints similarly to the CPL model, the JBP parameterization still excludes the inverted neutrino mass hierarchy at $\sim 2.1\;\sigma$ with $\sum m_\nu < 0.096$~eV. The thawing parameterization excludes the inverted hierarchy at $\sim 3.3\sigma$ and yields tighter constraints, comparable to those of the $\Lambda$CDM model, with $\sum m_\nu < 0.071$~eV. Our analysis also reveals that the preference for unphysical negative neutrino masses is significantly reduced in all models considered. Finally, we show that the thawing model can be mapped into the BA and JBP $w_0$-$w_a$ parameter space, with the apparent preference for the phantom regime actually supporting quintessence (non-phantom) models.