Reionization History and Neutrino Mass

TL;DR

This study explores how different reionization histories impact neutrino mass estimates from cosmological data, finding that optical depth primarily influences the results.

Contribution

It demonstrates that reionization history details have minimal effect on neutrino mass constraints, which are mainly driven by total optical depth.

Findings

Reionization histories can shift neutrino mass estimates to positive values.

Total optical depth is the dominant factor affecting neutrino mass constraints.

Details of reionization history have only a minor impact on the results.

Abstract

Recent baryon acoustic oscillation (BAO) distance measurements, when combined with Cosmic Microwave Background (CMB) observations in the $\Lambda$CDM framework, lead to a preference for negative neutrino masses. We investigate whether this neutrino mass anomaly can be alleviated by a class of astrophysically motivated reionization histories. Using a frequentist analysis, we find that some reionization histories can move the best-fit value of $\sum m_\nu$ to a positive value and bring $\sum m_\nu\simeq0.06~{\rm eV}$ into the 95\% confidence interval. To separate the effect of the total optical depth from that of the details of the reionization history, we compare a high-$\tau$ history with a two-step tanh-like reionization history of the same $\tau$. The resulting $\Delta\chi^2(\sum m_\nu)$ profiles are nearly identical. This indicates that the effect is mainly driven by the total optical depth, while the details of the reionization history play only a minor role.