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arXiv · 2605.10116

Reionization History and Neutrino Mass

YiCheng Dai·Wei Liao
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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.

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YiCheng Dai, Wei Liao. 2026-05-11. Reionization History and Neutrino Mass. https://arxiv.org/abs/2605.10116

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