Assuming higher reionization optical depth yields tentative neutrino mass detection and eases cosmological tensions
A new analysis shows that adopting a larger optical depth to reionization aligns early- and late-Universe measurements within the standard ΛCDM model and provides a 2σ indication of a total neutrino mass of about 0.1 eV.
Researchers have re-examined cosmological data by imposing a higher prior on the optical depth to reionization (τ = 0.11 ± 0.006). The revised τ value reduces discrepancies between cosmic microwave background (CMB) measurements and late-time observations such as Dark Energy Spectroscopic Instrument (DESI) baryon acoustic oscillation and full-shape galaxy data. Under this high-τ scenario, the combined neutrino mass is inferred to be Σmν = 0.10^{+0.04}{-0.05} eV (68 % confidence), marking the first tentative 2σ detection of a positive neutrino mass from cosmological probes. The model also restores consistency for the Hubble constant and yields dark-energy equation-of-state parameters compatible with a cosmological constant, even when supernova data are included. The authors note that forthcoming large-scale CMB polarization experiments such as LiteBIRD, CLASS and the proposed PICO mission could test the elevated τ prior and further clarify the neutrino mass and dark-energy properties.
