DESI DR1 Reanalysis Sets Neutrino Mass Limit That Appears to Disfavor Inverted Ordering

A newly accepted Physical Review D paper reports that an independent reanalysis of public data from the Dark Energy Spectroscopic Instrument’s first data release, or DESI DR1, finds a neutrino-mass limit tight enough to formally disfavor the inverted neutrino mass ordering.

The result comes with an immediate caution. The paper’s headline limit in the standard ΛCDM cosmology model is a 95% confidence upper bound of 0.049 electron volts for the summed neutrino mass, while neutrino oscillation measurements — which measure mass differences between neutrino types — imply a minimum total of about 0.058 eV even for the normal ordering, and about 0.098 eV for the inverted ordering. That puts the cosmological upper limit below the usual floor for the normal case too, making the finding striking but not straightforward to interpret.

The paper, “Reanalyzing DESI DR1: 4. Percent-Level Cosmological Constraints from Combined Probes and Robust Evidence for the Normal Neutrino Mass Hierarchy,” is arXiv:2601.16165. Its latest arXiv version is v3, dated Aug. 28, 2026, and it is listed as accepted to Physical Review D on Aug. 25. The authors are Mikhail M. Ivanov, James M. Sullivan, Roger de Belsunce, Shi-Fan Chen, Anton Chudaykin, Mark Maus and Oliver H. E. Philcox. The analysis is not an official DESI Collaboration result. Instead, it is an outside team’s reanalysis of public DESI DR1 cosmology data, combining DESI DR1 galaxy-clustering full-shape measurements with DESI baryon acoustic oscillation data, photometric galaxy clustering, cosmic microwave background lensing cross-correlations and Planck priors on the spectral tilt and baryon density. Some combinations also include Pantheon+ supernova data or Planck cosmic microwave background data.

In ΛCDM, the authors report a 95% confidence upper limit of (M_\nu < 0.049) eV. They say that level is enough to disfavor the inverted hierarchy at about 3.5 sigma, a statistical measure of significance. In a broader cosmological model with time-varying dark energy, known as (w_0w_a)CDM, the paper reports (M_\nu < 0.077) eV at 95% confidence and says the inverted hierarchy is disfavored at about 2.4 sigma. The paper also presents broader precision cosmology results; in ΛCDM, for example, it reports a Hubble constant of (H_0 = 69.08 \pm 0.37) kilometers per second per megaparsec.

Those neutrino numbers matter because oscillation experiments do not directly give the full masses, but they do fix the spacing between them, which in turn sets a minimum possible total. That is why cosmological upper limits below roughly 0.10 eV begin to squeeze the inverted ordering, while limits below roughly 0.06 eV start to create tension even for the normal ordering. The authors explicitly discuss possible reasons for that tension, including model dependence, tensions between datasets and possible unknown systematics. Recent DESI-related analyses had already pushed cosmological neutrino limits to around 0.07 eV depending on the data combination and assumptions, but this paper goes further and frames the result as hierarchy-level evidence. As of Aug. 31, no formal public statement had been identified from the DESI Collaboration endorsing or rebutting this specific reanalysis.