Combined fit to 839048 atmospheric neutrino events from three experiments plus reactor data yields competitive mixing parameters with preference for normal mass ordering.
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Neutrino masses and mixing: Entering the era of subpercent precision
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abstract
We perform an updated global analysis of the known and unknown parameters of the standard $3\nu$ framework as of 2025. The known oscillation parameters include three mixing angles $(\theta_{12},\,\theta_{23},\,\theta_{13})$ and two squared mass gaps, chosen as $\delta m^2=m^2_2-m^2_1>0$ and $\Delta m^2=m^2_3-{\textstyle\frac{1}{2}}(m^2_1+m^2_2)$, where $\alpha=\mathrm{sign}(\Delta m^2)$ distinguishes normal ordering (NO, $\alpha=+1$) from inverted ordering (IO, $\alpha=-1$). With respect to our previous 2021 update, the combination of oscillation data leads to appreciably reduced uncertainties for $\theta_{23}$, $\theta_{13}$ and $|\Delta m^2|$. In particular, $|\Delta m^2|$ is the first $3\nu$ parameter to enter the domain of subpercent precision (0.8\% at $1\sigma$). We underline some issues about systematics, that might affect this error estimate. Concerning oscillation unknowns, we find a relatively weak preference for NO versus IO (at $2.2\sigma$), for CP violation versus conservation in NO (1.3$\sigma$) and for the first $\theta_{23}$ octant versus the second in NO ($1.1\sigma$). We discuss the status and qualitative prospects of the mass ordering hint in the plane $(\delta m^2,\,\Delta m^2_{ee})$, where $\Delta m^2_{ee}=|\Delta m^2|+{\textstyle\frac{1}{2}}\alpha(\cos^2\theta_{12}-\sin^2\theta_{12})\delta m^2$, to be measured by the JUNO experiment with subpercent precision. We also discuss upper bounds on nonoscillation observables. We report $m_\beta<0.50$~eV and $m_{\beta\beta}<0.086$~eV ($2\sigma$). Concerning the sum of neutrino masses $\Sigma$, we discuss representative combinations of data, with or without augmenting the $\Lambda$CDM model with extra parameters accounting for possible systematics or new physics. The resulting $2\sigma$ upper limits are roughly spread around the bound $\Sigma < 0.2$~eV within a factor of three. [Abridged]
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A sterile neutrino with a novel density-dependent matter potential Vs resolves multiple oscillation anomalies when Vs is negative and mixing angles are small.
JUNO's initial results combined with global data give a 2.2-2.3 sigma preference for normal neutrino mass ordering.
JUNO slow-mode data mildly prefer nonzero β_M1 (hinting Majorana neutrinos), while fast-mode RG shifts from β_D and β_M3 degrade mass-ordering sensitivity that TAO can restore.
A cuboid mass ansatz that sets mass angles equal to mixing angles predicts a nearly degenerate normal spectrum whose deviations from tribimaximal mixing are fixed by the observed mass-squared ratio.
A sign-switching dark energy model (Λ_s CDM) recovers positive effective neutrino masses (0.055 ± 0.050 eV) consistent with oscillation data, unlike ΛCDM which prefers negative values (-0.075 eV), for DESI DR2 + CMB + supernova fits with z_† > 2.4.
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Mu-tau interchange symmetry in the lepton mixing matrix leads to a potential divergence when tracing individual muon and tau neutrino fractions from astrophysical sources, so that only their sum plus the electron fraction can be extracted in the exact symmetry limit.
First JUNO data yields competitive bounds on decoherence and invisible decay parameters in neutrino oscillations while preserving standard oscillation measurements.
Assuming the KM3-230213A event comes from heavy dark matter decay, the preferred mass exceeds 100 PeV at 95% CL with lifetimes of 10^26-10^27 s, but these regions conflict with bounds from other neutrino telescopes and gamma-ray observations.
A dark matter fermion is shown to simultaneously explain the relic density, satisfy direct detection and collider bounds, and produce observable rates for muon-to-electron transitions in a viable parameter region.
JUNO's initial 59-day dataset constrains sterile neutrino mass splittings between 10^{-5} and 10^{-2} eV² down to sin²2θ₁₄ ~ O(10^{-1}) and scalar NSI |η_ee| below O(10^{-2}).
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