Neutrino masses and mixing. Entering the era of subpercent precision

We perform an updated global analysis of the known and unknown parameters of the standard three neutrino (3ν) framework, using data available at the beginning of 2025. The known oscillation parameters include three mixing angles ðθ12; θ23; θ13Þ and two squared mass gaps, chosen as δm2 ¼ m2 2 − m2 1 > 0 and Δm2 ¼ m2 3 − 1 2 ðm2 1 þ m2 2Þ, where the discrete parameter α ¼ ignðΔm2Þ distinguishes normal ordering (NO, α ¼ þ1) from inverted ordering (IO, α ¼ −1). With respect to our previous 2021 update, the combination of accelerator, reactor, and atmospheric neutrino data leads to appreciably reduced uncertainties for θ23, θ13, and jΔm2j. In particular, jΔm2j is the first 3ν parameter to enter the domain of subpercent precision (0.8% at 1σ). We underline some issues about common systematics in combined fits that might affect (and possibly weaken) this error estimate. Concerning oscillation unknowns, we find a relatively weak preference for NO versus IO (at 2.2σ), for CP violation versus conservation in NO (1.3σ), and for the first θ23 octant versus the second in NO (1.1σ). We discuss the current status and qualitative prospects of the mass ordering hint in the plane charted by the mass parameters ðδm2; Δm2 eeÞ, where Δm2 ee ¼ jΔm2j þ 1 2 αðcos2θ12 − sin2θ12Þδm2, to be jointly measured by the JUNO experiment with subpercent precision. We also discuss upper bounds on nonoscillation observables, including the effective νe mass mβ in β decay, the effective Majorana mass mββ in 0νββ decay, and the sum of neutrino masses Σ in cosmology. We adopt mβ < 0.50 eV ð2σÞ from current 3 H data and report mββ < 0.086 eV (2σ) from a combined 76Ge, 130Te, and 136Xe data analysis, accounting for parametrized nuclear matrix element covariances. Concerning Σ, current results show tensions within the standard Λ cold dark matter (ΛCDM) cosmological model, pulling Σ toward unphysical values and suggesting possible model extensions. We discuss representative combinations of data, with or without augmenting the ΛCDM model with extra parameters accounting for possible systematics (lensing anomaly) or new physics (dynamical dark energy). The resulting 2σ upper limits are roughly spread around the bound Σ < 0.2 eV within a factor of 3 (both up- and downward), with different implications for NO and IO scenarios. Bounds from oscillation and nonoscillation data are also discussed in the planes charted by pairs of (mβ; mββ; Σ) parameters.