Status of neutrino cosmology: Standard ΛCDM, extensions, and tensions

We examine the performance of the six-parameter Lambda CDM model and its extensions in light of recent cosmological observations, with particular focus on neutrino properties inferred from cosmology. Using a broad suite of nine combinations of datasets, with three separate analyses of the Planck cosmic microwave background (CMB) data, and three separate survey datasets of supernovae (SNe), plus the recent DESI baryon acoustic oscillation (BAO) scale results, we derive constraints on the sum of neutrino masses (Sigma mv). Our results show upper limits in the range of Sigma mv < 76.9 meV to Sigma mv < 108 meV (95% CL). The variation in the limits on Sigma mv arises from the separate analyses of the Planck CMB data and the separate supernova datasets, as they relate to the inferred matter density and its relation to the sensitivity of the BAO scale and CMB lensing to Sigma mv. In the context of hierarchical mass models in Lambda CDM, we find a 1.47 sigma preference for normal ordering (NO) over inverted ordering (IO), with similar values of preference across all datasets. Despite the strong constraints, an inclination toward the nonstandard massless neutrinos over NO remains weak at 1.36 sigma. We find that a "negative" neutrino mass, inferred from the shape of the likelihood in the physical regime, Sigma mv > 0, is only present at less than 2 sigma. The strong Sigma mv constraints originate primarily from the high CMB lensing signal, which disfavors the suppression of power from Sigma mv, and the DESI BAO scale, which is complementary to that from the suppression of power. We confirm that models allowing extra relativistic degrees of freedom, with N-eff approximate to 3.5, alleviate the Hubble tension. Significantly, we find a 3.3 sigma preference for a 0.1 eV partially thermalized sterile neutrino when the SH0ES H-0 measurement is included, a scale of interest in short-baseline oscillation experiment results. When H-0 is included, fully thermalized sterile neutrino models are as consistent as Lambda CDM in fitting all datasets, but are disfavored otherwise. We also explore an 11-parameter model relaxing the dark energy equation of state and curvature, together with Sigma mv and N-eff, finding consistency with Lambda CDM parameters except for the dark energy equation of state, w(0) = -0.961(-0.037)(+0.012). Neutrino mass constraints in this extended model remain stringent, with Sigma mv < 97.0 meV (95% CL).