Status of neutrino cosmology: Standard <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi mathvariant="normal">Λ</mml:mi> <mml:mi>CDM</mml:mi> </mml:mrow> </mml:math> , extensions, and tensions
Helena García Escudero, Kevork N. Abazajian
Abstract
We examine the performance of the six-parameter $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ 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 ($\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}$). Our results show upper limits in the range of $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}<76.9\text{ }\text{ }\mathrm{meV}$ to $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}<108\text{ }\text{ }\mathrm{meV}$ (95% CL). The variation in the limits on $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}$ 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 $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}$. In the context of hierarchical mass models in $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, we find a $1.47\ensuremath{\sigma}$ 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 $1.36\ensuremath{\sigma}$. We find that a ``negative'' neutrino mass, inferred from the shape of the likelihood in the physical regime, $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}>0$, is only present at less than $2\ensuremath{\sigma}$. The strong $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}$ constraints originate primarily from the high CMB lensing signal, which disfavors the suppression of power from $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}$, 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 ${N}_{\mathrm{eff}}\ensuremath{\approx}3.5$, alleviate the Hubble tension. Significantly, we find a $3.3\ensuremath{\sigma}$ 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 $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ 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 $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}$ and ${N}_{\mathrm{eff}}$, finding consistency with $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ parameters except for the dark energy equation of state, ${w}_{0}=\ensuremath{-}0.96{1}_{\ensuremath{-}0.037}^{+0.012}$. Neutrino mass constraints in this extended model remain stringent, with $\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}<97.0\text{ }\text{ }\mathrm{meV}$ (95% CL).