Scale and redshift dependent limits on cosmic neutrino properties

TL;DR

Neutrino masses and abundances are tightly constrained cosmologically, but their stability across redshift and scale remains to be tested. The authors implement scale-, redshift-, and redshift–scale binning of $\sum m_\nu$ and $N_{\rm eff}$ within a CAMB-based framework and analyze Planck 2018 CMB along with DESY1, WiggleZ, and MPS data via MCMC. They find the strongest $\sum m_\nu$ bounds in the $[10^{-3},10^{-2}]\,h$/Mpc bin ($<0.54$ eV at 95% CL) and observe 2–3$\sigma$ hints for non-zero mass in the $[100,1100]$ redshift and $[10^{-2},10^{-1}]$ h/Mpc bin, while $N_{\rm eff}$ constraints from intermediate scales are robust and consistent with $N_{\rm eff}\approx3.04$; allowing $N_{\rm eff}$ to vary tightens the global neutrino-mass bound to $\sum m_\nu<0.205$ eV. The results identify the most informative scales and epochs for neutrino properties and provide guidance for upcoming surveys to maximize sensitivity to neutrino physics.

Abstract

Cosmological neutrino mass and abundance measurements are reaching unprecedented precision. Testing their stability versus redshift and scale is a crucial issue, as it can serve as a guide for optimizing ongoing and future searches. Here, we perform such analyses, considering a number of redshift, scale, and redshift-and-scale nodes. Concerning the $k$-space analysis of $\sum m_ν$, CMB observations are crucial, as they lead the neutrino mass constraints. Interestingly, some data combinations suggest a non-zero value for the neutrino mass with $2σ$ significance. The most constraining bound we find is $\sum m_ν<0.54$ eV at $95\%$ CL in the $[10^{-3}, 10^{-2}]$ $h$/Mpc $k$-bin, a limit that barely depends on the data combination. Regarding the redshift- and scale-dependent neutrino mass constraints, high redshifts ($z>100$) and scales in the range $[10^{-3}, 10^{-1}]$ $h$/Mpc provide the best constraints. The least constraining bounds are obtained at very low redshifts $[0,0.5]$ and also at very small scales ($k>0.1\, h$/Mpc), due to the absence of observations. Highly relevant is the case of the $[100, 1100]$, $[10^{-2}, 10^{-1}]$ $h$/Mpc redshift-scale bin, where a $2$-$3σ$ evidence for a non-zero neutrino mass is obtained for all data combinations. The bound from CMB alone at $68\%$ CL is $0.63^{+0.20}_{-0.24}$ eV, and the one for the full dataset is $0.56^{+0.20}_{-0.23}$ eV, clearly suggesting a non-zero neutrino mass at these scales, possibly related to a deviation of the ISW amplitude in this redshift range. Concerning the analysis of $N_{\rm eff}$ in the $k$-space, at intermediate scales ranging from $k=10^{-3}$ $h$/Mpc to $k=10^{-1}$ $h$/Mpc, accurate CMB data provide very strong bounds, the most robust one being $N_{\rm eff}=3.09\pm 0.14$, comparable to the standard expected value without a $k$-bin analysis. [abridged]

Figures (8)

• Figure 1: The tomographic reconstruction of neutrino masses across cosmic scales from CMB data.
• Figure 2: One-dimensional and two-dimensional marginalized constraints on the scale-dependent neutrino mass model from CMB, CMB plus DESY1, CMB plus MPK and CMB plus DESY1 plus MPK datasets, respectively.
• Figure 3: $2\sigma$ bounds on neutrino masses in the redshift- and scale-dependent neutrino mass model from CMB data. Note that all bins have $2\sigma$ upper bounds except for $\Sigma m_\nu^{64}$, which has a $2\sigma$ lower limit of 1.76 eV. The value "10.00" denotes parameters that remain unconstrained by the data.
• Figure 4: One-dimensional and two-dimensional marginalized constraints on the scale-dependent number of relativistic species model without massive neutrinos from CMB, CMB plus DESY1, CMB plus MPS and CMB plus DESY1 plus MPS datasets, respectively.
• Figure 5: The tomographic reconstructions of the number of relativistic species across cosmic scales from CMB data. The blue lines denote the standard prediction of $N_{\rm eff}=3.044$, and the red dashed lines represent the best fit corresponding to the mean value of posterior distribution in each bin.