Observables sensitive to absolute neutrino masses: A reappraisal after WMAP-3y and first MINOS results

TL;DR

This work revisits constraints on the absolute neutrino masses using three observables: $m_\beta$ from beta decay, $m_{\beta\beta}$ from neutrinoless double beta decay, and $\Sigma= m_1+m_2+m_3$ from cosmology, incorporating the first MINOS results and WMAPP3 data. The authors combine oscillation data with non-oscillation probes and analyze multiple cosmological data sets to map the allowed parameter space, explicitly detailing the $\,\Delta m^2$ precision ($\sim$15% at $2\sigma$) and the evolving upper bounds on $\Sigma$ (from ~$2$ eV to ~$0.2$ eV) as more data are added and the degeneracy with $\sigma_8$ is broken. They examine the compatibility between $\Sigma$ and the claimed $0\nu\beta\beta$ signal, finding that compatibility hinges on the cosmological data set used; with conservative WMAP-3y data a global fit including the Kl04 claim is possible, while incorporating broader cosmological data generally disfavors the claim. The work then translates these mass bounds into predictions for forthcoming beta-decay and $0\nu\beta\beta$ experiments, highlighting that cosmology currently provides the strongest, most robust constraints on absolute neutrino masses, but that future experiments and cross-checks across multiple nuclei are essential due to nuclear-matrix-element uncertainties.

Abstract

In the light of recent neutrino oscillation and non-oscillation data, we revisit the phenomenological constraints applicable to three observables sensitive to absolute neutrino masses: The effective neutrino mass in single beta decay (m_beta); the effective Majorana neutrino mass in neutrinoless double beta decay (m_2beta); and the sum of neutrino masses in cosmology (Sigma). In particular, we include the constraints coming from the first Main Injector Neutrino Oscillation Search (MINOS) data and from the Wilkinson Microwave Anisotropy Probe (WMAP) three-year (3y) data, as well as other relevant cosmological data and priors. We find that the largest neutrino squared mass difference is determined with a 15% accuracy (at 2-sigma) after adding MINOS to world data. We also find upper bounds on the sum of neutrino masses Sigma ranging from ~2 eV (WMAP-3y data only) to ~0.2 eV (all cosmological data) at 2-sigma, in agreement with previous studies. In addition, we discuss the connection of such bounds with those placed on the matter power spectrum normalization parameter sigma_8. We show how the partial degeneracy between Sigma and sigma_8 in WMAP-3y data is broken by adding further cosmological data, and how the overall preference of such data for relatively high values of sigma_8 pushes the upper bound of Sigma in the sub-eV range. Finally, for various combination of data sets, we revisit the (in)compatibility between current Sigma and m_2beta constraints (and claims), and derive quantitative predictions for future single and double beta decay experiments.

Figures (7)

• Figure 1: Constraints placed by neutrino oscillation data on the parameters ($\Delta m^2,\,\sin^2\theta_{23},\,\sin^2\theta_{13}$), which are affected by the inclusion of the first MINOS results. The results are shown in terms of standard deviations from the best fit. Solid (dashed) lines refers to all neutrino oscillation data with (without) MINOS.
• Figure 2: Constraints placed by different cosmological data sets (1,...,7) on the sum of neutrino masses $\Sigma$, in terms of standard deviations from the best fit in each case.
• Figure 3: Joint $2\sigma$ constraints on the $(\sigma_8,\,\Sigma)$ parameters (95% C.L. for $N_\mathrm{DF}=1$) derived from four representative cosmological data sets (1, 2, 5, and 7, as listed in Table II).
• Figure 4: Superposition of $2\sigma$ constraints (95% C.L. for $N_\mathrm{DF}$=1) placed by $\beta$, $0\nu2\beta$, oscillation, and cosmological neutrino data in the three 2-dimensional projections of the $(m_\beta,\,m_{\beta\beta},\,\Sigma)$ parameter space. Cosmological constraints are labelled as in Table \ref{['tableCASES']} for the seven input data sets. The $0\nu2\beta$ lower limit on $m_{\beta\beta}$ from the claim in Kl04 is indicated as a horizontal dashed line.
• Figure 5: Comparison (at $2\sigma$) between the regions preferred by the $0\nu2\beta$ signal claim (horizontal band) and by all $\nu$ oscillation data plus $\beta$ and WMAP-3y data (slanted bands) for normal (NH) and inverted (IH) hierarchy, in the plane ($m_{\beta\beta},\Sigma$). The combination of all such data (thick slanted "wedge" in the upper right corner of the plot) corresponds to "Case $1^+$" in the text.