Status of global fits to neutrino oscillations

TL;DR

The paper synthesizes the status of global neutrino-oscillation analyses by integrating the latest KamLAND and K2K data with solar and atmospheric measurements, delivering a comprehensive three-flavour fit and assessing robustness to solar-model and non-standard physics. It shows that atmospheric data favor near-maximal νμ–ντ mixing with Δm^2 in the atmospheric range, while solar data (especially KamLAND) solidify the LMA solution with Δm^2_sol around 8×10^-5 eV^2 and sin^2θ_sol around 0.29, simultaneously tightening the bound on θ13. The LSND anomaly is examined in four-neutrino frameworks (3+1 and 2+2), and the combined data robustly disfavour 2+2 schemes and disfavor 3+1 schemes, highlighting a significant tension that would require new experimental confirmation to resolve. The work also discusses robustness against non-standard interactions, spin-flavour precession, and neutrino magnetic moments, concluding that the standard oscillation picture remains the dominant interpretation. Overall, KamLAND’s impact on solar-oscillation parameter determination and the tightening of θ13 bounds mark important progress, while LSND-related explanations for a sterile neutrino remain an open puzzle demanding further experimental input.

Abstract

We review the present status of global analyses of neutrino oscillations, taking into account the most recent neutrino data including the latest KamLAND and K2K updates presented at Neutrino2004, as well as state-of-the-art solar and atmospheric neutrino flux calculations. We give the two-neutrino solar + KamLAND results, as well as two-neutrino atmospheric + K2K oscillation regions, discussing in each case the robustness of the oscillation interpretation against departures from the Standard Solar Model and the possible existence of non-standard neutrino physics. Furthermore, we give the best fit values and allowed ranges of the three-flavour oscillation parameters from the current worlds' global neutrino data sample and discuss in detail the status of the small parameters $α\equiv \Dms/\Dma$ as well as $\sin^2θ_{13}$, which characterize the strength of CP violating effects in neutrino oscillations. We also update the degree of rejection of four-neutrino interpretations of the LSND anomaly in view of the most recent developments.

Figures (28)

• Figure 1: Allowed ($\sin^2\theta_\textsc{atm}$, $\Delta m^2_\textsc{atm}$) regions at 90%, 95%, 99%, and 3$\sigma$ C.L. for 2 d.o.f. The regions delimited by the lines correspond to atmospheric data only, while for the colored regions also K2K data are added. The best fit point of atmospheric (atmospheric + K2K) data is marked by a triangle (star). Also shown is the $\Delta \chi^2$ as a function of $\sin^2\theta_\textsc{atm}$ and $\Delta m^2_\textsc{atm}$, minimized with respect to the undisplayed parameter.
• Figure 2: Allowed K2K regions in the ($\sin^2\theta_\textsc{atm}$, $\Delta m^2_\textsc{atm}$) plane at 90%, 95%, 99%, and 3$\sigma$ C.L. for 2 d.o.f. The hollow lines delimit the region determined from the atmospheric data only. The star (triangle) corresponds to the K2K (atmospheric) best fit point.
• Figure 3: Effective flavour-changing NSI operator.
• Figure 4: Atmospheric neutrino oscillation parameters from fornengo:2001pm fitted in the presence of non-standard interactions using the Bartol flux barr:1989ru. We show the behaviour of the $\chi^2$ as a function of the four parameters $\Delta m^2_\textsc{atm}$ (upper left), $\sin^2 2\theta_\textsc{atm}$ (lower left), the FC parameter $\varepsilon$ (upper right), and the NU parameter $\varepsilon'$ (lower right). In each panel the $\chi^2$ is minimized with respect to the three undisplayed parameters. In the left panels we show also the pure oscillation case (OSC), with $\varepsilon$ and $\varepsilon'$ set to zero.
• Figure 5: Allowed regions from all solar neutrino data at 90%, 95%, 99%, and 3$\sigma$ C.L. for 2 d.o.f. in the plane of $\sin^2\theta_\textsc{sol}$ and $\Delta m^2_\textsc{sol}$. The regions delimited by the curves correspond to the BP00 SSM Bahcall:2000nu, whereas for the colored regions the BP04 SSM Bahcall:2004fg has been used. Also shown is $\Delta \chi^2$ as a function of $\sin^2\theta_\textsc{sol}$ and $\Delta m^2_\textsc{sol}$, minimized with respect to the undisplayed parameter. The labeled contours denote constant CC/NC ratio in the SNO experiment.