We present the results of a global analysis of the neutrino oscillation data available as of fall 2018 in the framework of three massive mixed neutrinos with the goal at determining the ranges of allowed values for the six relevant parameters. We describe the complementarity and quantify the tensions among the results of the different data samples contributing to the determination of each parameter. We also show how those vary when combining our global likelihood with the χ2 map provided by Super-Kamiokande for their atmospheric neutrino data analysis in the same framework. The best fit of the analysis is for the normal mass ordering with inverted ordering being disfavoured with a Δχ2 = 4.7 (9.3) without (with) SK-atm. We find a preference for the second octant of θ23, disfavouring the first octant with Δχ2 = 4.4 (6.0) without (with) SK-atm. The best fit for the complex phase is δCP = 215° with CP conservation being allowed at Δχ2 = 1.5 (1.8). As a byproduct we quantify the correlated ranges for the laboratory observables sensitive to the absolute neutrino mass scale in beta decay, $$ {m}_{\nu_e} $$
 , and neutrino-less double beta decay, mee, and the total mass of the neutrinos, Σ, which is most relevant in Cosmology.

/pdf/global-analysis-of-three-flavour-neutrino-oscillations-2l1eple4qn.pdf

Global analysis of three-flavour neutrino oscillations: synergies and tensions in the determination of θ 23 , δ CP , and the mass ordering

We perform a combined fit to global neutrino oscillation data available as of fall 2016 in the scenario of three-neutrino oscillations and present updated allowed ranges of the six oscillation parameters. We discuss the differences arising between the consistent combination of the data samples from accelerator and reactor experiments compared to partial combinations. We quantify the confidence in the determination of the less precisely known parameters θ
 23, δ
 CP, and the neutrino mass ordering by performing a Monte Carlo study of the long baseline accelerator and reactor data. We find that the sensitivity to the mass ordering and the θ
 23 octant is below 1σ. Maximal θ
 23 mixing is allowed at slightly more than 90% CL. The best fit for the CP violating phase is around 270°, CP conservation is allowed at slightly above 1σ, and values of δ
 CP ≃ 90° are disfavored at around 99% CL for normal ordering and higher CL for inverted ordering.

https://link.springer.com/content/pdf/10.1007/JHEP01(2017)087.pdf

Updated fit to three neutrino mixing: exploring the accelerator-reactor complementarity

We present a comprehensive overview of an extension of the Standard Model that contains three right-handed (sterile) neutrinos with masses below the electroweak scale [the Neutrino Minimal Standard Model (νMSM)]. We consider the history of the Universe from the inflationary era through today and demonstrate that most of the observed phenomena beyond the Standard Model can be explained within the framework of this model. We review the mechanism of baryon asymmetry of the Universe in the νMSM and discuss a dark matter candidate that can be warm or cold and that satisfies all existing constraints. From the viewpoint of particle physics, the model provides an explanation for neutrino flavor oscillations. Verification of the νMSM is possible with existing experimental techniques.

https://www.annualreviews.org/doi/pdf/10.1146/annurev.nucl.010909.083654

The Role of Sterile Neutrinos in Cosmology and Astrophysics

Our herein described combined analysis of the latest neutrino oscillation data presented at the Neutrino2020 conference shows that previous hints for the neutrino mass ordering have significantly decreased, and normal ordering (NO) is favored only at the 1.6σ level. Combined with the χ2 map provided by Super-Kamiokande for their atmospheric neutrino data analysis the hint for NO is at 2.7σ. The CP conserving value δCP = 180° is within 0.6σ of the global best fit point. Only if we restrict to inverted mass ordering, CP violation is favored at the ∼ 3σ level. We discuss the origin of these results — which are driven by the new data from the T2K and NOvA long-baseline experiments —, and the relevance of the LBL-reactor oscillation frequency complementarity. The previous 2.2σ tension in ∆m221 preferred by KamLAND and solar experiments is also reduced to the 1.1σ level after the inclusion of the latest Super-Kamiokande solar neutrino results. Finally we present updated allowed ranges for the oscillation parameters and for the leptonic Jarlskog determinant from the global analysis.

/pdf/the-fate-of-hints-updated-global-analysis-of-three-flavor-354eww4t2d.pdf

The fate of hints: updated global analysis of three-flavor neutrino oscillations

We present a global analysis of solar, atmospheric, reactor and accelerator neutrino data in the framework of three-neutrino oscillations based on data available in summer 2014. We provide the allowed ranges of the six oscillation parameters and show that their determination is stable with respect to uncertainties related to reactor neutrino and solar neutrino flux predictions. We find that the maximal possible value of the Jarlskog invariant in the lepton sector is 0.033 ±0.010 (±0.027) at the 1σ (3σ) level and we use leptonic unitarity triangles to illustrate the ability of global oscillation data to obtain information on CP violation. We discuss “tendencies and tensions” of the global fit related to the octant of θ
 23 as well as the CP violating phase δ
 CP. The favored values of δ
 CP are around 3π/2 while values around π/2 are disfavored at about Δχ2 ≃6. We comment on the non-trivial task to assign a confidence level to this Δχ
 2 value by performing a Monte Carlo study of T2K data.

https://link.springer.com/content/pdf/10.1007/JHEP11%282014%29052.pdf

Updated fit to three neutrino mixing: status of leptonic CP violation

Matter can enhance neutrino oscillations (increase the mixing parameter sin/sup 2/ 2theta/sub m/). For small mixing angles in vacuum the enhancement displays a resonance behavior in the neutrino energies or the density of the medium. This resonance effect is important for solar neutrinos in a wide range of oscillation parameters ..delta..m/sup 2/ = 10/sup -4/--10/sup -8/ eV/sup 2/ and sin/sup 2/ 2theta>10/sup -4/. It leads to a strong suppression of the neutrino flux even for small sin/sup 2/ 2theta.

S.P. Mikheev

Papers

Resonance enhancement of oscillations in matter and solar neutrino spectroscopy