Abstract
The mixing of three active neutrino flavors is parameterized by the unitary PMNS matrix. If there are more than three neutrino flavors and if the extra generations are heavy iso-singlets, the effective 3times 3 mixing matrix for the three active neutrinos will be non-unitary. We have analyzed the latest T2K and NOnu A data with the hypothesis of non-unitary mixing of the active neutrinos. We found that the 2019 NOnu A data slightly (at sim 1, sigma CL) prefer the non-unitary mixing over unitary mixing. In fact, allowing the non-unitary mixing brings the NOnu A best-fit point in the sin ^2{theta _{23}}-delta _{mathrm {CP}} plane closer to the T2K best-fit point. The 2019 T2K data, on the other hand, cannot rule out any of the two mixing schemes. A combined analysis of the NOnu A and T2K 2019 data prefers the non-unitary mixing at 1, sigma CL. We derive constraints on the non-unitary mixing parameters using the best-fit to the combined NOnu A and T2K data. These constraints are weaker than previously found. The latest 2020 data from both the experiments prefer non-unitarity over unitary mixing at 1, sigma CL. The combined analysis prefers non-unitarity at 2, sigma CL. The stronger tension, which exists between the latest 2020 data of the two experiments, also gets reduced with non-unitary analysis.
Highlights
Neutrino oscillation phenomena has been well established by the solar [1,2], atmospheric [3] and reactor [4,5,6] neutrino experiments
The angle θ12 and mass-squared difference 21 were measured in the a e-mail: ushakr@uj.ac.za solar neutrino experiments [1,2], | 31| was measured in the accelerator neutrino experiment MINOS [7], and θ13 was measured in the reactor neutrino experiments [4,5,6]
If extra neutrino generations exist as iso-singlet neutral heavy leptons (NHL), in the minimal extension of the standard model, they would not take part in neutrino oscillations
Summary
Neutrino oscillation phenomena has been well established by the solar [1,2], atmospheric [3] and reactor [4,5,6] neutrino experiments. On the other hand the NOνA best-fit point is at sin θ23 = 0.56+−00..0043, and δCP/π = 0−+01..43 for normal hierarchy. There is a visible difference between the δCP values at the NOνA and T2K best-fit points. As per the latest analysis, the best-fit point for NOνA (T2K) is sin θ23 = 0.57 (0.528) and δCP = 0.82π (−1.6π ). Apart from the unknowns in the three flavor neutrino mixing, there are anomalies from the short baseline experiments, which cannot be accounted for in the three flavor oscillation formalism.
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