https://doi.org/10.1140/epjc/s10052-021-09227-0
Regular Article - Theoretical Physics
Searching for non-unitary neutrino oscillations in the present T2K and NO
A data
1
Centre for Astro-Particle Physics (CAPP) and Department of Physics, University of Johannesburg, PO Box 524, 2006, Auckland Park, South Africa
2
Instituto de Física Teórica–Universidade Estadual Paulista (UNESP), R. Dr. Bento Teobaldo Ferraz 271, Barra Funda, 01140-070, São Paulo, SP, Brazil
3
Tsung-Dao Lee Institute and School of Physics and Astronomy, Shanghai Jiao Tong University, 200240, Shanghai, China
Received:
15
February
2021
Accepted:
10
May
2021
Published online:
24
May
2021
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 
mixing matrix for the three active neutrinos will be non-unitary. We have analyzed the latest T2K and NOA data with the hypothesis of non-unitary mixing of the active neutrinos. We found that the 2019 NOA data slightly (at 
CL) prefer the non-unitary mixing over unitary mixing. In fact, allowing the non-unitary mixing brings the NOA best-fit point in the 
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 NOA and T2K 2019 data prefers the non-unitary mixing at 
CL. We derive constraints on the non-unitary mixing parameters using the best-fit to the combined NOA 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 CL. The combined analysis prefers non-unitarity at 
CL. The stronger tension, which exists between the latest 2020 data of the two experiments, also gets reduced with non-unitary analysis.
© The Author(s) 2021
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