Model-Independent Constraints on Non-Unitary Neutrino Mixing from High-Precision Long-Baseline Experiments

Abstract

Our knowledge on the active three-neutrino mixing angles (θ 12 , θ 13 , and θ 23 ) and the Dirac CP phase δ CP is becoming accurate day-by-day enabling us to test the unitarity of the leptonic mixing matrix with utmost precision. Future high-precision longbaseline experiments are going to play an important role in this direction. In this work, we study the impact of possible non-unitary neutrino mixing (NUNM) in the context of nextgeneration long-baseline experiments DUNE and T2HKK/JD+KD having one detector in Japan (T2HK/JD) and a second detector in Korea (KD). We estimate the sensitivities of these setups to place direct, model-independent, and competitive constraints on various NUNM parameters. We demonstrate the possible correlations between the NUNM parameters and the oscillations parameters θ 23 and δ CP . Our numerical results, supported by simple approximate analytical expressions of the oscillation probabilities in matter, reveal that JD+KD has better sensitivities for |α 21 | and α 22 as compared to DUNE, due to its larger statistics in the appearance channel and less systematic uncertainties in the disappearance channel, respectively. For |α 31 |, |α 32 |, and α 33 , DUNE gives better constraints as compared to JD+KD, due to its larger matter effect and wider neutrino energy spectrum. For α 11 , both DUNE and JD+KD give similar bounds. We also show how much the bounds on the NUNM parameters can be improved by combining the prospective data from DUNE and JD+KD setups. Due to the presence of zero-distance effects, the data from near detectors in both DUNE and JD+KD experiments, can further improve the limits on |α 21 | considerably, while giving slightly better constraints for α 11 and α 22 . Finally, we observe that the ν τ appearance sample in DUNE can improve the constraints on |α 32 | and α 33 .

Tau neutrinos in the next decade: from GeV to EeV

“…While the electron and muon rows of the leptonic mixing matrix are well constrained due to the large statistics of the electron neutrino disappearances samples from reactor experiments and muon neutrino disappearance data from long baseline experiments [74,75,[84][85][86] the tau row is currently comparably worse constrained and allows for sizable deviations from unitarity. In order to thoroughly probe the standard neutrino paradigm, all 9 unitarity conditions, following from UU † = 1, need to be tested.…”

Constraining Lorentz Invariance Violation with Next-Generation Long-Baseline Experiments

“…Apart from measuring the standard oscillation parameters with high precision, the long-baseline experiments will also search for new physics beyond the Standard Model (BSM) 1 through neutrino oscillation, namely, eV-scale sterile neutrino [35][36][37][38][39][40], neutrino non-standard interactions [41,42], non-unitary neutrino mixing [43,44], long-range interactions [45], neutrino decay [46,47], and Lorentz Invariance Violation (LIV) [48][49][50]. In this work, we mainly focus on LIV.…”

Precision measurements and tau neutrino physics in a future accelerator neutrino experiment

“…The implications of non-unitarity parameters in neutrino oscillation probabilities have been discussed extensively in the literature, see e.g [54][55][56][57][58][59]…”