New mixing schemes for (3+1) neutrinos

Abstract

We propose new mixing schemes for (3+1) neutrinos which describe mixing among active-active and active-sterile neutrinos. The mixing matrix in these mixing schemes can be factored into a zeroth order flavor symmetric part and another part representing small perturbations needed for generating non-zero Ue3, nonmaximal θ23, CP violation and active-sterile mixing. We find interesting correlations amongst various neutrino mixing angles and, also, calculate the parameter space for various parameters. IntroductionThe discovery of massive neutrinos by Super-Kamiokande experiment [1] in the year 1998 has paved the way for new physics beyond the Standard Model (BSM) of particle physics. Various neutrino oscillation experiments in the last two decades have measured the three neutrino mixing angles and two (atmospheric |∆m 2 23 | and solar ∆m 2 21 ) mass splittings rather precisely. However, several anomalies at Short Base Line (SBL) neutrino experiments indicate eV scale mass splitting. These anomalies were first reported by LSND experiment [2] in their anti-neutrino flux measurements and, subsequently, confirmed by MiniBooNE experiment [3] in both the neutrino and antineutrino modes. The recent MiniBooNE data [4] also support these anomalies. In addition, reactor experiments [5] and gallium solar neutrino experiments [6] strongly support these anomalies. A possible explanation of these anomalies would require, at least, one eV scale mass eigenstate in the neutrino sector and the decay width of Z boson would require the fourth neutrino state to be sterile. The recent global analysis [7] of neutrino oscillations in the presence of eV-scale sterile neutrinos, supports the explanation of reactor anomaly in terms of sterile neutrino oscillations in 3+1 scenario but disfavour sterile neutrino explanation of LSND anomaly.Reactor neutrino data favour sterile neutrino oscillation with ∆m 2 41 ≈ 1.3eV 2 and |U e4 | ≈ 0.1 at the 3σ confidence level (CL) [7,8].The recent Planck data [9] limit the effective number of relativistic degrees of freedom to N ef f = 3.15 ± 0.23 (Planck TT+lowP+BAO) at 95% CL and the sum of neutrino masses to be m ν ≤ 0.23 eV at the same confidence level. This is consistent with the bound given by the standard model of cosmology: N ef f = 3.046.Although the cosmological bounds and latest Planck data disfavour the existence of eV scale sterile neutrinos, * sdev@associates.iucaa.in † raj.physics88@gmail.com ‡

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Jarlskog Determinant in Four Flavor Neutrino Oscillation Framework

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“…Current global fits [11][12][13] suggest |U i4 | ∼ 0.1, so in this paper we assume that U sterile 1 + O( √ ), which means that s i4 ∼ O( √ ) for i = 1, 2, 3. The small parameter is defined in Eq.…”