An apprach to generate large and small lep- tonic mixing angles

We take up the point of view that Yukawa couplings can be either 0 or 1, and the mass patterns of fermions are generated purely from the structure of the Yukawa matrices. We utilize such neutrino as well as charged leptonic textures which lead to (maximal) mixing angles of π/4 in each sector for relevant transitions. The combined leptonic CKM mixing angles are π/4 ± π/4 which lead to very small sin 2Θ relevant to solar neutrino and LSND experiments. We propose that on the other hand the absence of the charged leptonic partner of the sterile neutrino maintains the angle π/4 from the neutrino sector for the transition νμ ↔ νs and hence atmospheric neutrino anomaly is explained through maximal mixing. Recent ‘evidence’ of neutrino mass detected at Super Kamiokande experiments[1] and announced at the neutrino-98 conference[2] has sparred new enthusiasm for the studies of physics beyond standard model, particularly of the neutrino mass matrices in the leptonic sector. In the Standard model (SM) neutrinos are massless and being based on gauge symmetries SM treat all the generations of matter identically though it is well-known that fermion masses differentiate among generations. If neutrinos have masses they are not expected to be generation blind at the same token. Neutrino oscillations establish this. The neutrinos should not only be massive, but also different generations 1 must differ in masses for them to oscillate into one another. At a deeper level (in a gauge theory) we relate the masses to the Yukawa matrices or textures describing the interactions of fermionic matter with scalars whereas their forms are left unconstrained by gauge symmetries. Even-though grand unified gauge symmetries may relate the Yukawa interactions of the quarks to those of leptons[3, 4] the strengths of the interactions still remain arbitrary. Thus, it is imperative to study forms of textures as physics beyond standard model. Hence, we study simple symmetry properties of leptonic Yukawa textures themselves in the generation space which may describe the patterns of masses (eigenvalues) and mixing angles (eigenvectors) suggested by a variety of experimental measurements. For example, experimental inputs are provided by laboratory experiments as LSND neutrino oscillations experiments and neutrino-less double beta decay experiments, terestrial experiments such solar and atmospheric neutrino experiments as well as astrophysical observations such as nonluminous ‘dark matter’ and the abundance of He in metal-poor blue compact galaxies. Even if the preliminary data from Karmen experiments[5] have failed to reproduce the LSND results; we assume that in course of time LSND observations will be well established which indicates that νμ(νμ) is oscilatting to νe(νe) with ∆m 2 eμ in the electron volt range. In this case solar neutrino deficit can be caused by νe ↔ ντ or νe ↔ νs oscillations with ∆m approximately 10−5 eV; whereas the atmospheric neutrino anomaly can be explained by νμ ↔ ντ or νμ ↔ νs oscillations, with ∆m approximately 10−3 eV. The pattern which emerges as a result This can be avoided if the masses of the quarks and leptons arize from different scalars.