Radiatively Generated νe\nu_e Oscillations: General Analysis, Textures and Models

We study the consequences of assuming that the mass scale $\Delta_{odot}$ corresponding to the solar neutrino oscillations and mixing angle $U_{e3}$ corresponding to the electron neutrino oscillation at CHOOZ are radiatively generated through the standard electroweak gauge interactions. All the leptonic mass matrices having zero $\Delta_{odot}$ and $U_{e3}$ at a high scale lead to a unique low energy value for the $\Delta_{odot}$ which is determined by the (known) size of the radiative corrections, solar and the atmospheric mixing angle and the Majorana mass of the neutrino observed in neutrinoless double beta decay. This prediction leads to the following consequences: ($i$) The MSSM radiative corrections generate only the dark side of the solar neutrino solutions. ($ii$) The inverted mass hierarchy ($m,-m,0$) at the high scale fails in generating the LMA solution but it can lead to the LOW or vacuum solutions. ($iii$) The $\Delta_{odot}$ generated in models with maximal solar mixing at a high scale is zero to the lowest order in the radiative parameter. It tends to get suppressed as a result of this and lies in the vacuum region. We discuss specific textures which can lead to the LMA solution in the present framework and provide a gauge theoretical realization of this in the context of the seesaw model.Comment: 19 pages, LATE

Fast Neutrino Decay in the Minimal Seesaw Model

Neutrino decay in the minimal seesaw model containing three right handed neutrinos and a complex $SU(2)\times U(1)$ singlet Higgs in addition to the standard model fields is considered. A global horizontal symmetry $U(1)_H$ is imposed, which on spontaneous breaking gives rise to a Goldstone boson. This symmetry is chosen in a way that makes a) the contribution of heavy ($\leq$ MeV) majorana neutrinos to the neutrinoless double beta decay amplitude vanish and b) allows the heavy neutrino to decay to a lighter neutrino and the Goldstone boson. It is shown that this decay can occur at a rate much faster than in the original Majoron model even if one does not introduce any additional Higgs fields as is done in the literature. Possibility of describing the 17 keV neutrino in this minimal seesaw model is investigated. While most of the cosmological and astrophysical constraints on the 17 keV neutrino can be satisfied in this model, the laboratory limits coming from the neutrino oscillations cannot be easily met. An extension which removes this inadequacy and offers a consistent description of the 17 keV neutrino is discussed.Comment: 16 pages, PRL-TH/92-1

Predictive Framework with a Pair of Degenerate Neutrinos at a high scale

Radiative generation of the solar scale $\Delta_{\odot}$ is discussed in the presence of leptonic CP violation. We assume that both the solar scale and $U_{e3}$ are zero at a high scale and the weak radiative corrections generate them. It is shown that all leptonic mass matrices satisfying these requirements lead to a unique prediction $\Delta_{\odot} \cos 2\theta_{\odot}\approx 4 \delta_\tau \sin^2 \theta_A |m_{ee}|^2$ for the solar scale in terms of the radiative correction parameter $\delta_\tau$, the physical solar (atmospheric) mixing angles $\theta_{odot} (\theta_A)$ and the Majorana neutrino mass $m_{ee}$ probed in neutrinoless double beta decay. This relation is independent of the mixing matrix and CP-violating phases at the high scale. The presence of CP-violating phases leads to dilution in the solar mixing angle defined at the high scale. Because of this, bi-maximal mixing pattern at the high energy leads to large but non-maximal solar mixing in the low-energy theory. An illustrative model with this feature is discussed.Comment: 15 pages, including a postscript figur

Implications of partially degenerate neutrinos at a high scale in the light of KamLAND and WMAP

Electroweak radiative corrections can generate the neutrino (mass)$^2$ difference required for the large mixing angle solution (LMA) to the solar neutrino problem if two of the neutrinos are assumed degenerate at high energy. We test this possibility with the existing experimental knowledge of the low energy neutrino mass and mixing parameters. We derive restrictions on ranges of the high scale mixing matrix elements and obtain predictions for the low energy parameters required in order to get the LMA solution of the solar neutrino problem picked out by KamLAND. We find that in the case of standard model this is achieved only when the (degenerate) neutrino masses lie in the range (0.7-2) \eV which is at odds with the cosmological limit m_{\nu}<0.23 \eV (at $95$) established recently using WMAP results. Thus SM radiative corrections cannot easily generate the LMA solution in this scenario. However, the LMA solution is possible in case of the MSSM electroweak corrections with (almost) degenerate spectrum or with inverted mass hierarchy for limited ranges in the high scale parameters.Comment: 15 pages, LATEX includes five postscript figure

Breaking of B-L in superstring inspired E6 model

In the framework of the superstring inspired E6 model, low-energy extensions of the standard model compatible with leptogenesis are considered and masses of right-handed neutrinos in two scenarios allowed by long-lived protons are discussed. The presence of two additional generations allows breaking of B-L without generating nonzero vacuum expectation values of right-handed sneutrinos of the three known generations. After the symmetry breaking, right-handed neutrinos acquire Majorana masses of order of 10^11 GeV. Within the framework of a simple discrete symmetry, assumptions made to provide a large mass of right-handed neutrinos are shown to be self-consistent. Supersymmetric structure of the theory ensures that large corrections, associated with the presence of a (super)heavy gauge field, cancel out.Comment: 18 pages, 6 tables, axodraw use

Phenomenology of Pseudo Dirac Neutrinos

We formulate general conditions on $3\times 3$ neutrino mass matrices under which a degenerate pair of neutrinos at a high scale would split at low scale by radiative corrections involving only the standard model fields. This generalizes the original observations of Wolfenstein on pseudo Dirac neutrinos to three generations. A specific model involving partially broken discrete symmetry and solving the solar and atmospheric anomalies is proposed. The symmetry pattern of the model naturally generates two large angles one of which can account for the large angle MSW solution to the solar neutrino problem.Comment: 15 pages LATE

Neutrino Anomalies in an Extended Zee Model

We discuss an extended $SU(2)\times U(1)$ model which naturally leads to mass scales and mixing angles relevant for understanding both the solar and atmospheric neutrino anomalies. No right-handed neutrinos are introduced in the model.The model uses a softly broken $L_e-L_{\mu}-L_{\tau}$ symmetry. Neutrino masses arise only at the loop level. The one-loop neutrino masses which arise as in the Zee model solve the atmospheric neutrino anomaly while breaking of $L_e-L_{\mu}-L_{\tau}$ generates at two-loop order a mass splitting needed for the vacuum solution of the solar neutrino problem. A somewhat different model is possible which accommodates the large-angle MSW resolution of the solar neutrino problem.Comment: 11 pages including 2 figures; a reference added and text changed accordingl