New model for the neutrino mass matrix

I suggest a model based on a softly broken symmetry L_e - L_mu - L_tau and on Babu's mechanism for two-loops radiative generation of the neutrino masses. The model predicts that one of the physical neutrinos (nu_3) is massless and that its component along the nu_e direction (U_e3) is zero. Moreover, if the soft-breaking term is assumed to be very small, then the vacuum oscillations of nu_e have almost maximal amplitude and solve the solar-neutrino problem. New scalars are predicted in the 10 TeV energy range, and a breakdown of e-mu-tau universality should not be far from existing experimental bounds.Comment: 7 pages including 3 figure

A simple connection between neutrino oscillation and leptogenesis

The usual see-saw formula is modified by the presence of two Higgs triplets in left-right symmetric theories. The contribution from the left-handed Higgs triplet to the see-saw formula can dominate over the conventional one when the neutrino Dirac mass matrix is identified with the charged lepton or down quark mass matrix. In this case an analytic calculation of the lepton asymmetry, generated by the decay of the lightest right-handed Majorana neutrino, is possible. For typical parameters, the out-of-equilibrium condition for the decay is automatically fulfilled. The baryon asymmetry has the correct order of magnitude, as long as the lightest mass eigenstate is not much lighter then 10^{-6} to 10^{-8} eV, depending on the solution of the solar neutrino problem. A sizable signal in neutrinoless double beta decay can be expected, as long as the smallest mass eigenstate is not much lighter than 10^{-3} eV and the Dirac mass matrix is identified with the charged lepton mass matrix.Comment: 16 pages, 3 figures. One paragraph and some references added, typos correcte

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

Introduction to Models of Neutrino Masses and Mixings

This review contains an introduction to models of neutrino masses for non-experts. Topics discussed are (i) different types of neutrino masses (ii) structure of neutrino masses and mixing needed to understand neutrino oscillation results (iii) mechanisms to generate neutrino masses in gauge theories and (iv) discussion of generic scenarios proposed to realize the required neutrino mass structures

Lepton Masses in a Minimal Model with Triplet Higgs Bosons and S3S_3 Flavor Symmetry

Viable neutrino and charged lepton masses and mixings are obtained by imposing a $S_3 \times Z_4 \times Z_3$ flavor symmetry in a model with a few additional Higgs. We use two $SU(2)_L$ triplet Higgs which are arranged as a doublet of $S_3$, and standard model singlet Higgs which are also put as doublets of $S_3$. We break the $S_3$ symmetry in this minimal model by giving vacuum expectation values (VEV) to the additional Higgs fields. Dictated by the minimum condition for the scalar potential, we obtain certain VEV alignments which allow us to maintain $\mu-\tau$ symmetry in the neutrino sector, while breaking it maximally for the charged leptons. This helps us to simultaneously explain the hierarchical charged lepton masses, and the neutrino masses and mixings. In particular, we obtain maximal $\theta_{23}$ and zero $\theta_{13}$. We allow for a mild breaking of the $\mu-\tau$ symmetry for the neutrinos and study the phenomenology. We give predictions for $\theta_{13}$ and the CP violating Jarlskog invariant $J_{CP}$, as a function of the $\mu-\tau$ symmetry breaking parameter. We also discuss possible collider signatures and phenomenology associated with lepton flavor violating processes.Comment: 29 pages, 5 figures. Version to be appeared in PRD. Phenomenology of Lepton flavor violation and possible collider signatures of this model have been include

Minimal flavour violations and tree level FCNC

Consequences of a specific class of two Higgs doublet models in which the Higgs induced tree level flavour changing neutral currents (FCNC) display minimal flavour violation (MFV) are considered. These FCNC are fixed in terms of the CKM matrix elements and the down quark masses. The minimal model in this category with only two Higgs doublets has no extra CP violating phases but such a phase can be induced by adding a complex singlet. Many of the theoretical predictions are similar to other MFV scenario. The FCNC contribute significantly to $B$ meson mixing and CP violation. Detailed numerical analysis to determine the allowed Higgs contributions to neutral meson mixings and the CKM parameters $\bar{\rho},\bar{\eta}$ in their presence is presented. The Higgs induced phase in the $B^0_{d,s}-\bar{B}^0_{d,s}$ transition amplitude $M_{12}^{d,s}$ is predicted to be equal for the $B_d$ and the $B_s$ systems. There is a strong correlation between phases in $M_{12}^{d,s}$ and $|V_{ub}|$. A measurable CP violating phase $\phi_s=-0.18\pm 0.08$ is predicted on the basis of the observed phase $\phi_d$ in the $B_d$ system if $|V_{ub}|$ is large and close to its value determined from the inclusive b decays.Comment: 15 pages, two postscript figure