Neutrino spin evolution in presence of general external fields

The derivation of the quasiclassical Lorentz invariant neutrino spin evolution equation taking into account general types of neutrino non-derivative interactions with external fields is presented. We discuss the constraints on the characteristics of matter and neutrino under which this quasiclassical approach is valid. The application of the obtained equation for the case of the Standard Model neutrino interactions with moving and polarized background matter is considered.Comment: The form of the article has been sufficiently improve

A [SU(6)]4^4 FLAVOR MODEL WITHOUT MIRROR FERMIONS

We introduce a three family extension of the Pati-Salam model which is anomaly-free and contains in a single irreducible representation the known quarks and leptons without mirror fermions. Assuming that the breaking of the symmetry admits the implementation of the survival hypothesis, we calculate the mass scales using the renormalization group equation. Finally we show that the proton remains perturbatively stable.Comment: Z PHYS. C63, 339 (1994

One-loop flavor changing electromagnetic transitions

We discuss the effect of the external fermion masses in the flavor-changing radiative transitions of a heavy fermion (quark or lepton) to a lighter fermion at the one-loop level, and point out an often overlooked crucial difference in the sign of a charge factor between transitions of the down type $s\to d\gamma$ and the up type $c\to u\gamma$. We give formulas for the $F\to f\gamma$ effective vertex in various approximations and the exact formula for $t\to c\gamma$ and $\tau \to \mu \gamma$.Comment: LaTeX 16 pages + 4 postscript figures. Misprints corrected, some Comments adde

Matter effects and CP violating neutrino oscillations with non-decoupling heavy neutrinos

The evolution equation for active and sterile neutrinos propagating in general anisotropic or polarized background environment is found and solved for a special case when heavy neutrinos do not decouple, resulting in non-unitary mixing among light neutrino states. Then new CP violating neutrino oscillation effects appear. In contrast to the standard unitary neutrino oscillations these effects can be visible even for two flavour neutrino transitions and even if one of the elements of the neutrino mixing matrix is equal to zero. They do not necessarily vanish with $\delta m^{2} \to 0$ and they are different for various pairs of flavour neutrino transitions ($\nu_e \to \nu_\mu$), ($\nu_\mu \to \nu_\tau$), ($\nu_\tau \to \nu_e$). Neutrino oscillations in vacuum and Earth's matter are calculated for some fixed baseline experiments and a comparison between unitary and non-unitary oscillations are presented. It is shown, taking into account the present experimental constraints, that heavy neutrino states can affect CP and T asymmetries. This is especially true in the case of $\nu_\mu \to \nu_\tau$ oscillations.Comment: 18 pages, 6 fig

The seesaw mechanism at TeV scale in the 3-3-1 model with right-handed neutrinos

We implement the seesaw mechanism in the 3-3-1 model with right-handed neutrinos. This is accomplished by the introduction of a scalar sextet into the model and the spontaneous violation of the lepton number. We identify the Majoron as a singlet under $SU_L(2)\otimes U_Y(1)$ symmetry, which makes it safe under the current bounds imposed by electroweak data. The main result of this work is that the seesaw mechanism works already at TeV scale with the outcome that the right-handed neutrino masses lie in the electroweak scale, in the range from MeV to tens of GeV. This window provides a great opportunity to test their appearance at current detectors, though when we contrast our results with some previous analysis concerning detection sensitivity at LHC, we conclude that further work is needed in order to validate this search.Comment: about 13 pages, no figure

Model for Particle Masses, Flavor Mixing, and CP Violation Based on Spontaneously Broken Discrete Chiral Symmetry as the Origin of Families

We construct extensions of the standard model based on the hypothesis that the Higgs bosons also exhibit a family structure, and that the flavor weak eigenstates in the three families are distinguished by a discrete $Z_6$ chiral symmetry that is spontaneously broken by the Higgs sector. We study in detail at the tree level models with three Higgs doublets, and with six Higgs doublets comprising two weakly coupled sets of three. In a leading approximation of $S_3$ cyclic permutation symmetry the three Higgs model gives a ``democratic'' mass matrix of rank one, while the six Higgs model gives either a rank one mass matrix, or in the case when it spontaneously violates CP, a rank two mass matrix corresponding to nonzero second family masses. In both models, the CKM matrix is exactly unity in leading approximation. Allowing small explicit violations of cyclic permutation symmetry generates small first family masses in the six Higgs model, and first and second family masses in the three Higgs model, and gives a non-trivial CKM matrix in which the mixings of the first and second family quarks are naturally larger than mixings involving the third family. Complete numerical fits are given for both models, flavor changing neutral current constraints are discussed in detail, and the issues of unification of couplings and neutrino masses are addressed. On a technical level, our analysis uses the theory of circulant and retrocirculant matrices, the relevant parts of which are reviewed.Comment: Revtex, 59 pages including four tables at en

Thermal Background Corrections to the Neutrino Electromagnetic Vertex in Models with Charged Scalar Bosons

We calculate the correction to the neutrino electromagnetic vertex due to background of electrons in a large class of models, as the supersymmetric model with explicit breaking of R-parity, where charged scalar bosons couple to leptons and which are able to provide an astrophysically interesting value for the neutrino magnetic (electric) moment, $\mu_\nu\sim 10^{-12}\:\mu_B$. We show that the medium contribution to the chirality flipping magnetic (electric) dipole moment is not significant, however a new chirality flipping, but helicity conserving, term arises. It signals the presence of ${\cal CP}$ and ${\cal CPT}$ asymmetries in the medium and is associated to the longitudinal photon and therefore disappears in the vacuum. We estimate the contribution of this new term to the rate of the plasmon decay process $\gamma_{pl}\rightarrow \nu\nu$ in the core of degenerate stars, showing that it can be comparable with the contribution coming from the vacuum magnetic (dipole) moment. We also calculate the correction to the effective potential of a propagating neutrino in presence of a magnetic field due to a chirality preserving contribution to the diagonal magnetic moment from the medium. This contribution is identical for particles and antiparticles and so need not to vanish for Majorana neutrinos.Comment: DFPD 93/TH/75, SISSA 93/183/A preprint, 25 pages + 4 figures available by e-mail reques

Discrete symmetries, invisible axion and lepton number symmetry in an economic 3-3-1 model

We show that Peccei-Quinn and lepton number symmetries can be a natural outcome in a 3-3-1 model with right-handed neutrinos after imposing a Z_11 x Z_2 symmetry. This symmetry is suitably accommodated in this model when we augmented its spectrum by including merely one singlet scalar field. We work out the breaking of the Peccei-Quinn symmetry, yielding the axion, and study the phenomenological consequences. The main result of this work is that the solution to the strong CP problem can be implemented in a natural way, implying an invisible axion phenomenologically unconstrained, free of domain wall formation and constituting a good candidate for the cold dark matter.Comment: 17 pages, Revtex

Long Baseline Neutrino Physics with a Muon Storage Ring Neutrino Source

We examine the physics capabilities of known flavor neutrino beams from intense muon sources. We find that long-baseline neutrino experiments based on such beams can provide precise measurements of neutrino oscillation mass and mixing parameters. Furthermore, they can test whether the dominant atmospheric neutrino oscillations are \nu_\mu --> \nu_\tau and/or \nu_\mu --> \nu_s, determine the \nu_\mu --> \nu_e content of atmospheric neutrino oscillations, and measure \nu_e --> \nu_\tau appearance. Depending on the oscillation parameters, they may be able to detect Earth matter and CP violation effects and to determine the ordering of some of the mass eigenstates.Comment: 38 pages, Revtex with epsf.sty, 21 postscript figures. Minor text revisions, some new numbers in Tables II and II

Neutrino Propagation in a Strongly Magnetized Medium

We derive general expressions at the one-loop level for the coefficients of the covariant structure of the neutrino self-energy in the presence of a constant magnetic field. The neutrino energy spectrum and index of refraction are obtained for neutral and charged media in the strong-field limit ($M_{W}\gg \sqrt{B}\gg m_{e},T,\mu ,| \mathbf{p}|$) using the lowest Landau level approximation. The results found within the lowest Landau level approximation are numerically validated, summing in all Landau levels, for strong $B\gg T^{2}$ and weakly-strong $B \gtrsim T^{2}$ fields. The neutrino energy in leading order of the Fermi coupling constant is expressed as the sum of three terms: a kinetic-energy term, a term of interaction between the magnetic field and an induced neutrino magnetic moment, and a rest-energy term. The leading radiative correction to the kinetic-energy term depends linearly on the magnetic field strength and is independent of the chemical potential. The other two terms are only present in a charged medium. For strong and weakly-strong fields, it is found that the field-dependent correction to the neutrino energy in a neutral medium is much larger than the thermal one. Possible applications to cosmology and astrophysics are considered.Comment: 23 pages, 4 figures. Corrected misprints in reference