28 research outputs found
Radiative magnification of neutrino mixings and a natural explanation of the neutrino anomalies
We show that the neutrino mixing pattern with the large mixing required for
the atmospheric neutrino problem and the small mixing angle MSW solution for
the solar neutrino problem can be naturally generated through radiative
magnification, even though all the mixing angles at the seesaw scale may be
small. This can account for the neutrino anomalies as well as the CHOOZ
constraints in the context of quark-lepton unified theories, where the quark
and lepton mixing angles are expected to be similar in magnitude at the high
scale. We also indicate the 4 mixing scenarios for which this mechanism of
radiative magnification can provide a natural explanation.Comment: 14 pages RevTex, 2 eps figure
Perturbative and Nonperturbative Contributions to a Simple Model for Baryogenesis
Single field baryogenesis, a scenario for Dirac leptogenesis sourced by a
time-dependent scalar condensate, is studied. We compare the creation of the
charge asymmetry by the perturbative decay of the condensate with the
nonperturbative decay, a process of particle production commonly known in the
context of inflation as preheating. The nonperturbative channel dominates when
the coupling of the scalar field to leptons is sufficiently large.Comment: 11 pages, 3 figure
The solar LMA neutrino oscillation solution in the Zee model
We examine the neutrino mass matrix in the version of Zee model where both
Higgs doublets couple to the leptons. We show that in this case one can
accommodate the large mixing angle (LMA) MSW solution of the solar neutrino
problem, while avoiding maximal solar mixing and conflicts with constraints on
lepton family number-violating interactions. In the simplified scenario we
consider, we have the neutrino mass spectrum characterized by and , where is the solar mixing angle.Comment: 13 pages, LaTeX, no figures; misprints in Eq. (39) correcte
Zee Model Confronts SNO Data
We reexamine the solution of the minimal Zee model by comparing with the data
of the SNO experiment, and conclude that the model is strongly disfavored but
not yet excluded by the observations. Two extensions of the Zee model are
briefly discussed both of which introduce additional freedom and can
accommodate the data.Comment: 16 pages LaTeX including 7 figure
High scale mixing unification and large neutrino mixing angles
Starting with the hypothesis that quark and lepton mixings are identical at
or near the GUT scale, we show that the large solar and atmospheric neutrino
mixing angles together with the small reactor angle can be understood
purely as a result of renormalization group evolution. The only requirements
are that the three neutrinos must be quasi degenerate in mass and have same CP
parity. It predicts that the common Majorana mass for the neutrinos must be
larger than 0.1 eV making the idea testable in the currently planned or ongoing
experiments searching for neutrinoless-double-beta decay.Comment: 10 pages, eight figure, two tables; new material added; results
remain unchange
Dynamical CP Violation in the Early Universe
Following earlier ideas of Dolgov, we show that the asymmetrical dynamical
evolution of fields in the early Universe provides a new source for CP
violation. This can lead to baryogenesis without any additional CP-violating
interactions. The magnitude of this CP violation is time-dependent. In
particular, it vanishes (or is very small) in the late Universe after the
fields have relaxed (or are in their final approach) to their vacuum values. We
provide an explicit example in which our mechanism is realized.Comment: 9 pages, latex, 1 figure (enclosed). The idea of the previous version
was correct, but there were errors in its implementation. This has now been
corrected -- some text modified, references added. Also, one author has been
adde
Implications of a Massless Neutralino for Neutrino Physics
We consider the phenomenological implications of a soft SUSY breaking term BN
at the TeV scale (here B is the U(1)_Y gaugino and N is the right-handed
neutrino field). In models with a massless (or nearly massless) neutralino,
such a term will give rise through the see-saw mechanism to new contributions
to the mass matrix of the light neutrinos.
We treat the massless neutralino as an (almost) sterile neutrino and find
that its mass depends on the square of the soft SUSY breaking scale, with
interesting consequences for neutrino physics. We also show that, although it
requires fine-tuning, a massless neutralino in the MSSM or NMSSM is not
experimentally excluded. The implications of this scenario for neutrino physics
are discussed.Comment: 14 pages, latex, no figure
Power law enhancement of neutrino mixing angles in extra dimensions
We study the renormalization of the -type Majorana neutrino mass
operator in a scenario where there is a compactified extra dimension and the
fields involved correspond to only the standard model particles and their
Kaluza-Klein excitations. We observe that in a two flavour scenario, where one
of the neutrinos is necessarily , it is indeed possible to generate a
large mixing at 100 GeV starting from a very small mixing near the
ultra-violet cutoff 30 TeV. {\em En passant}, we also derive the Higgs
mass upper and lower limits from perturbative unitarity and stability of the
potential, respectively.Comment: Latex, 6 pages, one pslatex figure; v2: clarifying remarks added,
minor typos corrected, references updated, version to appear in Phys. Rev.
Revisiting pseudo-Dirac neutrinos
We study the pseudo-Dirac mixing of left and right-handed neutrinos in the
case where the Majorana masses M_L and M_R are small when compared with the
Dirac mass, M_D. The light Majorana masses could be generated by a
non-renormalizable operator reflecting effects of new physics at some high
energy scale. In this context, we obtain a simple model independent closed
bound for M_D. A phenomenologically consistent scenario is achieved with
M_L,M_R ~ 10^{-7} eV and M_D ~ 10^{-5}-10^{-4} eV. This precludes the
possibility of positive mass searches in the planned future experiments like
GENIUS or in tritium decay experiments. If on the other hand, GENIUS does
observe a positive signal for a Majorana mass \geq 10^{-3} eV, then with very
little fine tuning of neutrino parameters, the scale of new physics could be in
the TeV range, but pseudo-Dirac scenario in that case is excluded. We briefly
discuss the constraints from cosmology when a fraction of the dark matter is
composed of nearly degenerate neutrinos.Comment: 17 pages, no figures, references added, to be published in PL
Neutrino masses from operator mixing
We show that in theories that reduce, at the Fermi scale, to an extension of
the standard model with two doublets, there can be additional dimension five
operators giving rise to neutrino masses. In particular there exists a singlet
operator which can not generate neutrino masses at tree level but generates
them through operator mixing. Under the assumption that only this operator
appears at tree level we calculate the neutrino mass matrix. It has the Zee
mass matrix structure and leads naturally to bimaximal mixing. However, the
maximal mixing prediction for solar neutrinos is very sharp even when higher
order corrections are considered. To allow for deviations from maximal mixing a
fine tuning is needed in the neutrino mass matrix parameters. However, this
fine tuning relates the departure from maximal mixing in solar neutrino
oscillations with the neutrinoless double beta decay rate.Comment: 11 pages, 1 figure, revte