7,938 research outputs found
A See-Saw Model for Atmospheric and Solar Neutrino Oscillations
We have constructed an explicit see-saw model containing two singlet neutrinos, one carrying a gauge charge with an intermediate mass scale of GeV along with a sterile one near the GUT (grand unification theory) scale of GeV. With these mass scales and a reasonable range of Yukawa couplings, the model can naturally account for the near-maximal mixing of atmospheric neutrino oscillations and the small mixing matter-enhanced oscillation solution to the solar neutrino deficit
Low-Energy Thermal Leptogenesis in an Extended NMSSM Model
Thermal leptogenesis in the canonical seesaw model in supersymmetry suffers
from the incompatibility of a generic lower bound on the mass scale of the
lightest right-handed neutrino and the upper bound on the reheating temperature
of the Universe after inflation. This is resolved by adding an extra singlet
superfield, with a discrete symmetry, to the NMSSM (Next to Minimal
Supersymmetric Standard Model). This generic mechanism is applicable to any
supersymmetric model for lowering the scale of leptogenesis.Comment: 16 pages, revtex, 9 eps figure
A Model for Neutrino Masses and Dark Matter
We propose a model for neutrino masses that simultaneously results in a new
dark matter candidate, the right-handed neutrino. We derive the dark matter
abundance in this model, show how the hierarchy of neutrino masses is obtained,
and verify that the model is compatible with existing experimental results. The
model provides an economical method of unifying two seemingly separate puzzles
in contemporary particle physics and cosmology.Comment: 4 pages, submitted to PR
Right-Handed Sector Leptogenesis
Instead of creating the observed baryon asymmetry of the universe by the
decay of right-handed (RH) neutrinos to left-handed leptons, we propose to
generate it dominantly by the decay of the RH neutrinos to RH leptons. This
mechanism turns out to be successful in large regions of parameter space. It
may work, in particular, at a scale as low as ~TeV, with no need to
invoke quasi-degenerate RH neutrino masses to resonantly enhance the asymmetry.
Such a possibility can be probed experimentally by the observation at colliders
of a singlet charged Higgs particle and of RH neutrinos. Other mechanisms which
may lead to successful leptogenesis from the RH lepton sector interactions are
also briefly presented. The incorporation of these scenarios in left-right
symmetric and unified models is discussed.Comment: 14 pages, latex, axodraw; minor clarifications and references added,
extended discussion of the signatures at collider
Stability of Neutrino Mass Degeneracy
Two neutrinos of Majorana masses with mixing angle are
unstable against radiative corrections in the limit , but are stable
for (i.e. opposite CP eigenstates) with which
corresponds to an additional symmetry.Comment: 7 pages, no figure, one reference adde
Degenerate Dirac Neutrinos
A simple extension of the standard model is proposed in which all the three
generations of neutrinos are Dirac particles and are naturally light. We then
assume that the neutrino mass matrix is diagonal and degenerate, with a few eV
mass to solve the dark matter problem. The self energy radiative corrections,
however, remove this degeneracy and allow mixing of these neutrinos. The
electroweak radiative corrections then predict a lower bound on the mass difference which solves the solar neutrino problem through MSW
mechanism and also predict a lower bound on the mass
difference which is just enough to explain the atmospheric neutrino problem as
reported by super Kamiokande.Comment: 11 pages latex fil
See-saw mechanism and four light neutrino state
A formal proof is given that in a see-saw type neutrino mass matrix with only
two neutrino mass scales () and the maximal rank of , we
can not get a fourth light sterile neutrino.Comment: 5 page
Leptogenesis with Heavy Majorana Neutrinos Reexamined
The mass term for Majorana neutrinos explicitly violates lepton number.
Several authors have used this fact to create a lepton asymmetry in the
universe by considering CP violating effects in the one loop self-energy
correction for the decaying heavy Majorana neutrino. We compare and comment on
the different approaches used to calculate the lepton asymmetry including those
using an effective Hamiltonian and resummed propagators. We also recalculate
the asymmetry in the small mass difference limit.Comment: 16 pages, LaTex, 1 figure included. 2 footnotes and 1 reference adde
A texture of neutrino mass matrix in view of recent neutrino experimental results
In view of recent neutrino experimental results such as SNO, Super-Kamiokande
(SK), CHOOZ and neutrinoless double beta decay , we
consider a texture of neutrino mass matrix which contains three parameters in
order to explain those neutrino experimental results. We have first fitted
parameters in a model independent way with solar and atmospheric neutrino mass
squared differences and solar neutrino mixing angle which satisfy LMA solution.
The maximal value of atmospheric neutrino mixing angle comes out naturally in
the present texture. Most interestingly, fitted parameters of the neutrino mass
matrix considered here also marginally satisfy recent limit on effective
Majorana neutrino mass obtained from neutrinoless double beta decay experiment.
We further demonstrate an explicit model which gives rise to the texture
investigated by considering an gauge group with two
extra real scalar singlets and discrete symmetry. Majorana
neutrino masses are generated through higher dimensional operators at the scale
. We have estimated the scales at which singlets get VEV's and M by
comparing with the best fitted results obtained in the present work.Comment: Journal Ref.: Phys. Rev. D66, 053004 (2002
Minimal See-Saw Model for Atmospheric and Solar Neutrino Oscillations
We present a minimal see-saw model based on an extension of the standard
model (SM) which includes an additional U(1), with gauge charge . Requirement of anomaly cancellation implies the
existence of two right-handed singlet neutrinos, carrying this gauge charge,
which have normal Dirac couplings to and but suppressed
ones to . Assuming the U(1) symmetry breaking scale to be
10~GeV, this model can naturally account for the large (small) mixing
solutions to the atmospheric (solar) neutrino oscillations.Comment: 14 pages, latex, no figure
- âŠ