797 research outputs found
Pseudo-Dirac neutrinos from flavour dependent CP symmetry
Discrete residual symmetries and flavour dependent CP symmetries consistent
with them have been used to constrain neutrino mixing angles and CP violating
phases. We discuss here role of such CP symmetries in obtaining a pseudo-Dirac
neutrino which can provide a pair of neutrinos responsible for the solar
splitting. It is shown that if (a) Majorana neutrino matrix
is invariant under a discrete symmetry generated by ,
(b) CP symmetry transform as , and (c) and
obey consistency conditions , then two
of the neutrino masses are degenerate independent of specific forms of ,
and . Explicit examples of this result are discussed in the context
of groups which can also be used to constrain neutrino mixing
matrix . Degeneracy in two of the masses does not allow complete
determination of but it can also be fixed once the perturbations are
introduced. We consider explicit perturbations which break
symmetries but respect CP. These are shown to remove the degeneracy and provide
a predictive description of neutrino spectrum. In particular, a correlation
is obtained between the
atmospheric mixing angle and the CP violating phase
in terms of a group theoretically determined phase factor . Experimentally
interesting case ,
emerges for groups which predict purely imaginary . We present detailed
predictions of the allowed ranges of neutrino mixing angles, phases and the
lightest neutrino mass for three of the lowest groups with
.Comment: 17 pages, 4 figures; Minor modification, published versio
Generalized - symmetry and discrete subgroups of O(3)
The generalized - interchange symmetry in the leptonic mixing
matrix corresponds to the relations: with
. It predicts maximal atmospheric mixing and maximal Dirac CP
violation given . We show that the generalized -
symmetry can arise if the charged lepton and neutrino mass matrices are
invariant under specific residual symmetries contained in the finite discrete
subgroups of . The groups , and are the only such groups
which can entirely fix at the leading order. The neutrinos can be (a)
non-degenerate or (b) partially degenerate depending on the choice of their
residual symmetries. One obtains either vanishing or very large
in case of (a) while only can provide close to its
experimental value in the case (b). We provide an explicit model based on
and discuss a class of perturbations which can generate fully realistic
neutrino masses and mixing maintaining the generalized - symmetry in
. Our approach provides generalization of some of the ideas proposed earlier
in order to obtain the predictions, and .Comment: 18 page
Fermion Masses in SO(10) Models
We examine many SO(10) models for their viability or otherwise in explaining
all the fermion masses and mixing angles. This study is carried out for both
supersymmetric and non-supersymmetric models and with minimal ()
and non-minimal () Higgs content. Extensive numerical fits to
fermion masses and mixing are carried out in each case assuming dominance of
type-II or type-I seesaw mechanism. Required scale of the B-L breaking is
identified in each case. In supersymmetric case, several sets of data at the
GUT scale with or without inclusion of finite supersymmetric corrections are
used. All models studied provide quite good fits if the type-I seesaw mechanism
dominates while many fail if the type-II seesaw dominates. This can be traced
to the absence of the - unification at the GUT scale in these models.
The minimal non-supersymmetric model with type-I seesaw dominance gives
excellent fits. In the presence of a and an intermediate scale, the
model can also account for the gauge coupling unification making it potentially
interesting model for the complete unification. Structure of the Yukawa
coupling matrices obtained numerically in this specific case is shown to follow
from a very simple U(1) symmetry and a Froggatt-Nielsen singlet.Comment: 31 pages, 9 Tables, 4 figure
Quasi-degenerate neutrinos in SO(10)
Quark lepton universality inherent in grand unified theories based on
gauge group generically leads to hierarchical neutrino masses. We
propose a specific ansatz for the structure of Yukawa matrices in
models which differ from this generic expectations and lead to quasi degenerate
neutrinos through the type-I seesaw mechanism. Consistency of this ansatz is
demonstrated through a detailed fits to fermion masses and mixing angles all of
which can be explained with reasonable accuracy in a model which uses the Higgs
fields transforming as and representations of
. The proposed ansatz is shown to follow from an extended model based
on the three generations of the vector like fermions and an flavour
symmetry. Successful numerical fits are also discussed in earlier proposed
models which used combination of the type-I and type-II seesaw mechanisms for
obtaining quasi degenerate neutrinos. Large neutrino mixing angles emerge as a
consequence of neutrino mass degeneracy in both these cases.Comment: 12 page
Implications of partially degenerate neutrinos at a high scale in the light of KamLAND and WMAP
Electroweak radiative corrections can generate the neutrino (mass)
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 ) 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
Recommended from our members
Modelling electron interactions: a semi-rigorous method
We report total electron scattering cross sections (TCS) for SF6, SF5 CF3, and CF3I, molecules of interest to the plasma industry over the energy range from threshold to 2000 eV. We also report the total scattering cross sections for e-formaldehyde for which there are currently no theoretical or experimental results reported. The ionization cross sections for these targets are also estimated using the Deustch and Maerk formalism and are compared with Binary Encounter Bethe (BEB) data of Kim
- …