62 research outputs found
Lifting a Realistic SO(10) Grand Unified Model to Five Dimensions
It has been shown recently that the problem of rapid proton decay induced by
dimension five operators arising from the exchange of colored Higgsinos can be
simply avoided in grand unified models where a fifth spatial dimension is
compactified on an orbifold. Here we demonstrate that this idea can be used to
solve the Higgsino-mediated proton decay problem in any realistic SO(10) model
by lifting that model to five dimensions. A particular SO(10) model that has
been proposed to explain the pattern of quark and lepton masses and mixings is
used as an example. The idea is to break the SO(10) down to the Pati-Salam
symmetry by the orbifold boundary conditions. The entire four-dimensional
SO(10) model is placed on the physical SO(10) brane except for the gauge
fields, the 45 and a single 10 of Higgs fields, which are placed in the
five-dimensional bulk. The structure of the Higgs superpotential can be
somewhat simplified in doing so, while the Yukawa superpotential and mass
matrices derived from it remain essentially unaltered.Comment: 17 pages, version to be published in Phys. Rev. D with expanded
discussion of the suppression of dim-5 proton decay operator
Implications of a Minimal SO(10) Higgs Structure
A minimal SO(10) Higgs structure involving a single adjoint field along with
spinors, vectors and singlets has been shown to break the SO(10) gauge symmetry
to the standard model while stabilizing the F-flat directions and solving the
doublet-triplet splitting problem naturally. With this minimal set of Higgs
fields, we show how to construct quark and lepton mass matrices which explain
well the many features of the observed spectrum, including the Georgi-Jarlskog
mass relations. A large mixing of the muon- and tau-neutrinos results naturally
as observed in the atmospheric neutrino data. A particular model relying on a
family symmetry has been constructed which realizes the desired mass matrices.Comment: 10 pages, REVTEX, contribution submitted to NEUTRINO 98 Conferenc
Fermion masses in SO(10) with a single adjoint Higgs field
It has recently been shown how to break SO(10) down to the Standard Model in
a realistic way with only one adjoint Higgs. The expectation value of this
adjoint must point in the B-L direction. This has consequences for the possible
form of the quark and lepton mass matrices. These consequences are explored in
this paper, and it is found that one is naturally led to consider a particular
form for the masses of the heavier generations. This form implies typically
that there should be large (nearly maximal) mixing of the mu- and
tau-neutrinos. An explanation that does not involve large tan beta also emerges
for the fact that b and tau are light compared to the top quark.Comment: 20 pages, LaTeX, clarification of statements about multiple adjoint
Higgs fields in the context of superstring theor
Family Unification with SO(10)
Unification based on the group SO(10)^3 \times S_3 is studied. Each family
has its own SO(10) group, and the S_3 permutes the three families and SO(10)
factors. This is the maximal local symmetry for the known fermions. Family
unification is achieved in the sense that all known fermions are in a single
irreducible multiplet of the symmetry. The symmetry suppresses SUSY flavor
changing effects by making all squarks and sleptons degenerate in the symmetry
limit. Doublet-triplet splitting can arise simply, and non-trivial structure of
the quark and lepton masses emerges from the gauge symmetry, including the
"doubly lopsided" form.Comment: 11 pages, references adde
Predictive Models of Large Neutrino Mixing Angles
Several experimental results could be interpreted as evidence that certain
neutrino mixing angles are large, of order unity. However, in the context of
grand unified models the neutrino angles come out characteristically to be
small, like the KM angles. It is shown how to construct simple grand-unified
models in which neutrino angles are not only large but completely predicted
with some precision. Six models are presented for illustration.Comment: 19 pages, LaTe
Resonant leptogenesis in a predictive SO(10) grand unified model
An SO(10) grand unified model considered previously by the authors featuring
lopsided down quark and charged lepton mass matrices is successfully predictive
and requires that the lightest two right-handed Majorana neutrinons be nearly
degenerate in order to obtain the LMA solar neutrino solution. Here we use this
model to test its predictions for baryogenesis through resonant-enhanced
leptogenesis. With the conventional type I seesaw mechanism, the best
predictions for baryogenesis appear to fall a factor of three short of the
observed value. However, with a proposed type III seesaw mechanism leading to
three pairs of massive pseudo-Dirac neutrinos, resonant leptogenesis is
decoupled from the neutrino mass and mixing issues with successful baryogenesis
easily obtained.Comment: 22 pages including 1 figure; published version with reference adde
Lepton Flavor Violation in Supersymmetric SO(10) Grand Unified Models
The study for lepton flavor violation combined with the neutrino oscillation
may provide more information about the lepton flavor structure of the grand
unified theory. In this paper, we study two lepton flavor violation processes,
and , in the context of supersymmetric SO(10)
grand unified models. We find the two processes are both of phenomenological
interest. In particular the latter may be important in some supersymmetric
parameter space where the former is suppressed. Thus, Z-dacay may offer another
chance for looking for lepton flavor violation.Comment: 26 pages, 10 figure
SUSY GUTs under Siege : Proton Decay
SO(10) supersymmetric grand unified theories [SUSY GUTs] provide a beautiful
framework for physics beyond the standard model. Experimental measurements of
the three gauge couplings are consistent with unification at a scale GeV. In addition predictive models for fermion masses and
mixing angles have been found which fit the low energy data, including the
recent data for neutrino oscillations. SO(10) boundary conditions can be tested
via the spectrum of superparticles. The simplest models also predict neutron
and proton decay rates. In this paper we discuss nucleon decay rates and obtain
reasonable upper bounds. A clear picture of the allowed SUSY spectra as
constrained by nucleon decay is presented.Comment: 13 page
CP Violation in a Supersymmetric SO(10) x U(2)_{F} Model
A model based on SUSY SO(10) combined with U(2) family symmetry constructed
recently by the authors is generalized to include phases in the mass matrices
leading to CP violation. In contrast with the commonly used effective operator
approach, -dimensional Higgs fields are utilized to construct the
Yukawa sector. R-parity symmetry is thus preserved at low energies. The
symmetric mass textures arising from the left-right symmetry breaking chain of
SO(10) give rise to very good predictions for quark and lepton masses and
mixings. The prediction for agrees with the average of current
bounds from BaBar and Belle. In the neutrino sector, our predictions are in
good agreement with results from atmospheric neutrino experiments. Our model
favors both the LOW and QVO solutions to the solar neutrino anomaly; the matrix
element for neutrinoless double beta decay is highly suppressed. The leptonic
analog of the Jarlskog invariant, , is predicted to be of
.Comment: RevTeX4; 7 pages; typos corrected; clarification remarks added; more
references added. To appear in Physical Review
Bimaximal Neutrino Mixings from Lopsided Mass Matrices
Current solar and atmospheric neutrino oscillation data seem to favor a
bimaximal pattern for neutrino mixings where the matrix elements U_{e2} and
U_{\mu 3} are of order one, while U_{e3} is much smaller. We show that such a
pattern can be obtained quite easily in theories with ``lopsided'' mass
matrices for the charged leptons and the down type quarks. A relation
connecting the solar and atmospheric neutrino mixing angles is derived,
\tan^2\theta_{atm} \simeq 1+ \tan^2\theta_{sol}, which predicts \sin^2
2\theta_{atm} \simeq 0.97 corresponding to the best fit LMA solution for solar
neutrinos. Predictive schemes in SO(10) realizing these ideas are presented. A
new class of SO(10) models with lopsided mass matrices is found which makes use
of an adjoint VEV along the I_{3R} direction, rather than the traditional B-L
direction.Comment: 12 pages in LaTeX, no figure
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