6,867 research outputs found
Seesaw Neutrino Mass and New U(1) Gauge Symmetry
The three electroweak doublet neutrinos of the Standard
Model may acquire small seesaw masses, using either three Majorana fermion
singlets or three Majorana fermion triplets .
It is well-known that the former accommodates the U(1) gauge symmetry . It
has also been shown some years ago that the latter supports a new
gauge symmetry. Here we study two variations of this , one for two
and one , the other for one and two . Phenomenological
consequences are discussed.Comment: 16 pages, 3 figures, LaTex, 2 eps files,text adde
Universal Seesaw from Left-Right and Peccei-Quinn Symmetry Breaking
To generate the lepton and quark masses in the left-right symmetric models,
we can consider a universal seesaw scenario by integrating out heavy fermion
singlets which have the Yukawa couplings with the fermion and Higgs doublets.
The universal seesaw scenario can also accommodate the leptogenesis with
Majorana or Dirac neutrinos. We show the fermion singlets can obtain their
heavy masses from certain global symmetry breaking, which is driven by one
complex scalar singlet or two. The global symmetry can be identified to the
Peccei-Quinn symmetry since it is mediated to the standard model quarks at tree
and/or loop level.Comment: 4 page
A non-standard CP transformation leading to maximal atmospheric neutrino mixing
We discuss a neutrino mass matrix originally found by Babu,
Ma, and Valle (BMV) and show that this mass matrix can be characterized by a
simple algebraic relation. From this relation it follows that atmospheric
neutrino mixing is exactly maximal while at the same time an arbitrary mixing
angle of the lepton mixing matrix is allowed and--in the
usual phase convention--CP violation in mixing is maximal; moreover, neither
the neutrino mass spectrum nor the solar mixing angle are restricted. We put
forward a simple seesaw extension of the Standard Model where the family lepton
numbers are softly broken by the Majorana mass terms of the right-handed
neutrino singlets and the BMV mass matrix results from a non-standard
symmetry.Comment: 13 pages, plain LaTeX, no figures; minor modifications, final version
for Phys. Lett.
A discrete symmetry group for maximal atmospheric neutrino mixing
We propose a discrete non-abelian symmetry group which enforces maximal
atmospheric neutrino mixing, while and the solar mixing angle
remains undetermined; without finetuning, will be
large but non-maximal. Our extension of the Standard Model has three
right-handed neutrino singlets and implements the seesaw mechanism.
Furthermore, we have an enlarged scalar sector with three Higgs doublets and
two scalar gauge singlets; the latter have masses and vacuum expectation values
of the order of the seesaw scale. Lepton mixing stems exclusively from the
Majorana mass matrix, where non-diagonal elements are generated by the
vacuum expectation values of the scalar singlets. The model predicts a neutrino
mass spectrum with and the effective Majorana mass of
neutrinoless decay is equal to .Comment: 9 pages, no figures, plain LaTeX; new section added and misprints
corrected, version to be published in Phys. Lett.
Absolutely stable proton and lowering the gauge unification scale
A unified model is constructed, based on flipped SU(5) in which the proton is absolutely stable. The model requires the existence of new leptons with masses of order the weak scale. The possibility that the unification scale could be extremely low is discussed
Radiative Seesaw in SO(10) with Dark Matter
High energy accelerators may probe into dark matter and the seesaw neutrino
mass scales if they are not much heavier than ~O(TeV). In the absence of
supersymmetry, we extend a class of SO(10) models to predict well known cold
dark matter candidates while achieving precision unification with
experimentally testable proton lifetime. The most important prediction is a new
radiative seesaw formula of Ma type accessible to accelerator tests while the
essential small value of its quartic coupling also emerges naturally. This
dominates over the high-scale seesaw contributions making a major impact on
neutrino physics and dark matter, opening up high prospects as a theory of
fermion masses.Comment: 11 pages LaTex, no figures.hep-ph, astro-ph, hep-th; Version accepted
in Phys. Lett.
Inverse Hierarchy Approach to Fermion Masses
The first fermion family might play a special role in understanding the
physics of flavour. This possibility is suggested by the observation that the
up-down splitting within quark families increases with the family number: , , . We construct a model that realizes this
feature of the spectrum in a natural way. The inter-family hierarchy is first
generated by radiative phenomena in a sector of heavy isosinglet fermions and
then transferred to quarks by means of a universal seesaw. A crucial role is
played by left-right parity and up-down isotopic symmetry. No family symmetry
is introduced. The model implies 0.5 and the Cabibbo angle is forced
to be . The top quark is naturally in the 100 GeV range,
but not too heavy: 150 GeV. Inspired by the mass matrices obtained in
the model for quarks, we suggest an ansatz also including charged leptons. The
differences between -, - and -type fermions are simply parametrized by
three complex coefficients \eps{u}, \eps{d} and \eps{e}. Additional
consistent predictions are obtained: =100-150 MeV and 0.75.Comment: 19 pages (standard TeX) + 1 table (cut out and LaTeX separately) + 1
figure (cut out and postscript separately); 2 additional figures available by
fax upon request, LBL-32889, LMU-13/9
CP Test in J/Psi -> gamma phi phi Decay
We propose to test CP symmetry in the decay \jp\to \gamma \phi\phi, for
which large data sample exists at BESII, and a data sample of
's will be collected with BESIII and CLEO-C program. We suggest some CP
asymmetries in this decay mode for CP test. Assuming that CP violation is
introduced by the electric- and chromo-dipole moment of charm quark, these CP
asymmetries can be predicted by using valence quark models. Our work shows a
possible way to get information about the electric- and chromo-dipole moment of
charm quark, which is little known. Our results show that with the current data
sample of , electric- and chromo-dipole moment can be probed at order
of . In the near future with a data sample, these
moments can be probed at order of .Comment: Misprints corrected. To appear in Phys. Lett.
An SO(10) GUT With See-Saw Masses For All Fermions
We propose an SO(10) grand unified theory which has the simplest Higgs
structure discussed so far in the literature. We include only two Higgs
scalars, a 210-plet and a 16-plet. In addition to the regular fermions we
include one singlet, whose mass term breaks chiral symmetry, so that fermions
can get masses. All fermions acquire see-saw masses, since there are no Higgs
bi-doublets. Required neutrino masses with large mixing as well as leptogenesis
are possible in this model.Comment: 16 pages, 3 figure
Embedding A4 into left-right flavor symmetry: Tribimaximal neutrino mixing and fermion hierarchy
We address two fundamental aspects of flavor physics: the mass hierarchy and
the large lepton mixing angles. On one side, left-right flavor symmetry
realizes the democratic mass matrix patterns and explains why one family is
much heavier than the others. On the other side, discrete flavor symmetry such
as A4 leads to the observed tribimaximal mixing for the leptons. We show that,
by explicitly breaking the left-right flavor symmetry into the diagonal A4, it
is possible to explain both the observed charged fermion mass hierarchies and
quark and lepton mixing angles. In particular we predict a heavy 3rd family,
the tribimaximal mixing for the leptons, and we suggest a possible origin of
the Cabibbo and other mixing angles for the quarks.Comment: 9 pages, uses revtex4 and axodraw.st
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