170 research outputs found
The contributions of components to the axial charges of proton and its resonances
We calculate the axial charges of the proton and its resonances in the
framework of the constituent quark model, which is extended to include the
components. If 20% admixtures of the components in
the proton are assumed, the theoretical value for the axial charge in our model
is in good agreement with the empirical value, which can not be well reproduced
in the traditional constituent quark model even though the symmetry breaking or relativistic effect is taken into account. We also
predict an unity axial charge for with 30%
components constrained by the strong and electromagnetic decays.Comment: 4 pages, 4 table
Utilization of surveillance after polypectomy in the Medicare population
Background: Surveillance in patients with previous polypectomy was underused in the Medicare population in 1994. This study investigates whether expansion of Medicare reimbursement for colonoscopy screening in high-risk individuals has reduced the inappropriate use of surveillance.
Methods: We used Kaplan-Meier analysis to estimate time to surveillance and polyp recurrence rates for Medicare beneficiaries with a colonoscopy with polypectomy between 1998 and 2003 who were followed through 2008 for receipt of surveillance colonoscopy. Generalized Estimating Equations were used to estimate risk factors for: 1) failing to undergo surveillance and 2)
Stabilizing the Axion by Discrete Gauge Symmetries
The axion solution to the strong CP problem makes use of a global
Peccei-Quinn U(1) symmetry which is susceptible to violations from quantum
gravitational effects. We show how discrete gauge symmetries can protect the
axion from such violations. PQ symmetry emerges as an approximate global
symmetry from discrete gauge symmetries. Simple models based on Z_N symmetries
with N =11,12, etc are presented realizing the DFSZ axion and the KSVZ axion.
The discrete gauge anomalies are cancelled by a discrete version of the
Green-Schwarz mechanism. In the supersymmetric extension our models provide a
natural link between the SUSY breaking scale, the axion scale, and the
SUSY-preserving \mu term.Comment: 14 pages Late
Higgs sector and R-parity breaking couplings in models with broken U(1)_B-L gauge symmetry
Four different supersymmetric models based on SU(2)_L X U(1)_R X U(1)_B-L and
SU(2)_L X SU(2)_R X U(1)_B-L gauge symmetry groups are studied. U(1)_B-L
symmetry is broken spontaneously by a vacuum expectation value (VEV) of a
sneutrino field. The right-handed gauge bosons may obtain their mass solely by
sneutrino VEV. The physical charged lepton and neutrino are mixtures of
gauginos, higgsinos and lepton interaction eigenstates. Explicit formulae for
masses and mixings in the physical lepton fields are found. The spontaneous
symmetry breaking mechanism fixes the trilinear R-parity breaking couplings.
Only some special R-parity breaking trilinear couplings are allowed. There is a
potentially large trilinear lepton number breaking coupling - which is unique
to left-right models - that is proportional to the SU(2)_R gauge coupling g_R.
The couplings are parametrized by few mixing angles, making the spontaneous
R-parity breaking a natural ``unification framework'' for R-parity breaking
couplings in SUSYLR models.Comment: 19 pages, no figures, uses REVTeX. To be published in PR
Phenomenological Tests of Supersymmetric A_4 Family Symmetry Model of Neutrino Mass
Recently Babu, Ma and Valle proposed a model of quark and lepton mixing based
on symmetry. Within this model the lepton and slepton mixings are
intimately related. We perform a numerical study in order to derive the slepton
masses and mixings in agreement with present data from neutrino physics. We
show that, starting from three-fold degeneracy of the neutrino masses at a high
energy scale, a viable low energy neutrino mass matrix can indeed be obtained
in agreement with constraints on lepton flavour violating
and decays. The resulting slepton spectrum must necessarily
include at least one mass below 200 GeV which can be produced at the LHC. The
predictions for the absolute Majorana neutrino mass scale eV
ensure that the model will be tested by future cosmological tests and
searches.
Rates for lepton flavour violating processes
in the range of sensitivity of current
experiments are typical in the model, with BR(\mu \to e \gamma) \gsim
10^{-15} and the lower bound BR. To first
approximation, the model leads to maximal leptonic CP violation in neutrino
oscillations.Comment: 23 pages, 7 figure
Connecting bimaximal neutrino mixing to a light sterile neutrino
It is shown that if small neutrino masses owe their origin to the
conventional seesaw mechanism and the MNS mixing matrix is in the exact
bimaximal form, then there exist symmetries in the theory that allow one of the
righthanded neutrinos to become naturally massless, making it a candidate for
the sterile neutrino discussed in the literature. Departures from the exact
bimaximal limit leads to tiny mass for the sterile neutrino as well as its
mixing to the active neutrinos. This provides a minimal theoretical framework
where a simultaneous explanation of the solar, atmospheric and LSND
observations within the so-called 3+1 scenario may be possible.Comment: new references added; paper accepted for publication in Phys. Rev.
D.(rapid communications); note adde
Simple Model for (3+2) Neutrino Oscillations
We formulate a set of naturalness criteria for sterile neutrinos (\nu') to be
light, needed for reconciling the LSND neutrino anomaly with the other neutrino
data. A light sterile neutrino becomes as natural as the light active neutrinos
if it carries quantum numbers of a chiral gauge symmetry broken at the TeV
scale. The simplest such theory is shown to be an SU(2) gauge theory with the
\nu' transforming as a spin 3/2 multiplet. We develop this model and show that
it leads naturally to the phenomenologically viable (3+2) neutrino oscillation
scheme. We also present next-to-minimal models for light sterile neutrinos
based on a chiral U(1) gauge symmetry.Comment: 12 pages in LaTeX, typos corrected, reference adde
Natural R-Parity, \mu-term, and Fermion Mass Hierarchy From Discrete Gauge Symmetries
In the minimal supersymmetric Standard Model with seesaw neutrino masses we
show how R-parity can emerge naturally as a discrete gauge symmetry. The same
discrete symmetry explains the smallness of the \mu-term (the Higgsino mass
parameter) via the Giudice--Masiero mechanism. The discrete gauge anomalies are
cancelled by a discrete version of the Green--Schwarz mechanism. The simplest
symmetry group is found to be Z_4 with a charge assignment that is compatible
with grand unification. Several other Z_N gauge symmetries are found for
N=10,12,18,36 etc, with some models employing discrete anomaly cancellation at
higher Kac-Moody levels. Allowing for a flavor structure in Z_N, we show that
the same gauge symmetry can also explain the observed hierarchy in the fermion
masses and mixings.Comment: 22 pages, LaTe
Effective Mu-Term in Superstring Theory
In four-dimensional compactifications of the heterotic superstring theory the
K\"ahler potential has a form which generically induces a superpotential mass
term for Higgs particles once supersymmetry is broken at low energies. This
``-term'' is analyzed in a model-independent way at the tree level and in
the one-loop approximation, and explicit expressions are obtained for orbifold
compactifications. Additional contributions which arise in the case of
supersymmetry breaking induced by gaugino condensation are also discussed.Comment: 28 pages (LaTeX, 2 figures attached as uuencoded ps files), NUB-3084
- IC/94/72 - CPTH-A282.0194, to appear in Nuclear Physics B (revised version
contains modifications due to the presence of extra massless states at some
special points of the moduli space in orbifold models
- …