306 research outputs found
Contact interactions in low scale string models with intersecting -branes
We evaluate the tree level four fermion string amplitudes in the TeV string
mass scale models with intersecting -branes. The coefficient functions of
contact interactions subsuming the contributions of string Regge resonance and
winding mode excitations are obtained by subtracting out the contributions from
the string massless and massive momentum modes. Numerical applications are
developed for the Standard Model like solution of Cremades, Ibanez, and
Marchesano for a toroidal orientifold with four intersecting -brane stacks.
The chirality conserving contact interactions of the quarks and leptons are
considered in applications to high energy collider and flavor changing neutral
current phenomenology. The two main free parameters consist of the string and
compactification mass scales, and . Useful constraints on these
parameters are derived from predictions for the Bhabha scattering differential
cross section and for the observables associated to the mass shifts of the
neutral meson systems and the lepton number
violating three-body leptonic decays of the charged leptons and .Comment: 34 pages, 7 figure
Quenching of the Deuteron in Flight
We investigate the Lorentz contraction of a deuteron in flight. Our starting
point is the Blankenbecler-Sugar projection of the Bethe-Salpeter equation to a
3-dimensional quasi potential equation, wqhich we apply for the deuteron bound
in an harmonic oscillator potential (for an analytical result) and by the Bonn
NN potential for a more realistic estimate. We find substantial quenching with
increasing external momenta and a significant modification of the high momentum
spectrum of the deuteron.Comment: 11 pages, 4 figure
Photoproduction and Radiative Decay of Spin 1/2 and 3/2 Pentaquarks
We study photoproduction and radiative decays of pentauqarks paying
particular attention to the differences between spin-1/2 and spin-3/2, positive
and negative parities of pentaquarks. Detailed study of these processes can not
only give crucial information about the spin, but also the parity of
pentaquarks.Comment: 14 pages, 7 figure
Study of a Neutrino Mass Texture Generated in Supergravity with Bilinear R-Parity Violation
We study a particular texture of the neutrino mass matrix generated in
supergravity with bilinear R-Parity violation. The relatively high value of
makes the one-loop contribution to the neutrino mass matrix as
important as the tree-level one. The atmospheric angle is nearly maximal, and
its deviation from maximal mixing is related to the smallness of the ratio
between the solar and atmospheric mass scales. There is also a common origin
for the small values of the solar and reactor angles, but the later is much
smaller due the large mass ratio between the lightest two neutrinos. There is a
high dependence of the neutrino mass differences on the scalar mass and
the gaugino mass , but a smaller one of the mixing angles on the same
sugra parameters. Measurements of branching ratios for the neutralino decays
can give important information on the parameters of the model. There are good
prospects at a future Linear Collider for these measurements, but a more
detailed analysis is necessary for the LHC.Comment: 21 pages, 9 figure
Microscopic calculation of 6Li elastic and transition form factors
Variational Monte Carlo wave functions, obtained from a realistic Hamiltonian
consisting of the Argonne v18 two-nucleon and Urbana-IX three-nucleon
interactions, are used to calculate the 6Li ground-state longitudinal and
transverse form factors as well as transition form factors to the first four
excited states. The charge and current operators include one- and two-body
components, leading terms of which are constructed consistently with the
two-nucleon interaction. The calculated form factors and radiative widths are
in good agreement with available experimental data.Comment: 9 pages, 2 figures, REVTeX, submitted to Physical Review Letters,
with updated introduction and reference
Cone Genesis Tracing by the Chrnb4-EGFP Mouse Line: Evidences of Cellular Material Fusion after Cone Precursor Transplantation.
The cone function is essential to mediate high visual acuity, color vision, and daylight vision. Inherited cone dystrophies and age-related macular degeneration affect a substantial percentage of the world population. To identify and isolate the most competent cells for transplantation and integration into the retina, cone tracing during development would be an important added value. To that aim, the Chrnb4-EGFP mouse line was characterized throughout retinogenesis. It revealed a sub-population of early retinal progenitors expressing the reporter gene that is progressively restricted to mature cones during retina development. The presence of the native CHRNB4 protein was confirmed in EGFP-positive cells, and it presents a similar pattern in the human retina. Sub-retinal transplantations of distinct subpopulations of Chrnb4-EGFP-expressing cells revealed the embryonic day 15.5 high-EGFP population the most efficient cells to interact with host retinas to provoke the appearance of EGFP-positive cones in the photoreceptor layer. Importantly, transplantations into the DsRed retinas revealed material exchanges between donor and host retinas, as >80% of transplanted EGFP-positive cones also were DsRed positive. Whether this cell material fusion is of significant therapeutic advantage requires further thorough investigations. The Chrnb4-EGFP mouse line definitely opens new research perspectives in cone genesis and retina repair
Report of the GDR working group on the R-parity violation
This report summarizes the work of the "R-parity violation group" of the
French Research Network (GDR) in Supersymmetry, concerning the physics of
supersymmetric models without conservation of R-parity at HERA, LEP, Tevatron
and LHC and limits on R-parity violating couplings from various processes. The
report includes a discussion of the recent searches at the HERA experiment,
prospects for new experiments, a review of the existing limits, and also
theoretically motivated alternatives to R-parity and a brief discussion on the
implications of R-parity violation on the neutrino masses.Comment: 60 pages, LaTeX, 22 figures, 2 table
The Gluon Exchange Interaction Between Constituent Quarks
The interaction mediated by irreducible pion and gluon exchange between
constituent quarks is calculated and shown to have a strong tensor component,
which tends to cancel the pion exchange tensor interaction between quarks. Its
spin-spin component is somewhat weaker than the pion exchange spin-spin
interaction, while its central and spin-orbit components are small in
comparison to the corresponding single gluon exchange interactions. The
combination of the gluon exchange interaction with the single pion
exchange interaction and a weak gluon exchange interaction between constituent
quarks has the qualitative features required for understanding the hyperfine
splittings of the spectra of the nucleon and the resonances.Comment: LaTeX, 17 pages, 5 Postscript figure
Peripheral N Scattering: A Tool For Identifying The Two Pion Exchange Component Of The NN Potential
We study elastic N scattering and produce a quantitative correlation
between the range of the effective potential and the energy of the system. This
allows the identification of the waves and energies for which the scattering
may be said to be peripheral. We then show that the corresponding phase shifts
are sensitive to the tail of the NN potential, which is due to the exchange of
two pions. However, the present uncertainties in the experimental phase shifts
prevent the use of N scattering to discriminate the existing models
for the NN interaction.Comment: 19 pages, 6 PostScript figures, RevTeX, to be appear in Phys. Rev.
Radiative Neutron-Proton Capture in Effective Chiral Lagrangians
We calculate the cross-section for the thermal
process in chiral perturbation theory to next-to-next-to-leading order using
heavy-fermion formalism. The exchange current correction is found to be
in amplitude and the chiral perturbation at one-loop order
gives the cross section \sigma_{th}^{np}=(334\pm 2)\ {\mbox mb} which is in
agreement with the experimental value (334.2\pm 0.5)\ {\mbox mb}. Together
with the axial charge transitions, this provides a strong support for the power
of chiral Lagrangians for nuclear physics.Comment: 9 pages, revtex, uses epsfig.sty, 2 uuencoded figure
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