278 research outputs found
A statistical approach for polarized parton distributions
A global next-to-leading order QCD analysis of unpolarized and polarized
deep-inelastic scattering data is performed with parton distributions
constructed in a statistical physical picture of the nucleon. The chiral
properties of QCD lead to strong relations between quarks and antiquarks
distributions and the importance of the Pauli exclusion principle is also
emphasized. We obtain a good description, in a broad range of and , of
all measured structure functions in terms of very few free parameters. We
stress the fact that at RHIC-BNL the ratio of the unpolarized cross sections
for the production of and in collisions, will directly probe
the behavior of the ratio for , a definite
and important test for the statistical model. Finally, we give specific
predictions for various helicity asymmetries for the production in
collisions at high energies, which will be measured with forthcoming
experiments at RHIC-BNL and are sensitive tests of the statistical model for
and .Comment: 49 pages, 27 eps figure
Neutrinoless double beta decay in SO(10) inspired seesaw models
By requiring the lower limit for the lightest right-handed neutrino mass,
obtained in the baryogenesis from leptogenesis scenario, and a Dirac neutrino
mass matrix similar to the up-quark mass matrix we predict small values for the
mass and for the matrix element responsible of the
neutrinoless double beta decay, around eV and
smaller than eV, respectively. The allowed range for the
mass of the heaviest right-handed neutrino is centered around the value of the
scale of B - L breaking in the SO(10) gauge theory with Pati-Salam intermediate
symmetry.Comment: 9 pages, RevTex4. Revised, title change
Intermediate Symmetries in the Spontaneous Breaking of Supersymmetric SO(10)
We study the supersymmetric spontaneous symmetry breaking of SO(10) into
SU(3)xSU(2)xU(1) for the most physically interesting cases of SU(5) or flipped
SU(5)xU(1) intermediate symmetries. The first case is more easily realized
while the second one requires a fine-tuning condition on the parameters of the
superpotential. This is because in the case of SU(5) symmetry there is at most
one singlet of the residual symmetry in each SO(10) irreducible representation.
We also point out on more general grounds in supersymmetric GUT's that some
intermediate symmetries can be exactly realized and others can only be
approximated by fine-tuning. In the first category, there could occur some
tunneling between the vacua with exact and approximate intermediate symmetry.
The flipped SU(5)xU(1) symmetry improves the unification of gauge couplings if
(B-L) is broken by (B-L)=1 scalars yielding right handed neutrino masses below
10^{14} GeV}.Comment: LaTex, 9 page
Further experimental tests for simple relations between unpolarized and polarized quark parton distributions
Some simple relations between unpolarized and polarized quark parton
distributions have direct experimental consequences which will be presented
here. In particular, we will see that it is possible to relate the deep
inelastic structure functions and , both for proton and deuteron, in
fair agreement with experimental data.Comment: 5 pages, in Latex, 3 figure
Polarized Quarks, Gluons and Sea in Nucleon Structure Functions
We perform a NLO analysis of polarized deep inelastic scattering data to test
two different solutions to the so called spin crisis: one of them based on the
axial gluon anomaly and consistent with the Bjorken sum rule and another one,
where the defects in the spin sum rules and in the Gottfried sum rule are
related. In this case a defect is also expected for the Bjorken sum rule. The
first solution is slightly favoured by the SLAC E154 results, but both options
seem to be consistent with the CERN SMC data.Comment: 19 pages, LateX, 6 figures. Figures included in the tex
Recent tests for the statistical parton distributions
We compare some recent experimental results obtained at DESY, SLAC and
Jefferson Lab., with the predictions of the statistical model, we have
previously proposed. The result of this comparison is very satisfactory.Comment: 12 pages, 6 eps figures, version to appear in Mod. Phys. Lett.
Magnetic field computation in a physically large domain with thin metallic shields
A three-dimensional edge element procedure is presented to analyze the magnetic field around thin shields embedded in a physically large domain. The shield region is eliminated from the computational domain and coupled boundary conditions named impedance network boundary conditions are imposed on the new boundary surfaces to take into account the field discontinuity produced by the eliminated shield. An experimental setup is built and the measured magnetic fields are compared to the results obtained by the proposed procedure
Supernova Neutrino Energy Spectra and the MSW Effect
The distortions in the thermal energy spectra for neutrinos produced in a
supernova when a resonant oscillation, MSW effect, occurs are determined. In
order to show this effect for some relevant and representative examples of
unified gauge models, we have chosen , and ,
with a particular scheme for fermion masses (DHR model). The
analysis has been performed for two choices of neutrinos parameters, predicted
by the above models, and capable to explain the solar neutrino problem. In both
cases one observes a strong distortion in the electron neutrino energy
spectrum. This effect, computed for a wide range of models has
produced the same results of the previous supersymmetric ones.Comment: 14 pages, plain LaTeX, 6 figures, revised version to be published in
Z. Phys.
Finite-Element Analysis of Temperature Increase in Vascularized Biological Tissues Exposed to RF Sources
A new model of numerical dosimetry is proposed for RF exposure. First, the specific absorption rate (SAR) is computed. Then, the heat transfer governed by the bio-heat equation with convection term is numerically solved by a finite-element method (FEM) procedure considering the discrete vascular model of the perfused tissue. By some manipulations of the FEM equations and by generating an adequate FEM mesh, it is possible to solve the thermal convection in the blood vessels considering a one-dimensional domain embedded in the fully three-dimensional domain where only the thermal diffusion is analyzed
- âŠ