8,664 research outputs found
Fragmentation Function and Nucleon Transversity Distribution in a Diquark Model
Based on a simple quark-diquark model, we propose a set of unpolarized,
longitudinally polarized and transversely polarized fragmentation functions for
the by fitting the unpolarized production data in annihilation. It is found that the helicity structure of the obtained
fragmentation functions is supported by the all available
experimental data on the longitudinal polarization. Within the same
framework of the diquark model, the nucleon transversity distributions are
presented and consistent descriptions of the available HERMES data on the
azimuthal spin asymmetries in pion electroproduction are obtained. Furthermore,
the spin transfers to the transversely polarized in the charged
lepton DIS on a transversely polarized nucleon target are predicted for future
experiments.Comment: Talk given in a seminar of U. Santa Mari
SU(5) Completion of the Dark Scalar Doublet Model of Radiative Neutrino Mass
Adding a second scalar doublet (eta^+,eta^0) and three neutral singlet
fermions N_{1,2,3} to the Standard Model of particle interactions with a new
Z_2 symmetry, it has been shown that eta^0_R or eta^0_I is a good dark-matter
candidate and seesaw neutrino masses are generated radiatively. A minimal
extension of this new idea is proposed to allow for its SU(5) completion.
Supersymmetric unification is then possible, and leptoquarks of a special kind
are predicted at the TeV scale.Comment: 6 pages, 2 figures, 1 tabl
Triplicity of Quarks and Leptons
Quarks come in three colors and have electric charges in multiples of
one-third. There are also three families of quarks and leptons. Whereas the
first two properties can be understood in terms of unification symmetries such
as SU(5), SO(10), or E_6, why there should only be three families remains a
mystery. I propose how all three properties involving the number three are
connected in a fivefold application of the gauge symmetry SU(3).Comment: 10 pages, including 2 figure
Efficacious Additions to the Standard Model
If split supersymmetry can be advocated as a means to have gauge-coupling
unification as well as dark matter, another plausible scenario is to enlarge
judiciously the particle content of the Standard Model to achieve the same
goals without supersymmetry. A simple efficacious example is presented.Comment: 6 pages, no figure, one reference added, version to appear in PL
Sivers function in light-cone quark model and azimuthal spin asymmetries in pion electroproduction
We perform a calculation of Sivers function in a light-cone SU(6)
quark-diquark model with both scalar diquark and vector diquark spectators. We
derive the transverse momentum dependent light-cone wave function of the proton
by taking into account the Melosh-Wigner rotation. By adopting one-gluon
exchange, we obtain a non-vanishing Sivers function of quark from
interference of proton spin amplitudes. We analyze the
weighted Sivers asymmetries in , and electroproduction
off transverse polarized proton target, averaged and not averaged by the
kinematics of HERMES experiment.Comment: 17 LaTex pages, 2 figures. Final version for journal publicatio
Towards a Casimir force measurement between micromachined parallel plate structures
Ever since its prediction, experimental investigation of the Casimir force has been of great scientific interest. Many research groups have successfully attempted quantifying the force with different device geometries; however, measurement of the Casimir force between parallel plates with sub-micron separation distance is still a challenging task, since it becomes extremely difficult to maintain sufficient parallelism between the plates. The Casimir force can significantly influence the operation of micro devices and to realize reliable and reproducible devices it is necessary to understand and experimentally verify the influence of the Casimir force at sub-micron scale. In this paper, we present the design principle, fabrication and characterization of micromachined parallel plate structures that could allow the measurement of the Casimir force with tunable separation distance in the range of 100 to 1000 nm. Initially, a gold coated parallel plate structure is explored to measure the Casimir force, but also other material combinations could be investigated. Using gold-silicon eutectic bonding, a reliable approach to bond chips with integrated suspended plates together with a well-defined separation distance in the order of 1â2 ÎŒm is developed
Momentum sum rules for fragmentation functions
Momentum sum rules for fragmentation functions are considered. In particular,
we give a general proof of the Sch\"afer-Teryaev sum rule for the transverse
momentum dependent Collins function. We also argue that corresponding sum rules
for related fragmentation functions do not exist. Our model-independent
analysis is supplemented by calculations in a simple field-theoretical model.Comment: 12 pages; v2: Eqs. (44,46) added, minor additional changes, to appear
in Phys. Lett.
Sivers vs. Collins effect in azimuthal single spin asymmetries in pion production in SIDIS
Recently it has been argued that the transverse momentum dependent twist-2
Sivers distribution function does not vanish in QCD. Therefore both, the
Collins and Sivers effects, should be considered in order to explain the
azimuthal single spin asymmetries A(UL) in pion production in semi-inclusive
deeply inelastic lepton scattering of a longitudinally polarized target. On the
basis of presently available phenomenological information on the Sivers
function we estimate that for those asymmetries A(UL) in the kinematic region
of the HERMES experiments the Sivers effect can be neglected with respect to
the Collins effect. It is argued that the same feature holds also for the
COMPASS and CLAS experiments. This justifies theoretical approaches to
understand the HERMES data on the basis of the Collins effect only.Comment: 8 pages, 4 figures. References added, small changes in text, Appendix
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Azimuthal single spin asymmetries in SIDIS in the light of chiral symmetry breaking
An attempt is made to understand the z-dependence of the azimuthal single
spin asymmetries observed by the HERMES collaboration in terms of chiral models
based on effective quark and Goldstone boson degrees of freedom. The effects of
respectively neglecting and considering Gaussian intrinsic parton transverse
momenta and the Sivers effect are explored. Predictions for the transverse
target polarization experiment at HERMES are presented.Comment: 14 pages, 18 figure
Demonstration project on epilepsy in Brazil - Outcome assessment
Purpose: To assess the outcome of patients with epilepsy treated at primary care health units under the framework of the demonstration project on epilepsy in Brazil, part of the WHO/ILAE/IBE Global Campaign Against Epilepsy. Method. We assessed the outcome of patients treated at four primary health units. The staff of the health units underwent information training in epilepsy. The outcome assessment was based on: 1) reduction of seizure frequency, 2) subjective perception from the patient's and the physician's point of view, 3) reduction of absenteeism, 4) social integration (school and work), and 5) sense of independence. Results: A total of 181 patients (93 women - 51%) with a mean age of 38 (range from 2 to 86) years were studied. The mean follow-up was 26 months (range from 1 to 38 months, 11 patients had follow-up of less than 12 months). Seizure frequency was assessed based on a score system, ranging from 0 (no seizure in the previous 24 months) to 7 (> 10 seizure/day). The baseline median seizure-frequency score was 3 (one to three seizures per month). At the end of the study the median seizure-frequency score was 1 (one to three seizures per year). The patients' and relatives' opinions were that in the majority (59%) the health status had improved a lot, some (19%) had improved a little, 20% experienced no change and in 2% the health status was worse. With regard to absenteeism, social integration and sense of independence, there were some modest improvements only. Discussion: The development of a model of epilepsy treatment at primary health level based on the existing health system, with strategic measures centred on the health care providers and the community, has proved to be effective providing important reductions in seizure frequency, as well as in general well being. This model can be applied nationwide, as the key elements already exist provided that strategic measures are put forward in accordance with local health providers and managers
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