809 research outputs found
A Positive Test for Fermi-Dirac Distributions of Quark-Partons
By describing a large class of deep inelastic processes with standard
parameterization for the different parton species, we check the characteristic
relationship dictated by Pauli principle: broader shapes for higher first
moments. Indeed, the ratios between the second and the first moment and the one
between the third and the second moment for the valence partons is an
increasing function of the first moment and agrees quantitatively with the
values found with Fermi-Dirac distributions.Comment: 15 pages LaTeX, 2 eps figures. Final version, to appear in Mod. Phys.
Lett.
Statistical Inspired Parton Distributions and the Violation of QPM Sum Rules
A quantum statistical parametrization of parton distributions has been
considered. In this framework, the exclusion Pauli principle connects the
violation of the Gottfried sum rule with the Ellis and Jaffe one, and implies a
defect in the Bjorken sum rule. However, in terms of standard parametrizations
of the polarized distributions a good description of the data is obtained once
a large gluon polarization is provided. Interestingly, in this description
there is no violation of the Bjorken sum rule.Comment: 10 pages, LateX + 15 figures, Talk given at ``Hadrons 96'' Workshop,
Novy Svet (CRIMEA), June 9-1
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
A search for Z' in muon neutrino associated charm production
In many extensions of the Standard Model the presence of an extra neutral
boson, Z', is invoked. A precision study of weak neutral-current exchange
processes involving only second generation fermions is still missing. We
propose a search for Z' in muon neutrino associated charm production. This
process only involves Z' couplings with fermions from the second generation. An
experimental method is thoroughly described using an ideal detector. As an
application, the accuracy reachable with present and future experiments has
been estimated.Comment: 13 pages, 3 figures, late
Semileptonic and Rare -meson transitions in a QCD relativistic potential model
Using a QCD relativistic potential model, previously applied to the
calculation of the heavy meson leptonic constants, we evaluate the form factors
governing the exclusive decays , and . In our approach the heavy meson is described as a
bound state, whose wave function is solution of the relativistic Salpeter
equation, with an instantaneous potential displaying Coulombic behaviour at
small distances and linear behaviour at large distances. The light vector meson
is described by using a vector current interpolating field, according to the
Vector Meson Dominance assumption. A Pauli-Villars regularized propagator is
assumed for the quarks not constituting the heavy meson. Our procedure allows
to avoid the description of the light meson in terms of wave function and
constituent quarks, and consequently the problem of boosting the light meson
wave function.
Assuming as an input the experimental results on , we
evaluate all the form factors describing the semileptonic and
rare transitions. The overall comparison with the data, whenever available, is
satisfactory.Comment: Latex, 19 pages, 3 figure
Low x Behaviour of the Isovector Nucleon Polarized Structure Function and the Bjorken Sum Rule
The combination g_1^p(x) - g_1^n(x) is derived from SLAC data on polarized
proton and deuteron targets, evaluated at Q^2 = 10 GeV^2, and compared with the
results of SMC experiment. The agreement is satisfactory except for the points
at the three lowest x, which have an important role in the SMC evaluation of
the l.h.s. of the Bjorken sum rule.Comment: 9 pages LaTeX + 4 eps figures, to appear in Modern Physics Letters
Phenomenological Bounds on B to Light Semileptonic Form Factors
The form factors for the weak currents between B and light mesons are studied
by relating them to the corresponding D form factors at q^2_{max} according to
HQET, by evaluating them at q^2=0 by QCD sum rules, and by assuming a polar q^2
dependence. The results found are consistent with the information obtained from
exclusive non-leptonic two-body decays and, with the only exception of A_1,
with lattice calculations.Comment: 8 LaTeX pages + 2 figures. Will appear in Mod. Phys. Lett.
Tackling dysfunction of mitochondrial bioenergetics in the brain
Oxidative phosphorylation (OxPhos) is the basic function of mitochondria, although the landscape of mitochondrial functions is continuously growing to include more aspects of cellular homeostasis. Thanks to the application of -omics technologies to the study of the OxPhos system, novel features emerge from the cataloging of novel proteins as mitochondrial thus adding details to the mitochondrial proteome and defining novel metabolic cellular interrelations, especially in the human brain. We focussed on the diversity of bioenergetics demand and different aspects of mitochondrial structure, functions, and dysfunction in the brain. Definition such as âmitoexomeâ, âmitoproteomeâ and âmitointeractomeâ have entered the field of âmitochondrial medicineâ. In this context, we reviewed several genetic defects that hamper the last step of aerobic metabolism, mostly involving the nervous tissue as one of the most prominent energy-dependent tissues and, as consequence, as a primary target of mitochondrial dysfunction. The dual genetic origin of the OxPhos complexes is one of the reasons for the complexity of the genotype-phenotype correlation when facing human diseases associated with mitochondrial defects. Such complexity clinically manifests with extremely heterogeneous symptoms, ranging from organ-specific to multisystemic dysfunction with different clinical courses. Finally, we briefly discuss the future directions of the multi-omics study of human brain disorders
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