2,427 research outputs found
Pion Form Factor in Chiral Limit of Hard-Wall AdS/QCD Model
We develop a formalism to calculate form factor and charge density
distribution of pion in the chiral limit using the holographic dual model of
QCD with hard-wall cutoff. We introduce two conjugate pion wave functions and
present analytic expressions for these functions and for the pion form factor.
They allow to relate such observables as the pion decay constant and the pion
charge electric radius to the values of chiral condensate and hard-wall cutoff
scale. The evolution of the pion form factor to large values of the momentum
transfer is discussed, and results are compared to existing experimental data.Comment: 21 page, 7 figures. Short comparison with NJL predictions for pion
radius and new references added. To be published in Phys.Rev.
Bjorken Sum Rule and pQCD frontier on the move
The reasonableness of the use of perturbative QCD notions in the region close
to the scale of hadronization, i.e., below \lesssim 1 \GeV is under study.
First, the interplay between higher orders of pQCD expansion and higher twist
contributions in the analysis of recent Jefferson Lab (JLab) data on the
Generalized Bjorken Sum Rule function at is studied. It is shown that the inclusion of the higher-order
pQCD corrections could be absorbed, with good numerical accuracy, by change of
the normalization of the higher-twist terms. Second, to avoid the issue of
unphysical singularity (Landau pole at Q=\Lambda\sim 400 \MeV ), we deal with
the ghost-free Analytic Perturbation Theory (APT) that recently proved to be an
intriguing candidate for a quantitative description of light quarkonia spectra
within the Bethe-Salpeter approach. The values of the twist coefficients
extracted from the mentioned data by using the APT approach provide
a better convergence of the higher-twist series than with the common pQCD. As
the main result, a good quantitative description of the JLab data down to
350 MeV is achieved.Comment: 10 pages, 3 figures, minor change
Helicity-dependent photoabsorption cross sections on the nucleon
We examine the energy dependence of single-meson photoproduction as it
contributes to the Gerasimov-Drell-Hearn (GDH) sum rule. For photon energies
above approximately 1 GeV, through the full resonance region, this contribution
dominates the proton sum rule integral. Over the same energy region, our
single-pion contribution to the neutron sum rule also qualitatively follows a
recent set of GDH data. The predicted neutral-pion contribution to the neutron
sum rule is nearly zero above 1 GeV in this result. The SAID and Mainz (MAID)
results are very different for a number of observables over this energy region.Comment: 7 pages, 5 figur
Reciprocal space study of Heisenberg exchange interactions in ferromagnetic metals
The modern quantum theory of magnetism in solids is getting commonly derived
using Green's functions formalism. The popularity draws itself from remarkable
opportunities to capture the microscopic landscape of exchange interactions,
starting from a tight-binding representation of the electronic structure.
Indeed, the conventional method of infinitesimal spin rotations, considered in
terms of local force theorem, opens vast prospects of investigations regarding
the magnetic environment, as well as pairwise atomic couplings. However, this
theoretical concept practically does not devoid of intrinsic inconsistencies.
In particular, naturally expected correspondence between single and pairwise
infinitesimal spin rotations is being numerically revealed to diverge. In this
work, we elaborate this question on the model example and canonical case of bcc
iron. Our analytical derivations discovered the principal preference of on-site
magnetic precursors if the compositions of individual atomic interactions are
in focus. The problem of extremely slow or even absent spatial convergence
while considering metallic compounds was solved by suggesting the original
technique, based on reciprocal space framework. Using fundamental Fourier
transform-inspired interconnection between suggested technique and traditional
spatial representation, we shed light on symmetry breaking in bcc Fe on the
level of orbitally decomposed total exchange surrounding
Політичне лідерство як феномен сучасного суспільства
Герасимович В. А. Політичне лідерство як феномен сучасного суспільства / В. А. Герасимович // Людина, суспільство, політика: актуальні виклики сучасності: матеріали ІІ Міжнародної науково-практичної конференції (м. Одеса, 13-14 лютого 2015 р.) / НУ «ОЮА», Одеське відділення Міжнародної асоціації студентів політологічної науки, за заг. ред. Д. В. Яковлева – Одеса : НУ «ОЮА», 2015. – С. 90-92
- …