175 research outputs found
Coulomb dissociation of a fast pion into two jets
We calculate the electromagnetic contribution to the scattering amplitude of
pion diffractive dissociation into di-jets which is described by one photon
exchange. The result shows that the factorization procedure known for the
description of exclusive reactions holds also for this quasi-exclusive process.
We find that the longitudinal momentum distribution of di-jets does not depend
on the form of the pion distribution amplitude. We discuss the magnitude of the
cross section.Comment: 7 pages, 3 .eps figures, Late
Two−photon Processes in Organometallic Molecules and Clusters: T−T Absorption of Group IV Metal Complexes
Triplet – triplet absorption of d0 metal complexes was for the first time revealed and studied by means of pulse photolysis and electron-exchange (Dexter) resonant energy transfer energy transfer.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3539
The B-Meson Distribution Amplitude in QCD
The B-meson distribution amplitude is calculated using QCD sum rules. In
particular we obtain an estimate for the integral relevant to exclusive
B-decays \lambda_B = 460 \pm 110 MeV at the scale 1 GeV. A simple QCD-motivated
parametrization of the distribution amplitude is suggested.Comment: 17 pages, 8 figures, Latex styl
Carbonitration of a tool for pressing stainless steel pipes
To upgrade the operational stability of the tool at LLC “Karbaz”, Sumy, Ukraine, carbonation of tools and samples for research in melts of salts of cyanates and carbonates of alkali metals at 570–580 °C was carried out to obtain a layer thickness of 0.15–0.25 mm and a hardness of 1000–1150 НV. Tests of the tool in real operating conditions were carried out at the press station at LLC “VO Oscar”, Dnipro, Ukraine. The purpose of the test is to evaluate the feasibility of carbonitriding of thermo-strengthened matrix rings and needle-mandrels to improve their stability, hardness, heat resistance, and endurance. If the stability of matrix rings after conventional heat setting varies around 4–6 presses, the rings additionally subjected to chemical-thermal treatment (carbonitration) demonstrated the stability of 7–9 presses due to higher hardness, heat resistance, the formation of a special structure on the surface due to carbonitration in salt melts cyanates and carbonates. Nitrogen and carbon present in the carbonitrided layer slowed down the processes of transformation of solid solutions and coagulation of carbonitride phases. The high hardness of the carbonitrified layer is maintained up to temperatures above 650 °C. If the stability of the needle-mandrels after conventional heat treatment varies between 50–80 presses, the needles, additionally subjected to chemical-thermal treatment (carbonitration) showed the stability of 100–130 presses due to higher hardness, wear resistance, heat resistance, the formation of a special surface structure due to carbonitration in melts of salts of cyanates and carbonates
Analysis of the vertexes , and radiative decays ,
In this article, we study the vertexes and with the light-cone QCD sum rules, then assume the vector meson
dominance of the intermediate , and , and
calculate the radiative decays and .Comment: 28 pages, 4 tables, revised versio
Low Temperature Static and Dynamic Behavior of the Two-Dimensional Easy-Axis Heisenberg Model
We apply the self-consistent harmonic approximation (SCHA) to study static
and dynamic properties of the two-dimensional classical Heisenberg model with
easy-axis anisotropy. The static properties obtained are magnetization and spin
wave energy as functions of temperature, and the critical temperature as a
function of the easy-axis anisotropy. We also calculate the dynamic correlation
functions using the SCHA renormalized spin wave energy. Our analytical results,
for both static properties and dynamic correlation functions, are compared to
numerical simulation data combining cluster-Monte Carlo algorithms and Spin
Dynamics. The comparison allows us to conclude that far below the transition
temperature, where the SCHA is valid, spin waves are responsible for all
relevant features observed in the numerical simulation data; topological
excitations do not seem to contribute appreciably. For temperatures closer to
the transition temperature, there are differences between the dynamic
correlation functions from SCHA theory and Spin Dynamics; these may be due to
the presence of domain walls and solitons.Comment: 12 pages, 14 figure
Dynamical spin correlations in Heisenberg ladder under magnetic field and correlation functions in SO(5) ladder
The zero-temperature dynamical spin-spin correlation functions are calculated
for the spin-1/2 two-leg Heisenberg ladder in a magnetic field above the lower
critical field Hc1. The dynamical structure factors are calculated which
exhibit both massless and massive excitations. These modes appear in different
sectors characterized by the parity in the rung direction and by the momentum
in the direction of the chains. The structure factors have power-law
singularities at the lower edges of their support. The results are also
applicable to spin-1 Heisenberg chain. The implications are briefly discussed
for various correlation functions and the pi-resonance in the SO(5) symmetric
ladder model.Comment: 15 pages, 6 figures, added references; final version to appear in
Phys. Rev.
The longitudinal cross section of vector meson electroproduction
We analyze electroproduction of light vector mesons (V=rho, phi and omega) at
small Bjorken-x in the handbag approach in which the process factorizes into
general parton distributions and partonic subprocesses. The latter are
calculated in the modified perturbative approach where the transverse momenta
of the quark and antiquark forming the vector meson are retained and Sudakov
suppressions are taken into account. Modeling the generalized parton
distributions through double distributions and using simple Gaussian
wavefunctions for the vector mesons, we compute the longitudinal cross sections
at large photon virtualities. The results are in fair agreement with the
findings of recent experiments performed at HERA and HERMES.Comment: 27 pages, 20 figures, using LATEX with graphic
The transition form factors for semi-leptonic weak decays of in QCD sum rules
Within the Standard Model, we investigate the semi-leptonic weak decays of
. The various form factors of transiting to a single charmed
meson () are studied in the framework of the QCD sum rules.
These form factors fully determine the rates of the weak semi-leptonic decays
of and provide valuable information about the non-perturbative QCD
effects. Our results indicate that the decay rate of the semi-leptonic weak
decay mode is at order of .Comment: 28 pages, 6 figures, revised version to be published in Eur.Phys.J.
Applicability of perturbative QCD to decays
We develop perturbative QCD factorization theorem for the semileptonic heavy
baryon decay , whose form factors are
expressed as the convolutions of hard quark decay amplitudes with universal
and baryon wave functions. Large logarithmic
corrections are organized to all orders by the Sudakov resummation, which
renders perturbative expansions more reliable. It is observed that perturbative
QCD is applicable to decays for velocity transfer
greater than 1.2. Under requirement of heavy quark symmetry, we predict the
branching ratio , and determine
the and baryon wave functions.Comment: 12 pages in Latex file, 3 figures in postscript files, some results
are changed, but the conclusion is the sam
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