119 research outputs found
On U(1)-charged domain walls
A classical field system of two interacting fields -- a real Higgs field and
a complex scalar field -- is considered. It is shown that in such field system
a non-trivial solution exists, which is U(1) charged topological kink. Some
questions of stability of the obtained solution are discussed. An improved
variational procedure for searching of topological U(1) charged solutions is
given.Comment: 16 pages, LaTeX, 4 PostScript figure
Higher order forward spin polarizability
As a guideline for future experiments to extract the four (leading) spin
polarizabilities of the nucleon, we have constructed the forward amplitude for
polarized Compton scattering by dispersion integrals. These integrals have been
saturated by recently measured helicity-dependent photoabsorption cross
sections as well as predictions for pion photoproduction multipoles from
several phenomenological descriptions and chiral perturbation theory. The
comparison of these results corroborates the strategy to extract the spin
polarizabilities by fitting them to polarized Compton data and fixing all
higher order spin effects by dispersion relations based on pion photoproduction
multipoles.Comment: 21 pages, 6 figures, 3 Tables; version to appear in Phys. Lett.
Perturbative approach to the hydrogen atom in strong magnetic field
The states of hydrogen atom with principal quantum number n <= 3 and zero
magnetic quantum number in constant homogeneous magnetic field H are
considered. The perturbation theory series is summed with the help of Borel
transformation and conformal mapping of the Borel variable. Convergence of
approximate energy eigenvalues and their agreement with corresponding existing
results are observed for external fields up to n^3 H ~ 5. The possibility of
restoring the asymptotic behaviour of energy levels using perturbation theory
coefficients is also discussed.Comment: LaTeX, 8 pages with 5 eps figure
ЭФФЕКТИВНОСТЬ ПРИМЕНЕНИЯ МАЛОЙ АВИАЦИИ ДЛЯ ХИМИЧЕСКИХ ОБРАБОТОК В УСЛОВИЯХ РЕСПУБЛИКИ БЕЛАРУСЬ
One of the key elements of a successful use of modern intensive technologies of crop cultivation is a timely and high quality chemical treatment of young crops. The paper considers the possibility of the use of small aircraft means for chemical treatment, describes the advantages and disadvantages of this method. The parameters of the effective use of specialized planes “Fermer-3” have been substantiated, and their economic evaluation has been carried out.Одним из ключевых элементов успешной реализации современных интенсивных технологий возделывания сельскохозяйственных культур является своевременное и качественное выполнение комплекса операций по химической обработке посевов. В предлагаемой статье рассмотрена возможность использования в технологическом процессе производства средств малой авиации для проведения химобработок, оценены преимущества и недостатки данного метода. Обоснованы параметры эффективной эксплуатации специализированных самолетов «Фермер-3», выполнена их экономическая оценка по сравнению с классическими средствами механизации, применяемыми в хозяйствах Республики Беларусь
Differential cross section and analysing power of the quasi-free pn -> {pp}_s pi- reaction at 353 MeV
In order to establish links between p-wave pion production in nucleon-nucleon
collisions and low energy three-nucleon scattering, an extensive programme of
experiments on pion production is currently underway at COSY-ANKE. The final
proton pair is measured at very low excitation energy, leading to an S-wave
diproton, denoted here as {pp}_s. By using a deuterium target we have obtained
data on the differential cross section and analysing power of the quasi-free
pol{p}n -> {pp}_s pi^- reaction at 353 MeV. The spectator proton p_sp was
either measured directly in silicon tracking telescopes or reconstructed using
the momentum of a detected pi^-. Both observables can be described in terms of
s-, p-, and d-wave pion production amplitudes. Taken together with the
analogous data on the pol{p}p -> {pp}_s pi^0 reaction, full partial wave
decompositions of both processes were carried out.Comment: The interested reader should also study the paper on pizero
production by D.Tsirkov et al., which has also been submitted to the arXi
Coupled-channel effective field theory and proton-Li scattering
We apply the renormalisation group (RG) to analyse scattering by short-range
forces in systems with coupled channels. For two S-wave channels, we find three
fixed points, corresponding to systems with zero, one or two bound or virtual
states at threshold. We use the RG to determine the power countings for the
resulting effective field theories. In the case of a single low-energy state,
the resulting theory takes the form of an effective-range expansion in the
strongly interacting channel. We also extend the analysis to include the
effects of the Coulomb interaction between charged particles. The approach is
then applied to the coupled Li and Be channels which couple to
a state of Be very close to the Be threshold. At
next-to-leading order, we are able to get a good description of the Li
phase shift and the Be(n,p)Li cross section using four parameters.
Fits at one order higher are similarly good but the available data are not
sufficient to determine all five parameters uniquely.Comment: 22 pages, 2 figures, RevTeX4, typos corrected, accepted for
publication in European Physical Journal
Determination of the scalar polarizabilities of the proton using beam asymmetry in Compton scattering
The scalar dipole polarizabilities, and , are
fundamental properties related to the internal dynamics of the nucleon. The
currently accepted values of the proton polarizabilities were determined by
fitting to unpolarized proton Compton scattering cross section data. The
measurement of the beam asymmetry in a certain kinematical range
provides an alternative approach to the extraction of the scalar
polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured
for Compton scattering below pion photoproduction threshold for the first time.
The results are compared with model calculations and the influence of the
experimental data on the extraction of the scalar polarizabilities is
determined.Comment: 6 pages, 5 figure
The role of nucleon recoil in low-energy antikaon-deuteron scattering
The effect of the nucleon recoil for antikaon-deuteron scattering is
investigated in the framework of effective field theory. In particular, we
concentrate on the calculation of the nucleon recoil effect for the
double-scattering process. It is shown that the leading correction to the
static term that emerges at order xi^{1/2} with xi=M_K/m_N vanishes due to a
complete cancellation of individually large contributions. The resulting recoil
effect in this process is found to be of order of 10-15% as compared to the
static term. We also briefly discuss the application of the method in the
calculations of the multiple-scattering diagrams.Comment: 16 pages, 4 figure
Thermoregulation in colonies of africanized and hybrids with Caucasian, Italian and Carniolan Apis mellifera honey bees
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