Pion photoproduction up to 770 MeV photon laboratory energy is described by a manifestly covariant wave equation, which includes a treatment of the final state {pi}N interactions consistent with the covariant, unitary, resonance model of pi-N scattering previously developed. The kernel of the equation includes nucleon (N), Roper (N*), Delta, and D{sub 13} poles and their crossed poles, as well as {pi}, {mu}, and w exchange terms. The Kroll-Ruderman term and other interaction currents insure that the model is exactly gauge invariant to all orders in the strong coupling, g{sub {pi}NN}, and that the low energy theorem is satisfied. Unitarity is maintained up to first order in the charge e (Watson theorem). The complete development of this model, which gives a good fit to all the data up to 770 MeV, is presented.

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Unitary, gauge invariant, relativistic resonance model for pion photoproduction

The deuteron-proton elastic scattering has been studied in the multiple-scattering expansion formalism. Primary attention has been given to such relativistic problems as a deuteron wave function in a moving frame and transformation of spin states due to Wigner rotation. Parametrization of the nucleon—nucleon t matrix has been used to take the off-energy-shell effects into account. The vector, A
 y
 , and tensor, A
 yy
 , analyzing powers of the deuteron have been calculated at two deuteron kinetic energies: 395 and 1200 MeV. The obtained results are compared with the experimental data.

Deuteron-proton elastic scattering at intermediate energies

The properties of the gravito-magnetic interaction in non-stationary conditions are discussed. A direct deduction of the equivalent Faraday?Henry law is given. A comparison is made between gravito-magnetic and electromagnetic induction, and it is shown that there is no Meissner-like effect for superfluids in the field of massive spinning bodies. The impossibility of stationary motions in directions not along the lines of the gravito-magnetic field is found. Finally the results are discussed in relation to the behaviour of superconductors.

Gravito-electromagnetism versus electromagnetism

Low-energy radiative-capture reactions within two-cluster coupled-channel description

Starting from the instant form of relativistic quantum dynamics for a system of interacting fields, where amongst the ten generators of the Poincare group only the Hamiltonian and the boost operators carry interactions, we offer an algebraic method to satisfy the Poincare commutators.We do not need to employ the Lagrangian formalism for local fields with the Noether representation of the generators. Our approach is based on an opportunity to separate in the primary interaction density a part which is the Lorentz scalar. It makes possible apply the recursive relations obtained in this work to construct the boosts in case of both local field models (for instance with derivative couplings and spins ≥ 1) and their nonlocal extensions. Such models are typical of the meson theory of nuclear forces, where one has to take into account vector meson exchanges and introduce meson-nucleon vertices with cutoffs in momentum space. Considerable attention is paid to finding analytic expressions for the generators in the clothed-particle representation, in which the so-called bad terms are simultaneously removed from the Hamiltonian and the boosts. Moreover, the mass renormalization terms introduced in the Hamiltonian at the very beginning turn out to be related to certain covariant integrals that are convergent in the field models with appropriate cutoff factors.

A Possible Way for Constructing Generators of the Poincaré Group in Quantum Field Theory

Positive pion electroproduction from the deuteron near threshold has been considered within an approach based on the unitary transformation method. The gauge independence of the treatment is provided by using an explicitly gauge-independent expression for the reaction amplitude. The results of calculations for the kinematics of the experiments on forward-angle $\pi^ + $
 meson electroproduction accomplished at Saclay and Jefferson Laboratory are discussed and compared with those given by the impulse approximation. It is shown that the observed behaviour of the cross-sections is in accordance with the calculations based on the pion-nucleon dynamics. In particular, the pion production rate suppression in the $^2{\rm H}({\rm e,e}'\pi^ + $
 )nn reaction compared to that for the $^1{\rm H}({\rm e,e}'\pi^ + $
 )n one can be due to such “nuclear medium” effects as nucleon motion and binding along with Pauli blocking in the final nn state.

Nuclear effects in positive pion electroproduction on the deuteron near threshold

The charge exchange reaction $pd\to npp$
 at 1 GeV projectile proton energy is studied in the multiple-scattering expansion technique. This reaction is considered in a special kinematics, when the momentum transfer from the beam proton to the fast neutron is close to zero. The differential cross-section and a set of polarization observables are calculated. It was shown that the contribution of the final-state interaction between two protons is very significant.

Study of deuteron-proton charge exchange reaction at small transfer momentum

Relying upon our previous treatment of the density matrices for nuclei (in general, nonrelativistic self-bound finite systems) we are studying a combined effect of center-of-mass motion and short-range nucleon-nucleon correlations on the nucleon density and momentum distributions in light nuclei (4He and 16O). Their intrinsic ground-state wave functions are constructed in the so-called fixed center-of-mass approximation, starting with mean-field Slater determinants modified by some correlator (e.g., after Jastrow or Villars). We develop the formalism based upon the Cartesian or boson representation, in which the coordinate and momentum operators are linear combinations of the creation and annihilation operators for oscillatory quanta in the three different space directions, and get the own “Tassie-Barker” factors for each distribution and point out other model-independent results. After this separation of the center-of-mass motion effects we propose additional analytic means in order to simplify the subsequent calculations (e.g., within the Jastrow approach or the unitary correlation operator method). The charge form factors, densities and momentum distributions of 4He and 16O evaluated by using the well-known cluster expansions are compared with data, our exact (numerical) results and microscopic calculations.

Translationally invariant calculations of form factors, nucleon densities and momentum distributions for finite nuclei with short-range correlations included

Positive pion electroproduction from the deuteron near threshold has been considered within an approach based on the unitary transformation method. The gauge independence of the treatment is provided by using an explicitly gauge independent expression for the reaction amplitude. The results of calculations for kinematics of the experiments on forward-angle $\pi^+$ meson electroproduction accomplished at Saclay and Jefferson Laboratory are discussed and compared with those given by the impulse approximation. It is shown that the observed behaviour of the cross sections is in accordance with the calculations based on the pion-nucleon dynamics. In particular, the pion production rate suppression in the $^2H(e,e'\pi^+)nn$ reaction compared to that for the $^1H(e,e'\pi^+)n$ one can be due to such ``nuclear medium'' effects as nucleon motion and binding along with Pauli blocking in the final $nn$ state.

The charge-exchange reaction pd->npp at 1 GeV projectile proton energy is studied in the multiple-scattering expansion technique. This reaction is considered in a special kinematics, when the transfer momentum from the beam proton to fast neutron is close to zero. The differential cross section and a set of polarization observables are calculated. It was shown that contribution of the final state interaction between two protons is very significant.

A. V. Shebeko

Papers

Nuclear effects in positive pion electroproduction on the deuteron near threshold

Study of deuteron-proton charge exchange reaction at small transfer momentum

Translationally invariant calculations of form factors, nucleon densities and momentum distributions for finite nuclei with short-range correlations included

Nuclear effects in positive pion electroproduction on the deuteron near threshold

Study of deuteron-proton charge exchange reaction at small transfer momentum