[en] 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 πN 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 D₁₃ poles and their crossed poles, as well as π, μ, 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_πNN, 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

[en] Motivated by new, upcoming Brookhaven data, pion scattering and pion-induced eta production on the nucleon in the S₁₁(1535) resonance region is studied in an extension of the unitary, relativistic resonance model by Surya and Gross. The Kernel of the relativistic wave equation includes the nucleon, Roper, δ(1232), D₁₃(1520) and S₁₁(1535) pole terms along with contact σ- and ρ-like exchange terms. The formalism includes a coupling between the πN and ηN channels. The resonance parameters are adjusted to reproduce the experimental πN phase shifts

[en] The E2/M1 ratio is found to be -3.1%. This ratio is calculated by using the new relativistic resonance model for pion-photoproduction on a single nucleon [1]. The model is both unitary and gauge invariant to all orders of the strong coupling g_π. This model is also consistent with the πN scattering model that has been developed earlier and that describes final state interactions [2]. copyright 1995 American Institute of Physics

[en] This paper presents the history of the competition First Step to Nobel Prize in Physics organized by Poland, its development from a national workshop in 1991/92 to an international competition nowadays and its organization, as well as the results obtained by the participants.

[en] The analysis of the light-cone two-body bound-state equation is extended to the scattering problem. The rotational invariance is violated in the light-cone quantization method when the Fock space is truncated for practical calculations. Using a simple scalar field model, we investigate the explicit rotation dependence of the two-body scattering phase shifts in the light-cone quantization approach. We find the regions of coupling constant and c.m. momentum where the rotation dependence in the phase shift is negligible. We also make a connection of our analysis with the light-cone scattering formalism recently presented by Fuda

[en] Pion nucleon scattering up to 600 MeV laboratory kinetic energy is described by a manifestly covariant wave equation in which the pion is restricted to its mass shell. The kernel of the equation includes nucleon (N), Roper (N^*), delta (Δ), and D₁₃ poles, with their corresponding crossed pole terms approximated by contact interactions, and contact σ- and ρ-like exchange terms. The πNN vertex is treated as a mixture of γ⁵ and γ^μγ⁵ coupling, with a mixing parameter λ chosen so that the dressed nucleon pole will be unshifted by the interaction. Chiral symmetry is maintained at threshold. The resonance contributions are fully unitarized by the equation, with their widths determined by the dynamics included in the model. The Δ and D₁₃ are treated as pure spin 3/2 particles, with no spin 1/2 amplitude in the S channel. The complete development of this model, which gives a very good fit to all the data up to 600 MeV, is presented

[en] A review is made of the relativistic bound state problem formulated on the light cone. The relation between the light cone bound state equation and Bethe-Salpeter equation is discussed, and QCD quark distribution amplitudes are related to the short distance hadron wavefunctions. The generalization to a multiquark system is also demonstrated in a toy dibaryon analysis

[en] 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 πN interactions consistent with the covariant, unitary, resonance model of πN scattering previously developed. The kernel of the equation includes nucleon (N), Roper (N^*), delta (Δ), and D₁₃ poles and their crossed poles, as well as π, ρ, and ω exchange terms. The Kroll-Rudermann term and other interaction currents ensure that the model is exactly gauge invariant to all orders in the strong coupling g_πNN. The threshold value of the E₀₊ amplitude is in good agreement with recent estimates obtained from chiral perturbation theory. Elastic unitarity to first order in the charge e (Watson theorem) is maintained up to the two-pion production threshold. The complete development of this model, which gives a good fit to all L≤2 multiples up to 770 MeV, is presented. copyright 1996 The American Physical Society

[en] We discuss the two-pion-exchange (TPE) potential which emerges from a box diagram with one nucleon (the spectator) restricted to its mass shell, and the other nucleon line replaced by a subtracted, covariant πN scattering amplitude which includes Δ, Roper, and D₁₃ isobars, as well as contact terms and off-shell (nonpole) dressed nucleon terms. The πN amplitude satisfies chiral symmetry constraints and fits πN data below ∼ 700 MeV pion energy. We find that this TPE potential can be well approximated by the exchange of an effective sigma and delta meson, with parameters close to the ones used in one-boson-exchange models that fit NN data below the pion production threshold. copyright 1996 The American Physical Society

[en] A brief report on the final round of the first World Physics Olympiad (WoPhO) held in Lombok, West Nusa Tenggara, Indonesia is presented. The theoretical and experimental problems are presented and the mark distribution is discussed. (paper)