[en] A systematic field theoretic formalism for treating Fermionic resonances with non zero width is given. The implication of unitarity to coupling constants of non local interactions is shown. The extension of the formalism to Bosonic resonance field operators is straight forward. (author)

[en] pp → ppπ⁰ and pp → ppη were considered close to threshold. The pion production was found not only to be dominated by IA and rescattering contributions, but also strongly by box-diagrams, resonances and heavy-meson exchanges. New relevant contributions for the IA were found. The role of the offshell behaviour of nucleon-resonance couplings (P₁₁(1440), S₁₁(1535)) and of interference effects for the eta production was investigated. The results opened a large door for microscopic understanding of short range physics. A covariant model for pp → ppη being under construction is going to be finished. (author)

[en] The on shell description of Initial and Final State Interactions (ISI and FSI) of threshold meson production reactions is reviewed. Existing on shell models and their off shell extension are discussed. Unitarity constraints on enhancement factors are formulated. A strategy for the treatment of essential singularities connected to Coulomb-like FSI is given. (author)

[en] On the basis of a new method for the derivation of the effective action the nonperturbative concept of 'dynamical generation' is explained. A non-trivial, non-Hermitian and PT-symmetric solution for Wightman's scalar field theory in four dimensions is dynamically generated, rehabilitating Symanzik's precarious φ⁴-theory with a negative quartic coupling constant as a candidate for an asymptotically free theory of strong interactions. Finally it is shown making use of the dynamical generation that a Symanzik-like field theory with scalar confinement for the theory of strong interactions can be even suggested by experiment. (author)

[en] The fascinating physics underlying η and η^' mesons can be studied theoretically and experimentally in various contexts. In this presentation we want to turn our attention to two important uncorrelated aspects of this vivid research field which provide yet unexpected challenges or surprises. First we discuss open questions in the theoretical treatment of Coulomb-interaction in the context of reaction processes like pp → ppη. Then we review η-η^' and σ (600) - F₀ (980) mixing in the U (3) x U (3) Linear Sigma Model and extract information on η-η^' mixing and K₀ (800) resonance from meson-meson scattering (Author)

[en] We investigate the exclusive proton-induced K⁺ production near the kaon threshold. Compared are two models: a meson-exchange model, which includes π, ρ, K and K^* exchange, together with the dominant baryon resonances, and a quark-gluon model, where momentum sharing is provided via the exchange of two gluons. Based on covariant bound state wave functions for the meson and the baryons - which we treat as quark-diquark objects - first results for the pp→ pΛK⁺ total cross section are presented for both models. (author)

[en] Light constituent quark masses and the corresponding dynamical quark masses are determined by data, the Quark-Level Linear σ Model, and infrared QCD (quantum chromodynamics). This allows to define effective non-strange and strange current quark masses which reproduce the experimental pion and kaon masses very accurately, by simple additivity. Moreover, the masses of the light scalar mesons σ(600) and κ(800) can be obtained straightforwardly from the constituent quark masses. In contrast, the usual nonstrange and strange current quark masses employed by Chiral Perturbation Theory do not allow a simple quantitative explanation of the pion and kaon masses. (authors)

[en] The quark-level linear σ model (LσM) is employed to compute a variety of electromagnetic and weak observables of light mesons, including pion and kaon form factors and charge radii, charged-pion polarizabilities, semileptonic weak K_l3 decay, semileptonic weak radiative pion and kaon form factors, radiative decays of vector mesons, and nonleptonic weak K_2π decay. The agreement of all these predicted observables with experiment is striking. In passing, the tight link between the LσM and vector-meson dominance is shown. (author)

[en] By comparing SU (3)-breaking scales of linear mass formulae, it is shown that the lowest vector, axial-vector, and scalar mesons all have a q-barq configuration, while the ground-state octet and decuplet baryons are qqq. Also, the quark-level linear σ model is employed to predict similar q-barq and qqq states. Finally, the approximate mass degeneracy of the scalar a0(980) and f0(980) mesons is demonstrated to be accidental

[en] Low-energy meson-meson scattering data are a powerful testing ground for quark models. Here, we describe the behaviour at threshold of S-wave scattering-matrix singularities. The majority of the full scattering-matrix mesonic poles stem from an underlying confinement spectrum. However, the light scalar mesons K₀*(830), a0(980), f0(400-1200), and f0(980) do not, but instead originate in 3P0-barrier semi-bound states. We show that the behaviour of the corresponding poles is identical at threshold. In passing, the light-meson sector is given a firm basis