The use of SU(3) chiral perturbation theory in the analysis of low energy meson-baryon interactions is discussed. It is emphasized that short distance effects, arising from propagation of Goldstone bosons over distances smaller than a typical hadronic size, are modeldependent and can lead to a lack of convergence in the SU(3) chiral expansion if they are included in loop diagrams. In this paper we demonstrate how to remove such effects in a chirally consistent fashion by use of a cutoff and demonstrate that such removal ameliorates problems which have arisen in previous calculations due to large loop effects.

We calculate the electric dipole moments of the neutron and the ⌳ within the framework of heavy baryon chiral perturbation theory. They are induced by strong CP-violating terms of the effective Lagrangian in the presence of the vacuum angle 0 . The construction of such a Lagrangian is outlined and we are able to give an estimate for 0 .

The photoproduction and electroproduction of the ,Ј mesons on nucleons are investigated within a relativistic chiral unitary approach based on coupled channels. The s-wave potentials for electroproduction and meson-baryon scattering are derived from a chiral effective Lagrangian, which includes Ј as an explicit degree of freedom and incorporates important features of the underlying QCD Lagrangian such as the axial U͑1͒ anomaly. The effective potentials are iterated in a Bethe-Salpeter equation and the cross sections for ,Ј photoproduction and electroproduction from nucleons are obtained. The results for the Ј photoproduction cross section on protons reproduce the appearance of an S 11 resonance around 1.9 GeV observed at ELSA. The inclusion of electromagnetic form factors increases the predicted electroproduction cross sections on the proton, providing a qualitative explanation for the hard form factor of the photocoupling amplitude observed at CLAS.

We investigate the decays of π 0 , η and η ′ into two photons in an effective U (3) chiral Lagrangian approach without employing large N c arguments. Tree level and one-loop contributions from the anomalous Wess-Zumino-Witten Lagrangian are calculated and the importance of η-η ′ mixing is discussed. Unitarity corrections beyond one-loop play an important role for the decays with off-shell photons and are included by employing a coupled channel Bethe-Salpeter equation which satisfies unitarity constraints and generates vector-mesons from composed states of two pseudoscalar mesons.

The decays η, η ′ → π + π − γ are investigated within an approach that combines oneloop chiral perturbation theory with a coupled channel Bethe-Salpeter equation which satisfies unitarity constraints and generates vector mesons dynamically from composite states of two pseudoscalar mesons. It is furthermore shown that the inclusion of the η ′ as a dynamical degree of freedom does not renormalize the Wess-Zumino-Witten term.