Relativistic chiral SU(3) symmetry, large N c sum rules and meson-baryon scattering

The relativistic chiral SU(3) Lagrangian is used to describe kaonnucleon scattering imposing constraints from the pion-nucleon sector and the axial-vector coupling constants of the baryon octet states. We solve the covariant coupled-channel Bethe-Salpeter equation with the interaction kernel truncated at chiral order Q 3 where we include only those terms which are leading in the large Nc limit of QCD. The baryon decuplet states are an important explicit ingredient in our scheme, because together with the baryon octet states they form the large Nc baryon ground states of QCD. Part of our technical developments is a minimal chiral subtraction scheme within dimensional regularization, which leads to a manifest realization of the covariant chiral counting rules. All SU(3) symmetry-breaking eects are well controlled by the combined chiral and large Nc expansion, but still found to play a crucial role in understanding the empirical data. We achieve an excellent description of the data set typically up to laboratory momenta of plab ’ 500 MeV.