  We study s-wave bound states of a hadron and a light pseudoscalar meson
induced by the Weinberg-Tomozawa (WT) interaction in the flavor SU(3) symmetric
limit. The WT interaction is a driving force to generate quasibound states
dynamically in the chiral unitary approaches. The strength and sign of the WT
interaction are determined only by the group theoretical structure of the
target hadrons, and we present a general expression of the strengths for the
flavor SU(3) case. We show that, for the channels which are more exotic than
the target, the interaction is repulsive in most cases, and the strength of the
attractive interaction is universal for any possible target states. We
demonstrate that the attractive coupling is not strong enough to generate an
exotic state from the physically known masses of target hadrons. In addition,
we also find a nontrivial Nc dependence of the coupling strengths. We show that
the channels which are attractive at Nc=3 changes into repulsive ones for large
Nc, and, therefore, no attractive interaction exists in exotic channels in the
large-Nc limit.
