Experimental supressions of resonance couplings as gauge-like conditions from dual resonance models

The paper deals with the observed phenomenon of dynamical suppression of a number of resonance couplings [f′(1520)ππ, $K^{**}\left(1420\right)K\eta$, etc.], new instances of which keep appearing as data accumulate. A few of such effects have been conventionally understood in terms of the quark model, which is however inadequate to account for all of them. We consider a specific dual-resonance model, which is suggested by the approximate linearity in the (s, t, u) plane observed for the zero trajectories of certain two-body amplitudes. Relevant experimental evidence concerning zero behavior has been already discussed elsewhere; we present here a short and updated review of it. We show that such a dual model predicts in a natural way many of the observed coupling suppressions, and possibly---once generalized---all of them. It also accounts partially, in an analogous manner, for the decoupling of exotic resonances. The way in which the dual constraints of the model and the resonance decouplings are interrelated exhibits a structural similarity with the well-known interconnection between charge conservation and decoupling of longitudinal photons in electromagnetic interactions. The model is supposed to apply in its present form only to amplitudes in which linearity of zeros is observed, but there are elements to argue that dual constraints of the same nature are active in any hadronic amplitude. Central in obtaining the results is the interplay of the dual model and unitary symmetries, which is much stronger than in conventional dual models, where such symmetries intervene only externally through Chan-Paton factors.