A dual quark model is developed from the usual Veneziano model by explicitly including the Dirac spin of the quarks. Resonances appear without the parity doubling and new ghosts present in previous models with spin. This is accomplished by eliminating the contributions of the negative parity components (MacDowell-twins) of the spin quarks 1/2 through the introduction of fixed J-plane cuts. Theresonances belong to an SU6 symmetric spectrum identical, on theleading trajectory, with that of the usual static symmetrical quarkmodel. All resonances couple via SU6w x O2Lz symmetric verticesand the model factorizes with essentially the same degeneracy as theusual Veneziano model. As a consequence of requiring these two features the model acquires further new structure which is studiedin detail in terms of the asymptotic behavior of the model. This new structure leads to unavoidable "background" contributions to the imaginary parts of the amplitudes not present in previous dual models.This situation is examined and interpreted in the language of Finite Energy Sum Rules.
In order to test the basic features of the model explicit calculations are made for the case of pion-nucleon scattering in the Regge limit. To make the numerical work easier a somewhat simplified version of the model is used. Although the results ofthe calculations are suggestive of reasonable J-plane structure for the various amplitudes, i.e., the location of Regge pole-fixed cut interference is reasonable from the standpoint of the data, the overall kinematic behavior of the amplitudes is definitely not compatible with what is measured. However, it is noted that this kinematic behavior depends strongly on those details of the model which were simplified in the present study. If such models are tobe unambiguously and successfully tested against data, future studies must treat these details more completely and realistically, including both unitarity and symmetry breaking effects.
