SU3Symmetry and the Existence of a Ninth Vector Meson

Baryon-baryon and baryon-antibaryon interactions are discussed within the framework of the $S{U}_3$-symmetric octet model without assuming $R$ invariance. Although this model, at least in the present version, contains a free parameter in the specification of the baryon-vector meson coupling, it turns out that the predictions of the model are not consistent with the experimental determinations of the baryon-vector meson coupling constants, if only exchanges of members of the vector meson octet are considered. As the simplest way of removing such discrepancy, the presence of a ninth vector meson is proposed, a unitary singlet, for which some experimental support is available.