Hyperons in the Bound State Approach with Vector Mesons

We investigate a model for hyperons based on the bound state approach in which vector mesons are explicitly incorporated. We show that for empirical values of the mesonic parameters the strange hyperon spectrum is well reproduced. We also discuss the extension of the model to heavier flavors. We show that the explicit presence of the heavy vectors leads to good predictions for the heavy baryon masses. † Fellow of the Consejo Nacional de Investigaciones Cient́ıficas y Técnicas. The bound state approach [1] has become a very useful tool for the study of hyperon properties [2]. In this approach strange hyperons are described as solitonkaon bound systems. To find the soliton-kaon interactions one usually starts with an effective chiral lagrangian supplemented with proper chiral symmetry breaking terms. Up to now, most of the calculations have been done using effective lagrangians where only pseudoscalar meson fields were included. There are several reasons to believe, however, that these are not the only degrees of freedom to be taken into account. Within the chiral soliton model vector mesons are known to improve the description of the nucleon properties [3]. Moreover, it has been recently argued [4, 5] that they are of fundamental importance in the extension of the bound state description to heavier flavors. It is now well-known that in the heavy quark limit of QCD the heavy vector meson (i.e. B) becomes degenerate with the heavy pseudoscalar (i.e. B) and therefore should be explicitly included in the effective action [6]. In the past, some attempts have been done to explicitly incorporate vector mesons in the bound state model. In Ref.[7] a model with an explicit ω vector meson was studied. In Ref.[8] although the full nonet of vector mesons was included, the strange vector meson (K) was integrated out before solving the equations of motion. In the present paper we will deal with the full vector meson nonet throughout. In addition, a more general chiral symmetry breaking action that includes derivative-type terms will be used. Finally, although most of this work will be devoted to the description of low-lying positive parity strange hyperons some results for charmed and bottom baryons will also be given. To incorporate vector mesons in the chiral lagrangian we use the hidden gauge approach [9]. This scheme is based on the identification of the “strong” vector mesons as gauge bosons of the hidden gauge symmetry of the non-linear sigma model. The corresponding effective action is given by Γ = Γ0 + Γsb + Γan, (1) where Γ0 is the non-anomalous chirally symmetric contribution to the action