Mass spectrum of the J^P=1/2^- and 3/2^- pentaquark antidecuplets in the perturbative chiral quark model

We study the recently discovered Theta^+ baryon in the context of the perturbative chiral quark model. The basic configuration of the Theta^+ is set up as a pentaquark bound state, where the single particle wave functions are the ground state solutions of a confining potential. We classify the resulting pentaquark multiplets as the J^P=1/2^- and 3/2^- flavor SU(3) antidecuplet. The full mass spectrum of the multiplets is determined by including meson and gluon cloud contributions inducing flavor SU(3) breaking. Mainly due to the semi-perturbative gluon effects the resulting 3/2^- antidecuplet is about 185 MeV heavier than the 1/2^- one. We assign the observed Theta^+ baryon as a member of the 1/2^- antidecuplet and discuss in particular the relation to the recent experimental signal for a Xi^{--} baryon.