Chiral perturbation theory for pentaquark baryons and its applications

We construct a chiral Lagrangian for pentaquark baryons assuming that the recently found Θ+(1540) state belongs to an antidecuplet of SU(3) flavor symmetry with JP=12±. We derive the Gell-Mann-Okubo formulae for the antidecuplet baryon masses, and a possible mixing between the antidecuplet and the pentaquark octet. Then we calculate the cross sections for π−p→K−Θ+ and γn→K−Θ+ using our chiral Lagrangian. The resulting amplitudes respect the underlying chiral symmetry of QCD correctly. We also describe how to include the light vector mesons in the chiral Lagrangian.