Pseudovector versus pseudoscalar coupling in kaon photoproduction - revisited

The question of pseudovector versus pseudoscalar coupling schemes for the kaon-hyperon-nucleon interaction is re-examined for the reaction $\gamma p\to K^+ \Lambda$ in several isobaric models. These models typically include Born terms, $K^*$- and $K_1$-exchange in the t-channel, and a few different combinations of spin-1/2 baryon resonances in the $s$- and $u$-channels. The coupling constants are obtained by fitting to a large data set. We find that both pseudoscalar and pseudovector couplings can allow for a satisfactory description of the present database. The resulting coupling constants, $g_{K\Lambda N}$ and $g_{K\Sigma N}$, in the pseudovector coupling scheme are smaller than those predicted using flavor SU(3) symmetry, but consistent with the values obtained in a QCD sum rule calculation.