Non-interacting \textit{KN} contribution in the QCD sum rule for the pentaquark $\Theta ^{+}$ (1540)

We perform a QCD sum rule analysis for the pentaquark baryon $\Theta ^{+}$ with the non-interacting \textit{KN} contribution treated carefully. The coupling of the $\Theta ^{+}$ current to the \textit{KN} state is evaluated by applying the soft kaon theorem and vacuum saturation. When using a five-quark current including scalar and pseudo-scalar diquarks, the\textit{ KN }contribution turns out not to be very important and the previous result of the negative parity $\Theta ^{+}$ is reproduced again. The Borel analysis of the correlation function for $\Theta ^{+}$ with the \textit{KN} continuum states subtracted yields the mass of the J$^{P}$= 1/2$^{-} \quad \Theta ^{+}$ around 1.5 GeV.