Decay width of the pentaquark state $\Theta^+(1540)$ with QCD sum rules
  In this article, we take the point of view that the pentaquark state $\Theta^+(1540)$ has negative parity, and choose the diquark-triquark type interpolating current to calculate the strong coupling constant $g_{\Theta NK}$ in the QCD sum rule approach. Our numerical results indicate the values of the strong coupling constant $g_{\Theta NK}$ are very small, $|g_{\Theta NK}|=0.175\pm0.084$, and the width $\Gamma_\Theta <4MeV$, which can explain the narrow width $\Gamma \leq 10 MeV$ naturally. 
Zhi-Gang Wang, Wei-Min Yang, Shao-Long Wan