Anisotropic lattice QCD studies of penta-quarks and tetra-quarks
  Anisotropic lattice QCD studies of penta-quarks(5Q) with J^P=1/2^\pm and 3/2^{\pm} are presented at the quenched level together with tetra-quarks(4Q). The standard gauge action at \beta=5.75 and O(a) improved quark (clover) action with \kappa=0.1410(0.010)0.1440 are employed on the anisotropic lattice with the renormalized anisotropy a_s/a_t = 4. The ``hybrid boundary condition(HBC)'' is adopted to discriminate a compact resonance state from scattering states. Only massive 5Q states are found for J^P=1/2^+ and 3/2^{\pm}, which cannot be identified as \Theta^+(1540). A low-lying 5Q state is found for J^P=1/2^- at m_{5Q}\simeq 1.75 GeV, which however turns out to be an NK scattering state through the HBC analysis. A preliminary result for 4Q states is presented suggesting an existence of a compact 4Q resonance at m_{4Q} \simeq 1.1 GeV in the idealized SU(4)_f chiral limit. 
N.Ishii (Univ. of Tokyo), T.Doi (RIKEN BNL), H.Iida (Tokyo Inst.   Tech), M.Oka (Tokyo Inst. Tech), F.Okiharu (Nihon Univ.),...