Lattice investigation of the tetraquark candidates a0(980) and kappa
  It is a long discussed issue whether light scalar mesons have sizeable four-quark components. We present an exploratory study of this question using N_f=2+1+1 twisted mass lattice QCD. A mixed action approach ignoring disconnected contributions is used to calculate correlator matrices consisting of mesonic molecule, diquark-antidiquark and two-meson interpolating operators with quantum numbers of the scalar mesons a0(980) (1(0^++)) and kappa (1/2(0+)). The correlation matrices are analyzed by solving the generalized eigenvalue problem. The theoretically expected free two-particle scattering states are identified, while no additional low lying states are observed. We do not observe indications for bound four-quark states in the channels investigated. 
Jan Oliver Daldrop, Constantia Alexandrou, Mattia Dalla Brida, Mario   Gravina, Luigi Scorzato, Carsten Urbach, Marc Wagner
hep-lat