Investigation of the tetraquark candidate $a_0(980)$: technical aspects   and preliminary results
  We discuss technical aspects and first results of a lattice QCD study of the $a_0(980)$ state. We employ various interpolating operators of quark-antiquark, mesonic molecule, diquark-antidiquark and two-meson type. Both connected and disconnected contributions including diagrams with closed fermion loops are computed. To keep statistical errors small, it is essential to optimize the computation of these diagrams by choosing that combination of techniques most appropriate for each type of diagram from the correlation matrix of interpolating operators. We illustrate, how this can be done, by discussing certain diagrams in detail. We also present preliminary results corresponding to a $4\times 4$ submatrix computed with 2+1 flavors of clover fermions. 
Abdou Abdel-Rehim, Constantia Alexandrou, Joshua Berlin, Mattia Dalla   Brida, Mario Gravina, Marc Wagner
hep-lat