  We study light scalar mesons with particular focus on the a_0(980) using
lattice QCD with 2+1+1 dynamical quark flavors. To investigate the structure of
these scalar mesons and to identify, whether a sizeable tetraquark component is
present, we use a large set of operators, including diquark-antidiquark,
mesonic molecule and two-meson operators. We find that the low-lying states
overlap essentially exclusively with two-meson states. This indicates that in
the channels investigated no tightly bound four-quark states of either
molecular or diquark-antidiquark type exist.

High Energy Physics - Lattice