Covariant tetraquark equations in quantum field theory

We derive exact yet practical covariant equations of quantum field theory describing a tetraquark in terms mix four-quark states $2q2\overline{q}$, and two-quark $q\overline{q}$. A feature our approach is that it avoids the overcounting problems usually plague formulations few-body (the only exception being two-body Bethe-Salpeter equation). This achieved by coupling $2q2\overline{q}$ to $q\overline{q}$ through use model operators contract $q\overline{q}$-irreducible Green function down kernel. Although chosen current work describes dynamics meson-meson diquark-antidiquark states, derived have form exact, as all corrections due particular are taken into account well-defined special four-point amplitude $\mathrm{\ensuremath{\Delta}}$ entering equations. The agreement with those obtained previously consideration disconnected interactions; however, despite more general, they been here much simpler transparent way.