Tetraquarks, hadronic molecules, meson-meson scattering and disconnected contributions in lattice QCD

Understand

There are generally two types of Wick contractions in lattice QCD calculations of a correlation function --- connected and disconnected ones.

• The disconnected contribution is difficult to calculate and noisy, thus it is often neglected.
• In the context of studying tetraquarks, hadronic molecules and meson-meson scattering, we show that whenever there are both connected and singly disconnected contractions, the singly disconnected part gives the leading order contribution, and thus should never be neglected.
• As an explicit example, we show that information about the scalar mesons sigma, f0(980), a0(980) and kappa will be lost when neglecting the disconnected contributions.