The tetraquark potential and flip-flop in SU(3) lattice QCD

We quantitatively study the tetraquark (4Q) potential $V_{\rm 4Q}$ for the QQ-$\rm \bar{Q}\bar{Q}$ system in SU(3) lattice QCD with $\beta=6.0$ and $16^3 \times 32$ at the quenched level. For about 60 different patterns of 4Q systems, $V_{\rm 4Q}$ is extracted from the 4Q Wilson loop with the smearing method to enhance the ground-state component. When QQ and $\rm \bar{Q}\bar{Q}$ are well separated, $V_{\rm 4Q}$ is found to be expressed as the sum of the one-gluon-exchange Coulomb term and multi-Y type linear term based on the flux-tube picture. When the nearest quark and antiquark pair is spatially close, the system is described as a "two-meson" state. We observe a flux-tube recombination called as "flip-flop" between the connected 4Q state and the "two-meson" state around the level-crossing point