Doubly-heavy baryons, tetraquarks, and related topics

Abstract

We review the physics of doubly-heavy baryons $QQq$ and tetraquarks $QQ\bar{q}\bar{q}$. For the latter, the stability is reached for large enough mass ratio $M/m$, even when spin forces and color mixing are neglected. It is thus customarily claimed that $bb\bar{q}\bar{q}$ in its ground state cannot decay into $b\bar{q}+b\bar{q}$. In some model, $cc\bar{u}\bar{d}$ is shown to be stable if color mixing and spin effects are properly taken into account. It is conjectured that some $bc\bar{q}{\bar{q}}^{\prime }$ benefits from favorable adjustments of the gluon tubes in the confinement regime. Some recent studies of pentaquarks and hexaquarks are also summarized.

Comments: To appear in the Proc. of the Workshop "Double-Charm Baryons and Dimesons", Bled (Slovenia), June 17-23, 2018, ed. M.~Rosina et al