Exotic Spectroscopy: A Lattice QCD perspective

We review recent results for exotic states with beauty quarks from Lattice QCD, focusing on heavy-light tetraquarks. In particular, there is a growing consensus of deeply-bound, strong-interaction stable $T_{bb}$ and $T_{bbs}$ four-quark states. Beyond these the possibility of further bound states where either the light quarks are made heavier, or the heavy quarks lighter are being explored, such as possible $T_{bc}$ and $T_{bs}$ bound states. We also compare predictions for positive-parity $B_s$-mesons, which, in analogy to the $D_{s0}^*(2317)$ and $D_{s1}(2460)$, may feature a large four-quark component. We conclude by briefly discussing searches for other heavy multi-quark states.