Heavy holographic exotics: Tetraquarks as Efimov states

Abstract

We provide a holographic description of nonstrange multiquark exotics as compact topological molecules by binding heavy-light mesons to a tunneling configuration in $\mathrm{D}8\text{\ensuremath{-}}\mathrm{D}\overline{8}$ that is homotopic to the vacuum state with a fixed Chern-Simons number. In the tunneling process, the heavy-light mesons transmute to fermions. Their binding is generic and arises from a trade-off between the dipole attraction induced by the Chern-Simons term and the U(1) fermionic repulsion. In the heavy quark limit, the open-flavor tetraquark exotics $QQ\overline{q}\overline{q}$ and $\overline{Q}\overline{Q}qq$ emerge as bound Efimov states in a degenerate multiplet $I{J}^{\ensuremath{\pi}}=(0{0}^{+},0{1}^{+})$ with opposite intrinsic Chern-Simons numbers $\ifmmode\pm\else\textpm\fi{}\frac{1}{2}$. The hidden-flavor tetraquark exotics such as $Q\overline{Q}q\overline{q}$, $QQ\overline{Q}\overline{q}$, and $QQ\overline{Q}\overline{Q}$ as compact topological molecules are unbound. Other exotics are also discussed.