# Heavy Holographic Exotics: Tetraquarks as Efimov States

## TL;DR

This paper models non-strange multiquark exotics, especially tetraquarks, as topological molecules in a holographic framework, revealing Efimov states for heavy-flavor configurations and unbound states for hidden-flavor ones.

## Contribution

It introduces a holographic approach to describe multiquark exotics as topological molecules, highlighting Efimov states in heavy-flavor tetraquarks and contrasting with unbound hidden-flavor states.

## Key findings

- Heavy-flavor tetraquarks form Efimov states as bound topological molecules.
- Hidden-flavor tetraquarks are unbound in this model.
- Binding results from a balance between dipole attraction and fermionic repulsion.

## Abstract

We provide a holographic description of non-strange multiquark exotics as compact topological molecules by binding heavy-light mesons to a tunneling configuration in D8-D$\bar 8$ that is homotopic to the vacuum state with 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 $QQ\bar q\bar q$ and $\bar Q\bar Q qq$, emerge as bound Efimov states in a degenerate multiplet $IJ^\pi=(00^+ , 01^+)$ with opposite intrinsic Chern-Simons numbers $\pm \frac 12$. The hidden-flavor tetraquark exotics such as $Q\bar Q q\bar q$, $QQ\bar Q\bar q$ and $QQ\bar Q\bar Q$ as compact topological molecules are unbound. Other exotics are also discussed.