# Hadronic molecules

## TL;DR

This paper reviews the evidence, theoretical frameworks, and methods used to identify and study hadronic molecules, which are bound states of hadrons analogous to light nuclei, especially in the heavy quarkonium sector.

## Contribution

It provides a comprehensive overview of experimental evidence, effective field theories, lattice QCD results, and analysis techniques for hadronic molecules, highlighting recent advances and challenges.

## Key findings

- Experimental candidates for hadronic molecules are identified.
- Nonrelativistic effective field theories are effective for studying these structures.
- Lattice QCD results support the existence and properties of hadronic molecules.

## Abstract

A large number of experimental discoveries especially in the heavy quarkonium sector that did not at all fit to the expectations of the until then very successful quark model led to a renaissance of hadron spectroscopy. Among various explanations of the internal structure of these excitations, hadronic molecules, being analogues of light nuclei, play a unique role since for those predictions can be made with controlled uncertainty. We review experimental evidences of various candidates of hadronic molecules, and methods of identifying such structures. Nonrelativistic effective field theories are the suitable framework for studying hadronic molecules, and are discussed in both the continuum and finite volumes. Also pertinent lattice QCD results are presented. Further, we discuss the production mechanisms and decays of hadronic molecules, and comment on the reliability of certain assertions often made in the literature.