Structure and compositeness of exotic hadrons

It is remarkable that recent experimental developments unveil the existence of many candidates of exotic hadrons, such as multiquarks, hadronic molecules, gluon hybrids, and so on. However, theoretical interpretation of the structure of a specific state is not always converged. In this talk, we introduce the compositeness of hadrons as a quantitative measure of the internal structure. In particular, the difficulty of determining the structure of unstable resonances is discussed in detail. We present several attempts to relate the compositeness to the observable quantities. Finally, we evaluate the compositeness of physical exotic hadrons, and discuss their internal structure.

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