Molecular interpretation of the XYZ states

Departamento de Física Teórica and IFIC, Centro Mixto Universidad de Valencia-CSIC, Institutos de Investigación de Paterna, Aptdo. 22085, 46071 Valencia, Spain

^a e-mail: molina@rcnp.osaka-u.ac.jp

Abstract

We study the vector – vector system including all the possible channels with quantum numbers charm = 0, strangeness = 0 around the energy region of 4000 MeV. New states with hidden charm around 4000MeV have been discovered by the B factories. They are intriguingly close to the $D^{*}{\overline{D}}^{*}$ and $D_s^{*}{\overline{D}}_s^{*}$ thresholds and do not have the properties of the charmonium states.We study the possible formation of $D^{*}{\overline{D}}^{*}$ and $D_s^{*}{\overline{D}}_s^{*}$ bound states in the framework of the Hidden Gauge formalism and discuss some of the models that favor the molecular assumption of some XYZ states: The hidden gauge formalism, Heavy baryon Chiral Perturbation Theory and the compositeness condition of Weinberg.