Molecular structures in charmonium spectrum: The $XYZ$ puzzle
  We study in the framework of a constituent quark model the possible contributions of molecular structures to the XYZ charmonium like states. We analyze simultaneously the $c\bar{c}$ structures and the possible molecular components in a formalism which allows us to treat channels below and above thresholds. The only molecular state found in the $1^{++}$ sector correspond to the X(3872). Molecular resonances also appear with other quantum numbers. So, the so called Y(3940) and the X(3915) are suggested to be $J^{PC}=0^{++}$ charmonium states. In the $J^{PC}=1^{--}$ sector we also found significant contributions of the molecular structures which can affect the phenomenology. 
P. G. Ortega, D. R. Entem and F. Fernandez
hep-ph nucl-th