Abstract

Between November 1974, when the J/\psi particle was discovered, until 2003, when the X(3872) resonance was described by the Belle Collaboration, the quarkonium spectrum was satisfactorily described by naive quark models. However, the exploration of energies above the D\bar D threshold has led to the appearance of unexpected states, the so-called XYZ states, difficult to accommodate in the naive picture of a q\bar q bound states.

A common feature among all these exotic states is the presence of nearby two particle thresholds. This coincidence reinforces the intuition that the residual interaction between such two particles can form a molecular state. The description of this type of structures is very tricky from a theoretical point of view because the strength of the residual interaction is usually model dependent and one can generate spurious states if this interaction is not under control.

In this talk I will review the state of meson-meson and baryon-meson molecules calculations, using a constituent quark model that has been applied to a wide range of hadronic observables, and therefore all model parameters are completely constrained.