The meson spectra beyond a $q\bar q$ description
  Despite the apparent simplicity of meson spectroscopy there are some states which cannot be accommodated in the usual $q\bar q$ structure. Among them there are either exotic states as the X(1600), or the recently measured charmed states $D_{sJ}^*$ and some of the light scalar mesons. We present a description of the light scalar mesons in terms of $q\bar q$ and $qq\bar q\bar q$ components. 
J. Vijande, F. Fernandez and A. Valcarce