On the phase diagram of the discrete $Z_6$ spin models
  We point out some problems with the previously-proposed phase diagram of the $Z_6$ spin models. Consideration of the diagram near to the decoupling surface using both exact and approximate arguments suggests a modification which remedies these deficiencies. With the aid of a new parametrisation of the phase space, we study the models numerically, with results which support our conjectures. 
Patrick Dorey, Paolo Provero, Roberto Tateo and Stefano Vinti