Physical States in the $W_3$ String
  We present a review of some of the recent developments in the study of the $W_3$ string. One of the interesting features of the theory is that the physical spectrum includes states with non-standard ghost structure, such as excitations of the ghost fields, both for discrete-momentum and continuous-momentum states. (Contribution to the Proceedings of the 16'th Johns Hopkins Workshop on Current Problems in Particle Physics, Gothenburg, Sweden, June 1992) 
C.N. Pope