The Low-level Spectrum of the $W_3$ String
  We investigate the spectrum of physical states in the $W_3$ string theory, up to level 2 for a multi-scalar string, and up to level 4 for the two-scalar string. The (open) $W_3$ string has a photon as its only massless state. By using screening charges to study the null physical states in the two-scalar $W_3$ string, we are able to learn about the gauge symmetries of the states in the multi-scalar $W_3$ string. 
H. Lu, B.E.W. Nilsson, C.N. Pope, K.S. Stelle and P.C. West