CRITICAL AND NONCRITICAL W(2,4) STRINGS

Nilpotent BRST operators for higher-spin W2,s strings, with currents o f spins 2 and s, have recently been constructed for s = 4, 5 and 6. In the case Of W2,4, this operator can be understood as being the BRST o perator for the critical WB2 String. In this paper, we construct a gen eralized BRST operator that can be associated with a non-critical W2,4 string, in which WB2 matter is coupled to the WB2 gravity of the crit ical case. We also obtain the complete cohomology of the critical W2,4 BRST operator, and investigate the physical spectra of the s = 5 and s = 6 string theories.