The quantum superstring as a WZNW model with N=2 superconformal symmetry

We present a new development in our approach to the covariant quantization of superstrings in 10 dimensions which is based on a gauged WZNW model. To incorporate worldsheet diffeomorphisms we need the quartet of ghosts (b_zz,c^z, β_zz, γ^z) for topological gravity. The currents of this combined system form an N=2 superconformal algebra. The model has vanishing central charge and contains two anticommuting BRST charges, Q_S=Q_W+∮γ ^zb_zz and Q_V=∮c^z (T^W_zz+ (1/2)T^top_zz)+γ ^z(B^W _zz+(1/2)B^top _zz-(1/2)c^z F_zzz-(1/4)γ ^zΦ_zzz). Physical states form the cohomology of Q_S+Q_V+∮η _z, where η_z is obtained by the usual fermionization of β_zz,γ^z, have non-negative grading, and are annihilated by b₀ and β₀. We no longer introduce any ghosts by hand, and the formalism is completely Lorentz covariant.