Superstring BRST no-ghost theorem at arbitrary picture number
  A simple and self-contained treatment of the superstring BRST no-ghost theorem at non-zero momentum and arbitrary picture number is presented. We prove by applying the spectral sequence that the absolute BRST cohomology is isomorphic to two copies of the light-cone spectrum at adjacent ghost numbers. We single out a representative in each cohomology class. A non-degenerate pairing between the Fock spaces, an induced pairing on the cohomology and a Hermitian inner product on the cohomology are constructed. 
Mykola Dedushenko
hep-th math-ph math.MP