 No-ghost theorem for the critical bosonic string

In flat 26-dimensional bosonic string theory, at ordinary nonzero momentum, take physical string states satisfying $L_{n>0}|\psi ⟩=0$ and $(L_0-1)|\psi ⟩=0$. The inner product restricted to these states is positive semidefinite. Quotienting by physical null string states removes the degeneracy; the resulting Hilbert space is represented by the 24 transverse string oscillators. This is a statement about negative-norm matter states, not about removing the auxiliary Faddeev-Popov ghosts. It does not remove the bosonic tachyon.