Null-state quotient of a string
= Null-state quotient of a string
{title2=$\mathcal H_{\mathrm{phys}}/\operatorname{rad}\mathcal H_{\mathrm{phys} }$}
The physical state space of <old covariant quantization> is quotiented by its physical spurious states, which are orthogonal to all physical states. In a ghost-free sector these form the radical of the semidefinite inner product. The quotient retains positive physical polarizations.