Spacetime states of the NSR string, from worldsheet states?

Question

Consider the spectrum of the open NSR string in the Ramond sector. The ground state is fermionic since the Fourier coefficients of the oscillators satisfy a Clifford algebra. We can construct ``ladder'' operators from these creation and annihilation operators in the usual way. This furnishes an 8-dimensional representation of the Clifford algebra (16 x 16 Dirac matrices).

I have read that the worldsheet vacuum, and in fact all the 16 states in the state space of the worldsheeet, also give rise to states in the spacetime theory (i.e. the second-quantized version) but not all states of the spacetime theory correspond to states in the worldsheet theory. Why does the latter happen?

Is there an example of a spacetime state that does not correspond to a worldsheet state?

This post imported from StackExchange Physics at 2015-04-17 12:33 (UTC), posted by SE-user leastaction