Superstring theory

Definition

A superstring theory is a string theory in which the worldsheet theory has supersymmetry. In the Ramond–Neveu–Schwarz formulation, the worldsheet fields are the following.

1. Bosonic fields $X^\mu$, $\mu = 0, \dots, D-1$, which give the embedding of the worldsheet into spacetime, as in the Polyakov action.
2. Fermionic fields $\psi^\mu$, two-dimensional Majorana spinors on the worldsheet with one spacetime vector index.
3. A local worldsheet supersymmetry that exchanges $X^\mu$ and $\psi^\mu$.

The quantum theory is consistent, free of anomalies, only for $D = 10$. A projection of the spectrum, the GSO projection, removes the tachyon and makes the spacetime spectrum supersymmetric.