**GSO (Gliozzi-Scherk-Olive) projection** is an ingredient used in constructing a consistent model in superstring theory. The projection is a selection of a subset of possible vertex operators in the worldsheet conformal field theory (CFT)—usually those with specific worldsheet fermion number and periodicity conditions. Such a projection is necessary to obtain a consistent worldsheet CFT.

For terminology, for a compact 1-manifold as a $S^1$ circle, there are two spin structures, let one be periodic or antiperiodic in going around the circle. In string theory, these are called

of spin structures.

For the projection to be consistent, the set $A$ of operators retained by the projection must satisfy:

Closure — The operator product expansion (OPE) of any two operators in $A$ contains only operators which are in $A$.

Mutual locality — There are no branch cuts in the OPE of any two operators in the set $A$.

Modular invariance — The partition function on the two-torus of the theory containing only the operators in $A$ respects modular invariance.

My naive question is that

Whether there is a **mathematical branch** highly relevant for formulating **GSO (Gliozzi-Scherk-Olive) projection** and determine the *consistency of projection*?

My guess is that the "Modular invariance," "Closure" and "Mutual locality" may have something to do with the **symplectic geometry and Lagrangian submanifolds (of certain space)**. But I am not sure what is the precise mathematics to put these ideas together?

This post imported from StackExchange MathOverflow at 2019-07-09 21:58 (UTC), posted by SE-user wonderich