One-loop masses of Neumann-Dirichlet open strings and boundary-changing vertex operators

Understand

We derive the masses acquired at one loop by massless scalars in the Neumann-Dirichlet sector of open strings, when supersymmetry is spontaneously broken.

• It is done by computing two-point functions of "boundary-changing vertex operators" inserted on the boundaries of the annulus and M\"obius strip.
• This requires the evaluation of correlators of "excited boundary-changing fields," which are analogous to excited twist fields for closed strings.
• We work in the type IIB orientifold theory compactified on $T^2\times T^4/\mathbb{Z}_2$, where $\mathcal{N}=2$ supersymmetry is broken to $\mathcal{N}=0$ by the Scherk-Schwarz mechanism implemented along $T^2$.