String Perturbation Theory Around Dynamically Shifted Vacuum

Understand

In some string theories, e.g.

• SO(32) heterotic string theory on Calabi-Yau manifolds, a massless field with a tree level potential can acquire a tachyonic mass at the one loop level, forcing us to quantize the theory around a new background that is not a solution to the classical equations of motion and hence is not described by a conformally invariant world-sheet theory.
• We describe a systematic procedure for carrying out string perturbation theory around such backgrounds.