Moore, GHarris, JNelson, Philip CSinger, I2023-05-232023-05-231986-10-012017-04-26https://repository.upenn.edu/handle/20.500.14332/43243The vacuum amplitude of the heterotic string in a flat background vanishes for the first twenty orders of string perturbation theory. The proof relies on the algebraic geometry of modular forms.Physical Sciences and MathematicsPhysicsArticle