Residues and World-Sheet Instantons

TL;DR

This paper demonstrates that certain Calabi-Yau heterotic string compactifications are stable under world-sheet instanton effects due to a residue theorem, and extends these results to M-theory membrane instantons.

Contribution

It introduces a residue theorem explaining instanton cancellations in (0,2) sigma models and applies it to stability analysis in heterotic and M-theory compactifications.

Findings

Residue theorem explains instanton cancellations in (0,2) models.

Heterotic compactifications on the quintic are stable under instantons.

Superpotential contributions from M-theory membrane instantons are computed.

Abstract

We reconsider the question of which Calabi-Yau compactifications of the heterotic string are stable under world-sheet instanton corrections to the effective space-time superpotential. For instance, compactifications described by (0,2) linear sigma models are believed to be stable, suggesting a remarkable cancellation among the instanton effects in these theories. Here, we show that this cancellation follows directly from a residue theorem, whose proof relies only upon the right-moving world-sheet supersymmetries and suitable compactness properties of the (0,2) linear sigma model. Our residue theorem also extends to a new class of "half-linear" sigma models. Using these half-linear models, we show that heterotic compactifications on the quintic hypersurface in CP^4 for which the gauge bundle pulls back from a bundle on CP^4 are stable. Finally, we apply similar ideas to compute the superpotential contributions from families of membrane instantons in M-theory compactifications on manifolds of G_2 holonomy.