Decoupling A and B model in open string theory -- Topological adventures in the world of tadpoles

TL;DR

This paper demonstrates that including unorientable diagrams in open topological string theory ensures consistent decoupling of A and B models across all genera, linking tadpole cancellation to D-brane and orientifold charge cancellation.

Contribution

It provides a microscopic proof of A and B model decoupling in open superstring theory and explicitly computes one-loop amplitudes using Ray-Singer torsions.

Findings

Decoupling of A and B models is guaranteed at all genera.

Explicit one-loop amplitude calculations in the B-model.

Holomorphic anomaly equations derived for open topological strings.

Abstract

In this paper we analyze the problem of tadpole cancellation in open topological strings. We prove that the inclusion of unorientable worldsheet diagrams guarantees a consistent decoupling of A and B model for open superstring amplitudes at all genera. This is proven by direct microscopic computation in Super Conformal Field Theory. For the B-model we explicitly calculate one loop amplitudes in terms of analytic Ray-Singer torsions of appropriate vector bundles and obtain that the decoupling corresponds to the cancellation of D-brane and orientifold charges. Local tadpole cancellation on the worldsheet then guarantees the decoupling at all loops. The holomorphic anomaly equations for open topological strings at one loop are also obtained and compared with the results of the Quillen formula.