Superspace Effective Actions for 4D Compactifications of Heterotic and Type II Superstrings

TL;DR

This paper develops a new supersymmetric description of 4D compactified superstrings, revealing novel couplings of the dilaton and implications for quantum corrections in effective actions.

Contribution

It introduces a manifestly spacetime supersymmetric sigma model for 4D superstring compactifications, clarifying dilaton couplings and loop corrections in the effective action.

Findings

Dilaton couples differently in heterotic and Type II models.

Hypermultiplet interactions can receive non-perturbative corrections.

Vector multiplet interactions are protected from quantum corrections.

Abstract

Two-dimensional sigma models are defined for the new manifestly spacetime supersymmetric description of four-dimensional compactified superstrings. The resulting target-superspace effective action is constrained by the way the spacetime dilaton couples to the worldsheet curvature: For the heterotic superstring, the worldsheet curvature couples to the real part of a chiral multiplet, and for Type II it couples to the real part of the sum of a vector multiplet and a tensor hypermultiplet. For the Type II superstring, this contradicts the standard folklore that only a hypermultiplet counts string-loops, explains the peculiar dilaton coupling of Ramond-Ramond fields, and allows the effective action to be easily written in N=2 4D superspace. It also implies that vector multiplet interactions get no quantum corrections, while hypermultiplet interactions can only get corrections if mirror symmetry is non-perturbatively broken.