Calculable e^{-1/\lambda} Effects

TL;DR

This paper investigates non-perturbative e^{-1/λ} effects in four-dimensional N=4 superstring theory, linking them to D-brane instantons and validating conjectures about R^4 couplings through duality and one-loop computations.

Contribution

It identifies and evaluates a class of non-perturbative amplitudes in N=4 superstring theory, connecting them to D-brane effects and confirming conjectures about instanton-induced couplings.

Findings

e^{-1/λ} contributions correspond to D-brane instantons

Exact one-loop results match non-perturbative effects

Supports conjecture on D-instanton R^4 couplings

Abstract

We identify and evaluate a class of physical amplitudes in four-dimensional N=4 superstring theory, which receive, in the weak coupling limit, contributions of order e^{-1/\lambda}, where \lambda is the type II superstring coupling constant. They correspond to four-derivative \Ftilde_1 interaction terms involving the universal type II dilaton supermultiplet. The exact result, obtained by means of a one-loop computation in the dual heterotic theory compactified on T^6, is compared with the perturbation theory on the type II side, and the e^{-1/\lambda} contributions are associated to non-perturbative effects of Euclidean solitons (D-branes) wrapped on K3 x T^2. The ten-dimensional decompactification limit on the type IIB side validates the recent conjecture for the D-instanton-induced R^4 couplings.