Effects of D-instantons

TL;DR

This paper investigates nonperturbative effects of D-instantons in type IIB superstring theory, revealing explicit instanton corrections to effective interactions, and explores their implications for string scattering and duality symmetries.

Contribution

It provides a detailed analysis of D-instanton contributions to superstring effective actions and proposes a conjectured SL(2,Z) completion for certain interactions.

Findings

Explicit nonperturbative D-instanton corrections to $R^4$ interactions.

D-instanton spectrum deduced via T-duality and multiply-wound states.

Proposed SL(2,Z) invariance of the corrected effective interactions.

Abstract

Scattering of fundamental states of type IIB supergravity and superstring theory is discussed at low orders in perturbation theory in the background of a D-instanton. The integration over fermionic zero modes in both the low energy supergravity and in the string theory leads to explicit nonperturbative terms in the effective action. These include a single instanton correction to the known tree-level and one-loop $R^4$ interactions. The `spectrum' of multiply-charged D-instantons is deduced by T-duality in nine dimensions from multiply-wound world-lines of marginally-bound D-particles. This, and other clues, lead to a conjectured SL(2,Z) completion of the $R^4$ terms which suggests that they are not renormalized by perturbative corrections in the zero-instanton sector beyond one loop. The string theory unit-charged D-instanton gives rise to point-like effects in fixed-angle scattering, raising unresolved issues concerning distance scales in superstring theory.