Non-Perturbative Effects on a Fractional D3-Brane

TL;DR

This paper investigates non-perturbative effects on a fractional D3-brane, revealing instanton-induced superpotentials, condensates, and couplings that influence the effective four-dimensional theory, especially under supersymmetry breaking.

Contribution

It demonstrates how D-brane instantons generate superpotentials and other couplings in the presence of fractional D3-branes and fluxes, extending understanding of non-perturbative effects in string theory.

Findings

Superpotential and fermionic condensate generated by instantons.

Instanton effects induce non-perturbative contributions to the cosmological constant.

New couplings arise in the effective action under supersymmetry breaking fluxes.

Abstract

In this note we study the N=1 abelian gauge theory on the world volume of a single fractional D3-brane. In the limit where gravitational interactions are not completely decoupled we find that a superpotential and a fermionic bilinear condensate are generated by a D-brane instanton effect. A related situation arises for an isolated cycle invariant under an orientifold projection, even in the absence of any gauge theory brane. Moreover, in presence of supersymmetry breaking background fluxes, such instanton configurations induce new couplings in the 4-dimensional effective action, including non-perturbative contributions to the cosmological constant and non-supersymmetric mass terms.