D-brane Instantons in Type II String Theory

TL;DR

Blumenhagen et al. survey D-brane instantons in Type II N=1 compactifications, presenting a unified framework for computing non-perturbative corrections to holomorphic couplings, including superpotential, gauge kinetic function, Beasley-Witten terms, and multi-instanton effects. They cover zero-mode structures, flux lifting, quiver theories, and geometric transitions, with checks against RG cascades and string dualities. They discuss phenomenological applications to neutrino masses, μ-term, Yukawas, and SUSY breaking, highlighting how stringy instantons generate otherwise forbidden couplings. The review also discusses poly-instantons and the remaining theoretical challenges toward a complete, globally consistent non-perturbative D-brane instanton calculus.

Abstract

We review recent progress in determining the effects of D-brane instantons in N=1 supersymmetric compactifications of Type II string theory to four dimensions. We describe the abstract D-brane instanton calculus for holomorphic couplings such as the superpotential, the gauge kinetic function and higher fermionic F-terms. This includes a discussion of multi-instanton effects and the implications of background fluxes for the instanton sector. Our presentation also highlights, but is not restricted to the computation of D-brane instanton effects in quiver gauge theories on D-branes at singularities. We then summarize the concrete consequences of stringy D-brane instantons for the construction of semi-realistic models of particle physics or SUSY-breaking in compact and non-compact geometries.

Figures (8)

• Figure 1: Disc diagram for charged zero mode absorption.
• Figure 2: Annulus 1-loop vacuum diagram.
• Figure 3: Extended quiver diagram showing the matter fields and the instanton zero modes for $SU(N_c)$ SQCD with $N_f$ flavors.
• Figure 4: Annulus diagram for an ${\cal E}$-instanton correction to the gauge coupling of a stack of ${\cal D}_a$ branes. The upper indices give the ghost number of the vertex operators.
• Figure 5: Quiver diagram for the ${\mathbb Z}_2$ orbifold of the conifold, for arbitrary numbers of fractional and regular D3-branes. We have labeled bifundamentals according to the parent field in the un-orbifolded conifold theory.