Classical solutions for exotic instantons?

TL;DR

This paper investigates whether certain exotic brane instantons in string theory can be understood as classical solutions, proposing a connection to eight-dimensional SO(8) instantons and analyzing their properties within the non-abelian D7 brane action.

Contribution

It introduces a novel interpretation of exotic D-brane instantons as classical solutions related to SO(8) instantons in eight dimensions, expanding understanding of their field-theoretical significance.

Findings

Proposes the SO(8) instanton as a classical limit of exotic instantons.

Shows the quartic term of the D7 action is finite on the SO(8) solution.

Verifies the next order term vanishes, ensuring a consistent limit.

Abstract

We consider the D7/D(--1) system in Type I' as a prototypical "exotic" brane instanton. With respect to systems such as the D3/D(-1) ones, which correspond to gauge instantons in four dimensions, exotic systems lack the bosonic mixed moduli w of the ADHM construction, related to the instanton size, and their possible field-theoretical interpretation as classical solutions is an important open question. For the system at hand, we propose that it corresponds to the point-like limit of the eight-dimensional so-called SO(8) instanton solution. This configuration is a solution of the quartic term of the non-abelian D7 action, i.e., the term which stays finite in the limit in which alpha' goes to zero with the string coupling fixed that preserves the D(-1) effects. As a necessary consistency condition, we check that the next order term in the non-abelian effective action vanishes on the SO(8) solution so that the limit we take is well-defined.