The Geometry of Fractional Branes

TL;DR

This paper constructs the effective action and classical geometry of fractional D-branes in type IIA string theory, revealing a naked singularity and the limitations of perturbative gauge coupling descriptions.

Contribution

It provides a detailed derivation of the low-energy effective action and classical background for fractional branes using boundary state techniques, highlighting the enhancon mechanism.

Findings

Classical geometry is valid outside the enhancon sphere.

The background contains a naked singularity of repulson type.

The gauge coupling's one-loop behavior breaks down at the enhancon radius.

Abstract

By looking at fractional Dp-branes of type IIA on T_4/Z_2 as wrapped branes and by using boundary state techniques we construct the effective low-energy action for the fields generated by fractional branes, build their world-volume action and find the corresponding classical geometry. The explicit form of the classical background is consistent only outside an enhancon sphere of radius r_e, which encloses a naked singularity of repulson-type. The perturbative running of the gauge coupling constant, dictated by the NS-NS twisted field that keeps its one-loop expression at any distance, also fails at r_e.