Adding flavor to AdS/CFT

TL;DR

This paper explores how adding flavor D-branes in AdS/CFT models captures fundamental quarks' properties, including chiral symmetry and quark mass, within a string theory framework, primarily using supersymmetric examples.

Contribution

It demonstrates that flavor D-branes can be modeled as space-time filling objects with specific properties in AdS, aligning with expectations for quark behavior in dual gauge theories.

Findings

D-branes can end in the UV region to represent massive quarks.

Distinct sets of D-branes encode chiral symmetry.

Probe limit suffices for analyzing key properties.

Abstract

Coupling fundamental quarks to QCD in the dual string representation corresponds to adding the open string sector. Flavors therefore should be represented by space-time filling D-branes in the dual 5d closed string background. This requires several interesting properties of D-branes in AdS. D-branes have to be able to end in thin air in order to account for massive quarks, which only live in the UV region. They must come in distinct sets, representing the chiral global symmetry, with a bifundamental field playing the role of the chiral condensate. We show that these expectations are born out in several supersymmetric examples. To analyze most of these properties it is not necessary to go beyond the probe limit in which one neglects the backreaction of the flavor D-branes.