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D-brane, fluxes and chirality

Angel M. Uranga

TL;DR

The paper investigates how NS-NS and RR fluxes in type II string theory generate chiral anomalies on D-brane worldvolumes via anomaly inflow, with the key insight that these inflows can be cancelled by explicit flux-induced Wess-Zumino terms rather than by dynamical chiral fermions. This flux-induced mechanism enables four-dimensional chirality in configurations where conventional chiral fermions are absent, and it plays a crucial role in anomaly cancellation for brane probes, compactifications, and model-building scenarios. The work further explores brane-flux transitions that can alter the chiral content by trading dynamical fermions for flux-induced WZ terms, and it discusses global anomalies arising from K-theory considerations. Together, these results offer a distinct, microscopic route to 4D chirality in string theory and connect to tadpole cancellation, Green-Schwarz-type cancelations, and duality-related chirality mechanisms.

Abstract

We describe a topological effect on configurations of D-branes in the presence of NS-NS and RR field strength fluxes. The fluxes induce the appearance of chiral anomalies on lower dimensional submanifolds of the D-brane worldvolume. This anomaly is not associated to a dynamical chiral fermion degree of freedom, but rather should be regarded as an explicit flux-induced anomalous term (Wess-Zumino term) in the action. The anomaly is cancelled by an inflow mechanism, which exploits the fact that fluxes can act as sources of RR fields. We discuss several applications of this flux-induced anomaly; among others, its role in understanding anomaly cancellation in compactifications with D-branes and fluxes, and the possibility of phase transitions where a chiral fermion disappears from the D-brane world-volume spectrum, being replaced by an explicit Wess-Zumino term. We comment on the relation among different mechanisms to obtain four-dimensional chirality in string theory.

D-brane, fluxes and chirality

TL;DR

The paper investigates how NS-NS and RR fluxes in type II string theory generate chiral anomalies on D-brane worldvolumes via anomaly inflow, with the key insight that these inflows can be cancelled by explicit flux-induced Wess-Zumino terms rather than by dynamical chiral fermions. This flux-induced mechanism enables four-dimensional chirality in configurations where conventional chiral fermions are absent, and it plays a crucial role in anomaly cancellation for brane probes, compactifications, and model-building scenarios. The work further explores brane-flux transitions that can alter the chiral content by trading dynamical fermions for flux-induced WZ terms, and it discusses global anomalies arising from K-theory considerations. Together, these results offer a distinct, microscopic route to 4D chirality in string theory and connect to tadpole cancellation, Green-Schwarz-type cancelations, and duality-related chirality mechanisms.

Abstract

We describe a topological effect on configurations of D-branes in the presence of NS-NS and RR field strength fluxes. The fluxes induce the appearance of chiral anomalies on lower dimensional submanifolds of the D-brane worldvolume. This anomaly is not associated to a dynamical chiral fermion degree of freedom, but rather should be regarded as an explicit flux-induced anomalous term (Wess-Zumino term) in the action. The anomaly is cancelled by an inflow mechanism, which exploits the fact that fluxes can act as sources of RR fields. We discuss several applications of this flux-induced anomaly; among others, its role in understanding anomaly cancellation in compactifications with D-branes and fluxes, and the possibility of phase transitions where a chiral fermion disappears from the D-brane world-volume spectrum, being replaced by an explicit Wess-Zumino term. We comment on the relation among different mechanisms to obtain four-dimensional chirality in string theory.

Paper Structure

This paper contains 13 sections, 22 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Chirality from fluxes
  3. The anomaly inflow mechanism
  4. Chirality from fluxes
  5. The inflow
  6. Absence of dynamical chiral fermions
  7. Origin of the anomaly
  8. Applications
  9. Probe analysis of tadpole vs anomaly cancellation
  10. Application to model building
  11. Brane-flux transitions and the fate of chiral fermions
  12. Global gauge anomalies
  13. Origin of chirality in string theory

Figures (1)

  • Figure 1: Anomaly inflow for a) D6-branes intersection over a four-dimensional submanifold of their world-volume; b) D6-brane in the presence of longitudinal $\lambda H_{NS}$ flux.