Coisotropic D8-branes and Model-building

TL;DR

This paper introduces coisotropic D8-branes in type IIA string theory, showing they can generate chiral spectra and superpotentials, expanding the toolkit for string model-building beyond traditional D6-branes.

Contribution

It demonstrates the role of coisotropic D8-branes with fluxes in creating chiral models and superpotentials, providing explicit examples and new MSSM-like vacua.

Findings

Coisotropic D8-branes induce D6-brane charge via fluxes.

They generate chiral spectra at intersections.

New MSSM-like vacua are constructed using D8- and D6-branes.

Abstract

Up to now chiral type IIA vacua have been mostly based on intersecting D6-branes wrapping special Lagrangian 3-cycles on a CY three-fold. We argue that there are additional BPS D-branes which have so far been neglected, and which seem to have interesting model-building features. They are coisotropic D8-branes, in the sense of Kapustin and Orlov. The D8-branes wrap 5-dimensional submanifolds of the CY which are trivial in homology, but contain a worldvolume flux that induces D6-brane charge on them. This induced D6-brane charge not only renders the D8-brane BPS, but also creates D=4 chirality when two D8-branes intersect. We discuss in detail the case of a type IIA Z2 x Z2 orientifold, where we provide explicit examples of coisotropic D8-branes. We study the chiral spectrum, SUSY conditions, and effective field theory of different systems of D8-branes in this orientifold, and show how the magnetic fluxes generate a superpotential for untwisted Kahler moduli. Finally, using both D6-branes and coisotropic D8-branes we construct new examples of MSSM-like type IIA vacua.