Tachyon condensation in magnetic compactifications

TL;DR

This paper studies tachyon condensation in magnetic compactifications of type I string theory, showing it restores supersymmetry and leads to a unique stable vacuum with specific gauge symmetry breaking.

Contribution

It demonstrates that tachyon condensation in magnetic compactifications restores supersymmetry and identifies the resulting vacuum with a known 8d superstring theory.

Findings

Tachyon condensation restores supersymmetry broken by magnetic flux.

The gauge group SO(32) breaks to USp(16).

The resulting vacuum matches a known 8d superstring theory.

Abstract

Intersecting D-brane models and their T-dual magnetic compactifications provide an attractive framework for particle physics, allowing for chiral fermions and supersymmetry breaking. Generically, magnetic compactifications have tachyons that are usually removed by Wilson lines. However, quantum corrections prevent local minima for Wilson lines. We therefore study tachyon condensation in the simplest case, the magnetic compactification of type I string theory on a torus to eight dimensions. We find that tachyon condensation restores supersymmetry, which is broken by the magnetic flux, and we compute the mass spectrum of vector- and hypermultiplets. The gauge group $\text{SO}(32)$ is broken to $\text{USp}(16)$. We give arguments that the vacuum reached by tachyon condensation corresponds to the unique 8d superstring theory already known in the literature, with discrete $B_{ab}$ background or, in the T-dual version, the type IIB orientifold with three $\text{O}7_-$-planes, one $\text{O}7_+$-plane and eight D7-branes coincident with the $\text{O}7_+$-plane. The ground state after tachyon condensation is supersymmetric and has no chiral fermions.