Stable vs Unstable Vortices in SQCD

TL;DR

This paper classifies stable and unstable vortices in supersymmetric QCD and related theories, revealing conditions for their stability, decay modes, and implications for confinement and baryon formation.

Contribution

It provides a topological classification of vortices in worldvolume theories of M5-branes, generalizing previous classifications and analyzing stability conditions in SQCD.

Findings

Torsion Z_N-strings can be stable when flavor symmetry is gauged.

Nontorsion Z-strings are stable if all colors are locked to flavors.

Unstable string decay modes and lifetimes are identified.

Abstract

We give a topological classification of stable and unconfined massive particles and strings (and some instantons) in worldvolume theories of M5-branes and their dimensional reductions, generalizing Witten's classification of strings in SYM. In particular 4d N=2 SQCD softly broken to N=1 contains torsion (Douglas-Shenker) Z_N-strings and nontorsion (Hanany-Tong) Z-strings. Some of the former are stable when the flavor symmetry is gauged, while those that are not stable confine quarks and in some vacua even dyons into baryons. The nontorsion strings are stable if and only if all colors are locked to flavors, which is weaker than the BPS condition. As a byproduct unstable string decay modes and approximate lifetimes are found. Cascading theories have no vortices stabilized by the topological charges treated here and in particular Gubser-Herzog-Klebanov axionic strings do not carry such a charge.