S-folds, String Junctions, and 4D $\mathcal{N} = 2$ SCFTs

TL;DR

This paper develops a method to determine flavor symmetries and representations in 4D $\\ ext{N}=2$ SCFTs involving S-folds, extending orientifold techniques to non-perturbative string junctions and incorporating discrete torsion effects.

Contribution

It introduces a general procedure for analyzing flavor symmetries in 4D $\mathcal{N}=2$ SCFTs with S-folds, including cases with discrete torsion, and extends F-theory definitions in this context.

Findings

Derived flavor symmetry algebras depend on discrete torsion presence.

Provided a method to read off admissible flavor representations.

Extended F-theory framework to include S-folds with discrete torsion.

Abstract

S-folds are a non-perturbative generalization of orientifold 3-planes which figure prominently in the construction of 4D $\mathcal{N} = 3$ SCFTs and have also recently been used to realize examples of 4D $\mathcal{N} = 2$ SCFTs. In this paper we develop a general procedure for reading off the flavor symmetry experienced by D3-branes probing 7-branes in the presence of an S-fold. We develop an S-fold generalization of orientifold projection which applies to non-perturbative string junctions. This procedure leads to a different 4D flavor symmetry algebra depending on whether the S-fold supports discrete torsion. We also show that this same procedure allows us to read off admissible representations of the flavor symmetry in the associated 4D $\mathcal{N} = 2$ SCFTs. Furthermore this provides a prescription for how to define F-theory in the presence of S-folds with discrete torsion.