Mirrorfolds with K3 Fibrations

TL;DR

This paper constructs and analyzes a class of non-geometric string vacua called mirrorfolds, based on K3 fibrations and superconformal field theories, revealing stability conditions and properties of D-branes.

Contribution

It introduces a new class of mirrorfold models using K3 fibrations, providing explicit modular invariant partition functions and analyzing their stability and D-brane characteristics.

Findings

Compact K3 mirrorfolds are non-supersymmetric and IR unstable due to tachyon condensation.

Non-compact K3 mirrorfolds can be stable and include both supersymmetric and non-supersymmetric vacua.

In non-compact models, D-branes are always non-BPS and can be stabilized.

Abstract

We study a class of non-geometric string vacua realized as completely soluble superconformal field theory (SCFT). These models are defined as `interpolating orbifolds' of $K3 \times S^1$ by the mirror transformation acting on the $K3$ fiber combined with the half-shift on the $S^1$-base. They are variants of the T-folds, the interpolating orbifolds by T-duality transformations, and thus may be called `mirrorfolds'. Starting with arbitrary (compact or non-compact) Gepner models for the $K3$ fiber, we construct modular invariant partition functions of general mirrorfold models. In the case of compact $K3$ fiber the mirrorfolds only yield non-supersymmetric string vacua. They exhibit IR instability due to winding tachyon condensation which is similar to the Scherk-Schwarz type circle compactification. When the fiber SCFT is non-compact (say, the ALE space in the simplest case), on the other hand, both supersymmetric and non-supersymmetric vacua can be constructed. The non-compact non-supersymmetric mirrorfolds can get stabilised at the level of string perturbation theory. We also find that in the non-compact supersymmeric mirrorfolds D-branes are {\em always} non-BPS. These D-branes can get stabilized against both open- and closed-string marginal deformations.