Mirror anomaly in fermionic topological orders

Abstract

We study general 2D fermionic topological orders enriched by the mirror symmetry with M^{2}=1. It is known that certain mirror symmetry enriched fermionic topological orders (mirror SETs) are anomalous, in the sense that they cannot be realized in strict two dimensions but have to live on the surface of 3D topological crystalline superconductors. Mirror anomaly, or equivalently 3D topological crystalline superconductor, has a Z_{16} classification. In this work, we derive an explicit expression, namely, an anomaly indicator, for the Z_{16} mirror anomaly for general fermionic mirror SETs. This derivation is based on the recently developed folding approach, originally proposed for bosonic topological orders. We generalize it to fermion systems. Through this approach, we establish a direct bulk-boundary correspondence between surface fermionic topological orders and 3D bulk topological crystalline superconductors. In addition, during the derivation, we obtain some general properties of fermionic topological orders as well as a few constraints on the properties of fermionic mirror SETs.