Notes on discrete torsion in orientifolds

TL;DR

This paper explores discrete torsion in orientifolds, applying group actions on B fields to recover known results and derive new phase factors for nonorientable worldsheets and C fields.

Contribution

It extends the understanding of discrete torsion in orientifolds by deriving new phase factors and connecting group cohomology with twisted equivariant K theory.

Findings

Recovered old results on group cohomology and K theory

Derived phase factors for nonorientable worldsheets

Established analogues for C fields in orientifold contexts

Abstract

In this short note we discuss discrete torsion in orientifolds. In particular, we apply the physical understanding of discrete torsion worked out several years ago, as group actions on B fields, to the case of orientifolds, and recover some old results of Braun and Stefanski concerning group cohomology and twisted equivariant K theory. We also derive new results including phase factors for nonorientable worldsheets and analogues for C fields.