Heterotic strings and quantum entanglement

We construct & Zopf;(N) orbifolds of the ten-dimensional heterotic string theories appropriate for implementing the stringy replica method for the calculation of quantum entanglement entropy. A novel feature for the heterotic string is that the gauge symmetry must be broken by a Wilson line to ensure modular invariance. We completely classify the patterns of symmetry breaking. We show that the tachyonic contributions in all cases can be analytically continued, with a finite answer in the domain 0 < N <= 1, relevant for calculating entanglement entropy across the Rindler horizon. We discuss the physical implications of our results.