Of CP and other Gauge Symmetries in String Theory

TL;DR

This paper argues that CP symmetry is a gauge symmetry in string theory, implying it cannot be explicitly broken and that CP violation arises spontaneously, making all CP-violating parameters in principle calculable.

Contribution

It demonstrates that CP is a gauge symmetry in string theory, leading to the conclusion that CP violation must be spontaneous, not explicit, and all related parameters are calculable.

Findings

CP cannot be explicitly broken in string theory

All CP-violating parameters are spontaneous and calculable

String theory provides a framework where theta angles arise from spontaneous CP violation

Abstract

We argue that \CP is a gauge symmetry in string theory. As a consequence, \CP cannot be explicitly broken either perturbatively or non-pertubatively; there can be no non-perturbative \CP-violating parameters. String theory is thus an example of a theory where all $\theta$ angles arise due to spontaneous \CP violation, and are in principle calculable.