Softly Broken MQCD and the Theta Angle

TL;DR

This paper explores how the microscopic theta angle affects non-supersymmetric MQCD five-brane configurations, revealing spectral flow, level-crossing, and spontaneous CP symmetry breaking, akin to phase transitions in theta.

Contribution

It provides new insights into the dependence of MQCD vacua on the theta angle and demonstrates phenomena similar to 't Hooft's phase transitions within this framework.

Findings

Spectral flow of the vacua curves with changing theta

Level-crossing indicating phase transition points

Spontaneous CP symmetry breaking at specific theta values

Abstract

We consider a family of non-supersymmetric MQCD five-brane configurations introduced by Witten, and discuss the dependence of the curves on the microscopic theta angle and its relation with CP. We find evidence for a non-trivial spectral flow of the curves (vacua) and for the level-crossing of adjacent curves at a particular value of the theta angle, with spontaneous breaking of CP symmetry, providing an MQCD analogue of the phase transitions in theta proposed by 't Hooft.