Consider a 2D *gapped* CSL with a *nonzero* Chern number $m$, then is the GSD of the system on a torus directly related to the Chern number $m$?

For example, see this article, in the last paragraph on page 7, the authors give the **4-fold GSD** from the Chern number $m=\pm2$ for a CSL. I can not understand the explanation, can anybody present an intuitive illustration or a simple mathematical proof ? I will be very appreciated, thank you very much.

This post imported from StackExchange Physics at 2014-03-09 08:38 (UCT), posted by SE-user K-boy