Reading between the lines of four-dimensional gauge theories

Understand

Starting with a choice of a gauge group in four dimensions, there is often freedom in the choice of magnetic and dyonic line operators.

• Different consistent choices of these operators correspond to distinct physical theories, with the same correlation functions of local operators in R^4.
• In some cases these choices are permuted by shifting the theta-angle by 2pi.
• In other cases they are labeled by new discrete theta-like parameters.