IR divergences

But the main message is that the IR divergences can never tell you that a physical theory is inconsistent: they just tell you that the IR, long-distance physics may be different than you expected (or than you wanted to see). Production of soft photons in QED and confinement in QCD (and marginally also in conformal theories) are two examples of infrared effects you have to be careful about. But they will never allow you to throw away a theory as an inconsistent one.

— Regularization and renormalization

— Lubos Motl

2013.05.27 Monday ACHK