Geometric foundations of classical Yang–Mills theory

We analyze the geometric foundations of classical Yang–Mills theory by studying the relationships between internal relativity, locality, global/local invariance, and background independence. We argue that internal relativity and background independence are the two independent defining principles of Yang–Mills theory. We show that local gauge invariance—heuristically implemented by means of the gauge argument—is a direct consequence of internal relativity. Finally, we analyze the conceptual meaning of BRST symmetry in terms of the invariance of the gauge fixed theory under general local gauge transformations.