Dyon Loops and Abelian Instantons

I will discuss field configurations of Abelian gauge fields that carry second Chern number, generated by closed monopole worldlines in four-dimensional Euclidean space. These are "Abelian Instantons" that ascribe physical significance of the electromagnetic vacuum angle. I will discuss the connection between these and traditional Yang-Mills instantons. Time permitting, I will speculate on the existence of Abelian instantons in the context of electromagnetism minimally coupled to gravity.