HET Seminar | Abelian Instantons in Quantum Field Theory and Gravity

I will discuss field configurations of Abelian gauge fields that carry non-zero second Chern number, generated by closed monopole worldlines in four-dimensional Euclidean space. These "Abelian instantons" render the electromagnetic vacuum angle physical. In the presence of gravity, magnetic monopoles that are Reissner-Nordstrom black holes naturally realize these field configurations. Including these instantons in the gravitational path integral makes the electromagnetic theta-term a physical parameter of the Standard Model coupled to gravity,