Gauge and gravitational instantons: From 3-forms and fermions to Weak Gravity and flat axion potentials

Understand

We investigate the role of gauge and gravitational instantons in the context of the Swampland program.

• Our focus is on the global symmetry breaking they induce, especially in the presence of fermions.
• We first recall and make more precise the description of the dilute instanton gas through a 3-form gauge theory.
• In this language, the familiar suppression of instanton effects by light fermions can be understood as the decoupling of the 3-form.