Exploring the regime of strong gauge-field backreaction during axion inflation

Axion inflation is a well-motivated inflationary model with many fascinating phenomenological consequences mainly originating from helical gauge-field production. The gauge fields can impact scalar perturbations, induce the production of circularly polarized gravitational waves or even seed cosmological magnetic fields. Even fermions can be produced from strong electromagnetic fields via the Schwinger effect. During my talk, I will present the gradient expansion formalism, an elegant technique to efficiently determine the background dynamics of the axion--gauge-field system in the regime of strong gauge-field backreaction. I will discuss two applications for this tool, studying if strong gauge-field production can cause enough friction to ensure long-lasting slow-roll dynamics, and determining the impact of Schwinger pair production onto gauge-field production.