Gauge field production and Schwinger reheating in runaway axion inflation

In a class of (pseudoscalar) inflation, inflationary phase is followed by a kination phase, where the Universe is dominated by the kinetic energy of the inflaton that runs away in a vanishing scalar potential. In this class of postinflationary evolution of the Universe, reheating of the Universe cannot be achieved by the inflaton particle decay, which requires its coherent oscillation in a quadratic potential. In this study, we explore the U(1) gauge field production through the Chern-Simons coupling between the pseudoscalar inflaton and the gauge field during the kination era and examine the subsequent pair-particle production induced by the amplified gauge field known as the Schwinger effect, which can lead to reheating of the Universe. We find that with a rough estimate of the Schwinger effect for the Standard Model hyper U(1) gauge field and subsequent thermalization of the pair-produced particles, a successful reheating of the Universe can be achieved by their eventual domination over the kinetic energy of the inflaton, with some reasonable parameter sets. This can be understood as a concrete realization of the ???Schwinger reheating???. Constraints from the later-time cosmology are also discussed.

Automated summary

By studying the Chern-Simons coupling between the pseudoscalar inflaton and the gauge field, and examining the subsequent pair-particle production induced by the amplified gauge field known as the Schwinger effect during the kination era, we find that successful reheating of the Universe can be achieved through the domination of the pair-produced particles over the kinetic energy of the inflaton.