Speaker
Description
Axion inflation with a Chern-Simons coupling to gauge fields provides a well-motivated and phenomenologically rich realization of the early universe. The rolling axion tachyonically amplifies one gauge helicity, and for sufficiently large coupling this production becomes strong enough to back react on the axion background resulting in a non-linear axion evolution. In this work, we develop a semi-analytical description of the homogeneous axion dynamics that follows the system continuously from weak to strong backreaction. We derive a simple effective equation of motion for the axion zero mode that incorporates the delayed gauge response and provides a unified description of the homogeneous evolution from weak to strong backreaction. This formulation captures both the onset of backreaction and the subsequent approach from unstable to a stable Anber Sorbo type attractor branch. We show that this stable regime is consistent with recent analytical and numerical approaches, and identify the conditions controlling the transition between the weak and strong backreaction regimes. We then use this homogeneous treatment as a foundation for extending the model to inhomogeneous axion perturbations, with the goal of understanding how local nonlinear dynamics modifies the evolution.