Speaker
Description
We study axion dynamics and relic abundance in first-order phase transitions, extending the bubble misalignment mechanism to a cosmological setting. In this setup, the axion mass turns on discontinuously inside expanding true vacuum bubbles. We perform lattice simulations of the axion field and identify two regimes. For fast transitions, the dynamics reduces to delayed misalignment, where the onset of oscillations is set by the percolation time. For slower transitions, bubble-induced spatial gradients reduce the effective oscillation amplitude inside bubbles. We construct a semi-analytic description that captures both regimes and reproduces the simulation results. We further quantify the impact on isocurvature perturbations, the small-scale power spectrum, and axion minicluster formation.