Axion interactions with Domain and Bubble Walls - Isabel Garcia Garcia (U. Washington)

Abstract: I will discuss the effect of interactions between two-dimensional defects like bubble and domain walls and axion-like particles whose decay constant changes across the interface. This class of interactions are naturally present in theories featuring axions and other scalar degrees of freedom, and qualitatively differ from those mediated by a change in mass. When an axion hits a wall across which its decay constant changes, the onset of exponentially small reflection probability can be parametrically delayed well into the relativistic regime. This results in a transient force on the interface proportional to $\gamma^2$, with $\gamma$ the relative Lorentz factor.
We explore the broader consequences of this effect for expanding bubble and domain walls in the early universe that interact with a background field of either frozen or oscillating axions. Possible implications include modifications to the dynamics of bubble walls during a first-order phase transition, as well as the generation of a relativistic component of axions.