Speaker
Description
Cosmological models featuring QCD axions or axion-like particles (ALPs) can face a serious domain wall (DW) problem when the domain wall number $N_{DW}$, exceeds unity. While biased potentials are a commonly proposed solution, we explore alternative mechanisms based on thermal plasma friction.
Using techniques from nonequilibrium quantum field theory, we evaluate the quantum equations of motion governing the coupled dynamics of domain walls, free axions, and particles in the primordial Standard Model (SM) plasma. This framework enables us to calculate the thermal pressure exerted on a DW moving with velocity v, taking into account all relevant particle interactions and self-interactions that depend on the specifics of the axion model.
We further develop an extended Velocity-dependent One-Scale (VOS) model to describe the evolution of the DW network under the influence of friction. In this context, we also derive analytic expressions for the energy loss due to both scalar radiation and the chopping mechanism and include friction terms arising from interactions with the Standard Model (SM) plasma.
Finally, we examine the implications of our model, establishing bounds and exploring Beyond Standard Model (BSM) signatures subject to these dynamics, such as constraints from Big Bang Nucleosynthesis (BBN), the Stochastic Gravitational Wave Background (SGWB), and CMB birefringence.
