From QFT to Boltzmann: Freeze-in in the presence of oscillating condensates

Understand

Scalar dark matter (DM), and axions in particular, have an irreducible abundance of particles produced by freeze-in due to portal interactions with the Standard Model plasma in the early Universe.

• In addition, vacuum misalignment and other mechanisms can lead to the presence of a cold, oscillating condensate.
• Therefore, generically, the evolution of the DM in both forms, condensate and particles, needs to be studied simultaneously.
• In non-equilibrium quantum field theory, the condensate and particles are described by one- and two-point functions, respectively.