Axion constraints in non-standard thermal histories

Understand

It is usually assumed that dark matter is produced during the radiation dominated era.

• There is, however, no direct evidence for radiation domination prior to big-bang nucleosynthesis.
• Two non-standard thermal histories are considered.
• In one, the low-temperature-reheating scenario, radiation domination begins as late as 1 MeV, and is preceded by significant entropy generation.