New opportunities for axion dark matter searches in nonstandard cosmological models

Understand

We study axion dark matter production from a misalignment mechanism in scenarios featuring a general nonstandard cosmology.

• Before the onset of Big Bang nucleosynthesis, the energy density of the universe is dominated by a particle field $\phi$ described by a general equation of state $\omega$.
• The ensuing enhancement of the Hubble expansion rate decreases the temperature at which axions start to oscillate, opening this way the possibility for axions heavier than in the standard window.
• This is the case for kination, or in general for scenarios with $\omega > 1/3$.