Light scalar dark matter fields can exhibit several interesting aspects to their cosmological evolution. I will focus mostly on structure formation with ultralight axions and with the QCD axion. The standard scenario leads to a suppression of structure on small scales. I will show that there can also be an enhancement of power just below the scale of suppression. This effect will lead to the formation of compact axion halos, with broad implications for their observational prospects.
Cosmology reviews for:-- ultralight axions (Marsh): https://arxiv.org/abs/1510.07633
-- QCD axion (Wantz & Shellard): https://arxiv.org/abs/0910.1066
First mentions of the enhanced structure effect:
-- by Zhang & Chiueh https://arxiv.org/abs/1702.07065
-- by Cedeno et al https://arxiv.org/abs/1703.10180