The Axion Universe

Abstract

The standard models of cosmology and particle physics have met enormous success. However,there are still a few big questions that remain to be answered. One of these outstanding questions is “what is the dark matter?”. One of the most well-motivated dark matter candidates is the axion, as it provides a natural solution to another fundamental problem called the strong CP problem. Axions can also be motivated by various theories in high energy physics. A Universe with axion dark matter is very colorful as one expects many planetary-mass collapsed structures and potentially compact clumps such as axion stars. Astrophysical and cosmological observations can be sensitive to these structures, providing a unique window into the nature of dark matter. We will discuss recent progress in the evolution, formation, and detectable signals of axion minihalos and axion stars.