Collapse of an axion scalar field

The manuscript deals with an interacting scalar field that mimics the evolution of the so-called axion scalar dark matter or axion like particles with ultra-light masses. It is discussed that such a scalar along with an ordinary fluid description can collapse under strong gravity. The end state of the collapse depends on how the axion interacts with geometry and ordinary matter. For a self-interacting axion and an axion interacting with geometry the collapse may lead to a zero proper volume singularity or a bounce and total dispersal of the axion. However, for an axion interacting with the ordinary fluid description, there is no formation of singularity and the axion field exhibits periodic behavior before radiating away to zero value. Usually this collapse and dispersal is accompanied by a violation of the null energy condition for the ordinary fluid description.