ALP dark matter from kinetic fragmentation: opening up the parameter window

The main mechanism responsible for Axion-Like-Particle (ALP) production in the early universe is so-called misalignment mechanism. Three regimes have been investigated this context: standard misalignment, large and kinetic misalignment. latter applies if axion inherits a initial velocity universe, such that field rolls through many wiggles during its evolution, before it gets trapped one minimum. This largely opens region of parameter space ALP dark matter towards higher values axion-photon coupling, which can be probed by whole set next decade's upcoming experiments. In fact, almost entire [mass, decay constant] plane now accommodate matter. paper, we show always entirely fragmented, meaning energy density homogeneous redistributed over higher-mode axions. We present general model-independent analytical description fragmentation, including discussion modified conditions mode functions due to axion's velocity, how they impact growth adiabatic fluctuations. calculate precisely regions corresponding respectively with weak fragmentation after trapping trapping. While precise determination relic abundance, another observational implication formation much denser compact halos, described companion paper. also point out new gravitational-wave signature arises regime complete could seen measurements $\mu$ distortions Cosmic Microwave Background.