科研之友
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摘要
If axion-like particles (ALPs) constitute a major part of dark matter (DM), due to their bosonic nature and a relatively small mass, they could behave differently from the pointlike dark matter particles on the formation of the cosmic structures. When studying the structure formation, it is often useful to consider DM as a special fluid with a given density and a given velocity. ALP fluid obeys the same continuity equation compared to the pointlike collisionless DM, but has a different first-order velocity equation. In the linear regime of structure formation, the resulted observational differences are negligible for the QCD axions but can be interesting for very light ALPs.
