Ultra-light dark matter

Ultra-light dark matter (ULDM) is a class of models (DM) where DM composed by bosons with masses ranging from $10^{-24}\, \mathrm{eV} < m \mathrm{eV}$. These have been receiving lot attention in the past few years given their interesting property forming Bose-Einstein condensate (BEC) or superfluid on galactic scales. BEC and superfluidity are one most striking quantum mechanical phenomena manifest macroscopic scales, upon condensation, particles behave as single coherent state, described wavefunction condensate. The idea that condensation takes place inside galaxies while outside behaves like normal cold particle DM. This wave nature scales arise can address some curiosities behaviour small maintaining successes LCDM large There many literature describe component condenses galaxies. In this review, we going to those classify them according different ways they achieve condensation. For that, review superfluidity, apply knowledge order explain construction phenomenology. We scale challenges these aim solve how ULDM alleviates them. present rich phenomenology astrophysical consequences. here cosmological tests used constrain models, together new future observations promise test regimes. finalize showing predictions consequence component, vortices interference, could represent smoking gun search alternative (Abridged)