Coherent vs. Squeezed Fluctuations of Ultralight Dark Matter

Ultralight dark matter candidates with masses below 1 eV are often considered to behave "classically". By this, one typically means that the dark matter exists in a coherent state (of the harmonic oscillator defined by the creation/annihilation operators of its momentum modes). This would, for instance, be the case for virialized dark matter, which might be observed in a laboratory experiment. On cosmological scales, however, if dark matter exhibits isocurvature fluctuations which were produced by inflation, these fluctuations will instead exist in a squeezed state. In this chalk talk, I will describe these two possible states of dark matter and show that they can be distinguished solely by observing the statistics of its density fluctuations. If time allows, I will also discuss the cosmological dynamics of this squeezed state and the parameter space in which it may survive until today.