Multiple ultralight axionic wave dark matter and astronomical structures

An ultralight scalar boson with mass m(1) similar or equal to 10(-22) eV is gaining credence as a Dark Matter (DM) candidate that explains the dark cores of dwarf galaxies as soliton waves. Such a boson is naturally interpreted as an axion generic in String Theory, with multiple light axions predicted in this context. We examine the possibility of soliton structures over a wide range of scales, accounting for galaxy core masses and the common presence of nuclear star clusters. We present a diagnostic soliton core mass-radius plot that provides a global view, indicating the existence of an additional axion with mass m(2) similar or equal to 10(-20) eV, with the possibility of a third axion with mass m(3) greater than or similar to 0.5 x 10(-18) eV. We also argue that the relative mass densities measured for these axions are consistent with their cosmological production via the mis-alignment mechanism. (C) 2020 Elsevier B.V. All rights reserved.