We examine the possibility that galactic halos are collisionless ensembles of scalar field “massive compact halo objects” (MACHOs). Using mass constraints from MACHO microlensing and from theoretical arguments on halos made up of massive black holes, as well as demanding also that scalar MACHO ensembles of all scales do not exhibit gravothermal instability (as required by consistency with observations of LSB galaxies), we obtain the range: $m\lesssim {10}^{-7}{M}_{\odot }$ or ${30M}_{\odot }\lesssim m\lesssim {100M}_{\odot }.$ The rather narrow mass range of large MACHOs seems to indicate that the ensembles we are suggesting should be probably made up of scalar MACHOs in the low mass range (“mini-MACHOs”). The proposed model allows one to consider a nonbaryonic and nonthermal fundamental nature of dark matter, while at the same time keeping the same phenomenology of the CDM paradigm.

• Received 11 February 2004

DOI:https://doi.org/10.1103/PhysRevD.70.043537