Was there a negative vacuum energy in your past?

A new direction for dark matter research: intermediate-mass compact halo objects

“…The X-rays emitted by the accretion of this interstellar gas onto a DM population would heat the interstellar gas, which in turn would cause via the inverse Compton effect a distortion in the CMB both with regard to its spectrum and isotropy. A widely cited attempt to calculate this effect [23] employed the Bondi-Hoyle model for spherical accretion onto black holes, and carries through the computation all the way up to a point of comparison with limits on CMB spectral distortions derived from the COBE satellite observations. In particular it is claimed in [25] that the observed limits on the CMB distortion constrain the density of massive PBHs to only a tiny fraction < 10 −4 of the DM density.…”

“…Although it was initially thought that these PBHs would typically have masses much smaller than the mass of the Sun [8], theoretical arguments have been advanced [18][19][20] that PBHs with masses > 15M might have been prolifically produced at the onset of the big bang. Indeed there are cosmological models where primordial production of a DM density of either PBHs [21,22] or dark energy stars [23] with masses > 15M is favored. We will continue to use the acronym MACHO for these objects because for masses < 10 5 M such objects can contribute to the dark matter halo of our galaxy.…”