Time To Walk Away From Ad Hoc WIMPs/Axions/Whaterverons
Time to study nature again. The MACHO microlensing results have stood up for a decade and indicate that 100s of BILLIONS of ultracompact objects with a typical mass of about 0.5 solar mass populate our galaxy. That is 100s of billions, not 100 million. And that is a minimum estimate.
These objects cannot be baryonic or they would be visible at some wavelength of EM radiation. They cannot have formed in supernovae, or in the other conventional processes, since that would violate observed limits on the heavy metals content of the Galaxy.
The most logical and scientific interpretation of the MACHO and LIGO results is that galaxies are dominated by very large populations of black holes. Only primordial black holes would seem to pass the stringent criteria for what the MACHOs might be.
Magee and Hanna ( https://arxiv.org/pdf/1706.04947.pdf ) have shown this past summer that virtually ALL of the dark matter could be in the form of primordial black holes with a broad mass distribution in the stellar-mass range. This answer to the dark matter enigma was definitively predicted as far back as 1987 [ https://arxiv.org/abs/astro-ph/0002363 ], but was ignored in favor of no-show WIMPs.
It’s been 30 years of failure for subatomic particle dark matter. How long will it be before microlensing, FRB, and GW research efforts put a nail in the WIMP coffin and we can make some real progress in theoretical physics?