Searching for a subpopulation of primordial black holes in LIGO/Virgo
  gravitational-wave data
  With several dozen binary black hole events detected by LIGO/Virgo to date
and many more expected in the next few years, gravitational-wave astronomy is
shifting from individual-event analyses to population studies. Using the GWTC-2
catalog, we perform a hierarchical Bayesian analysis that for the first time
combines several state-of-the-art astrophysical formation models with a
population of primordial black holes (PBHs) and constrains the fraction of a
putative subpopulation of PBHs in the data. We find that this fraction depends
significantly on the set of assumed astrophysical models. While a primordial
population is statistically favored against certain competitive astrophysical
channels, such as globular clusters and nuclear stellar clusters, a dominant
contribution from the stable-mass-transfer isolated formation channel
drastically reduces the need for PBHs, except for explaining the rate of
mass-gap events like GW190521. The tantalizing possibility that black holes
formed after inflation are contributing to LIGO/Virgo observations could only
be verified by further reducing uncertainties in astrophysical and primordial
formation models, and it may ultimately be confirmed by third-generation
interferometers.
