The merger history of primordial-black-hole binaries
  As a candidate of dark matter, primordial black holes (PBHs) have attracted
more and more attentions as they could be possible progenitors of the heavy
binary black holes (BBHs) observed by LIGO/Virgo. Accurately estimating the
merger rate of PBH binaries will be crucial to reconstruct the mass
distribution of PBHs. It was pointed out the merger history of PBHs may shift
the merger rate distribution depending on the mass function of PBHs. In this
paper, we use 10 BBH events from LIGO/Virgo O1 and O2 observing runs to
constrain the merger rate distribution of PBHs by accounting the effect of
merger history. It is found that the second merger process makes subdominant
contribution to the total merger rate, and hence the merger history effect can
be safely neglected.
