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We study the clustering of primordial black holes (PBHs) and axionminiclusters produced in the model proposed to explain the LIGO/Virgo events orthe seeds of the supermassive black holes (SMBHs) in arXiv:2006.13137. It isfound that this model predicts large isocurvature perturbations due to theclustering of PBHs and axion miniclusters, from which we obtain stringentconstraints on the model parameters. Specifically, for the axion decay constant$f_a=10^{16}~\mathrm{GeV}$, which potentially accounts for the seeds of theSMBHs, the PBH fraction in dark matter should be $f_\mathrm{PBH}\lesssim7\times10^{-10}$. Assuming that the mass of PBHs increases by more than a factor of$\mathcal{O}(10)$ due to accretion, this is consistent with the observedabundance of SMBHs. On the other hand, for $f_a=10^{17}~\mathrm{GeV}$ requiredto produce PBHs of masses detected in the LIGO/Virgo, the PBH fraction shouldbe $f_\mathrm{PBH}\lesssim6\times 10^{-8}$, which may be too small to explainthe LIGO/Virgo events, although there is a significant uncertainty incalculating the merger rate in the presence of clustering.

Clustering of Primordial Black Holes from QCD Axion Bubbles