Even if massive ( 10 M _ { \odot } \lesssim M \lesssim 10 ^ { 4 } M _ { \odot } ) primordial black holes ( PBHs ) can only account for a small fraction of the dark matter ( DM ) in the universe , they may still be responsible for a sizable fraction of the coalescence events measured by LIGO/Virgo , and/or act as progenitors of the supermassive black holes ( SMBHs ) observed already at high redshift ( z \gtrsim 6 ) .
In presence of a dominant , non-PBH DM component , the bounds set by CMB via an altered ionization history are modified .
We revisit the cosmological accretion of a DM halo around PBHs via toy models and dedicated numerical simulations , deriving updated CMB bounds which also take into account the last Planck data release .
We prove that these constraints dominate over other constraints available in the literature at masses M \gtrsim 20 - 50 M _ { \odot } ( depending on uncertainty in accretion physics ) , reaching the level f _ { PBH } < 3 \times 10 ^ { -9 } around M \sim 10 ^ { 4 } M _ { \odot } .
These tight bounds are nonetheless consistent with the hypothesis of a primordial origin of the SMBH massive seeds .