CMB constraints on primordial black hole dark matter
  We revisit cosmic microwave background (CMB) constraints on primordial black
hole dark matter. Spectral distortion limits from COBE/FIRAS do not impose a
relevant constraint. Planck CMB anisotropy power spectra imply that primordial
black holes with $m_{BH}\gtrsim 5~M_{\odot}$ are disfavored. However, this is
susceptible to sizeable uncertainties due to the treatment of the black hole
accretion process. These constraints are weaker than those quoted in earlier
literature for the same observables.
