Feedback in the dark: a critical examination of CMB bounds on primordial black holes
arxiv(2024)
摘要
If present in the early universe, primordial black holes (PBHs) will accrete
matter and emit high-energy photons, altering the statistical properties of the
Cosmic Microwave Background (CMB). This mechanism has been used to constrain
the fraction of dark matter that is in the form of PBHs to be much smaller than
unity for PBH masses well above one solar mass. Moreover, the presence of dense
dark matter mini-halos around the PBHs has been used to set even more stringent
constraints, as these would boost the accretion rates. In this work, we
critically revisit CMB constraints on PBHs taking into account the role of the
local ionization of the gas around them. We discuss how the local increase in
temperature around PBHs can prevent the dark matter mini-halos from strongly
enhancing the accretion process, in some cases significantly weakening
previously derived CMB constraints. We explore in detail the key ingredients of
the CMB bound and derive a conservative limit on the cosmological abundance of
massive PBHs.
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