Revisiting Primordial Black Holes Constraints from Ionization History

Abstract

Much attention has been drawn to the recent discoveries by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) of merging intermediate mass black holes. Of particular interest is the possibility that the merger events detected could be evidence of dark matter in the form of primordial black holes (PBHs). It has been argued that the presence of many black holes would effect the thermal and ionization history of the universe via their accretion of matter which would have strong signatures in the Cosmic Microwave Background's (CMB) power spectra evident in the damping of anisotropies and change in low-l polarization power. In general the accretion is quite sensitive to the specific physics involved and the conditions of the early universe. In this work, we take a minimal approach and find constraints on PBHs not including the model dependent effects of nonlinear structure of formation or transition between different accretion models which would work to increase the effect. In addition, we include the relative velocity between dark matter and baryonic matter including the effects of supersonic streaming at high redshift which work to significantly reduce the constraining power. We also examine the constraints on more astrophysically-motivated extended black hole mass functions and discuss how mergers might effect this distribution. We find constraints on PBHs in the range ≈ 30M , finding that they could not compose more than 10% of the total dark matter content.

Lower bound on the primordial black hole merger rate

“…Details of the calculation of these constraints and the fit are presented in [14]. The other constraints in this mass range arise from microlensing [31][32][33][34][35][36][37], dynamics of stars [38][39][40][41], and due to accreting PBHs affecting the CMB [42][43][44][45] or 21cm physics [23,46,47] .…”

Small-scale structure of primordial black hole dark matter and its implications for accretion

“…Recent revisions of the femtolensing [18] and the HSC/Subaru microlensing [19] surveys have opened the mass window 10 −16 −10 −11 M for PBH DM [20,21], that may be extended to even lower masses if their radiation would be modified [22]. For higher masses PBH abundance is constrained by microlensing [23][24][25][26], survival of stars in dwarf galaxies [27,28], survival of wide binaries [29], gravitational wave observations [7][8][9]30] and the modification of CMB [31][32][33][34] or 21cm physics [35,36] due to accreting PBHs.…”

Constant roll and primordial black holes

“…7 and 8, we focused on three different PBH mass scales, each of which corresponds to PBHs as LIGO-Virgo events (red), OGLE events (purple), and all dark matter (green), the first two of which could be possible 7. Diverse observational constraints are represented, including that on extra-galactic radiation (EGγ) [1], femto-lensing [39] long-livedness of white dwarfs (WD) [40], microlensing by the Subaru HSC [41], Kepler [42] and by EROS-2 and previous related searches [43], the survival of ultra-faint dwarf (UFD) galaxies [44], and the accretion on the CMB [45][46][47][48]. We also include the allowed parameter space assuming a detection by OGLE [6].…”