CMB Bounds on Primordial Black Holes via Radiation Capture
Abstract
We explore the capture of neutrinos and photons in the cosmic neutrino and photon background by primordial black holes (PBHs). We model this phenomenon as a gravitational interaction that effectively modifies the continuity equations for radiation and PBH densities and the cosmic expansion history. We find that the observability of this modified cosmic history is highly sensitive to PBH mass, and only extraordinarily massive PBHs would leave observable trace on the temperature and E-mode polarization of the cosmic microwave background (CMB). Specifically, Planck data restrict PBH abundance to fpbh≲ 10−1 for PBH masses above 1015 M⊙, getting considerably tighter for higher masses. We expect substantial improvement as high-resolution measurements of larger CMB multipoles become available. A future cosmic-variance-limited experiment, with ℓmax=7000, would set fpbh≲ 10−1−8× 10−5 (for the fiducial ΛCDM cosmology) across 1013−1018M⊙. These constraints would be comparable to the current limits at the high-mass end of the spectrum [Carr et al, 2026]. The gravitational interaction of PBHS with the cosmic background radiation and its imprints on CMB would thus provide an independent complementary probe of extraordinarily massive PBH abundance.
Versions
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BibTeX
@misc{farhang2026bounds,
title = {{CMB Bounds on Primordial Black Holes via Radiation Capture}},
author = {Marzieh Farhang and S. M. S. Movahed},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.05133},
eprint = {2606.05133},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.05133},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - CMB Bounds on Primordial Black Holes via Radiation Capture
AU - Marzieh Farhang
AU - S. M. S. Movahed
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2606.05133
UR - https://arxiv.org/abs/2606.05133
AB - We explore the capture of neutrinos and photons in the cosmic neutrino and photon background by primordial black holes (PBHs). We model this phenomenon as a gravitational interaction that effectively modifies the continuity equations for radiation and PBH densities and the cosmic expansion history. We find that the observability of this modified cosmic history is highly sensitive to PBH mass, and only extraordinarily massive PBHs would leave observable trace on the temperature and E-mode polarization of the cosmic microwave background (CMB). Specifically, Planck data restrict PBH abundance to f_pbh≲ 10^−1 for PBH masses above 10^15 M_⊙, getting considerably tighter for higher masses. We expect substantial improvement as high-resolution measurements of larger CMB multipoles become available. A future cosmic-variance-limited experiment, with ℓ_max=7000, would set f_pbh≲ 10^−1−8× 10^−5 (for the fiducial ΛCDM cosmology) across 10^13−10^18M_⊙. These constraints would be comparable to the current limits at the high-mass end of the spectrum [Carr et al, 2026]. The gravitational interaction of PBHS with the cosmic background radiation and its imprints on CMB would thus provide an independent complementary probe of extraordinarily massive PBH abundance.
ER -