Primordial Black Holes from Vector-Induced Curvature Perturbations Sourced by Primordial Magnetic Fields

Abstract

Generating an appreciable abundance of primordial black holes (PBHs) requires a substantial enhancement of primordial curvature perturbations on small scales. In this Letter, we propose a new post-inflationary mechanism in which such an enhancement arises during a stiff, or kination, epoch. The mechanism is driven by metric vector perturbations sourced by the vector component of the electromagnetic stress-energy tensor associated with primordial magnetic fields (PMFs). Since these first-order vector modes remain approximately constant during kination, they act as persistent nonlinear sources for second-order scalar perturbations. We show that the resulting vector-induced curvature perturbations are amplified toward the infrared cutoff of the kination band and exhibit the characteristic scaling 𝒫_ℛ(k)∝ k⁻⁵. As a concrete realization, we consider PMFs generated in a Ratra-type magnetogenesis scenario and find that the induced curvature perturbations can produce PBHs with an abundance large enough to constitute a substantial fraction of the dark matter.

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BibTeX RIS

BibTeX

@misc{han2026primordial,
  title = {{Primordial Black Holes from Vector-Induced Curvature Perturbations Sourced by Primordial Magnetic Fields}},
  author = {Chang Han and Zu-Cheng Chen and Hongwei Yu and Puxun Wu},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2606.23307},
  eprint = {2606.23307},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2606.23307},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Primordial Black Holes from Vector-Induced Curvature Perturbations Sourced by Primordial Magnetic Fields
AU  - Chang Han
AU  - Zu-Cheng Chen
AU  - Hongwei Yu
AU  - Puxun Wu
PY  - 2026
DA  - 2026/11/04
PB  - arXiv
DO  - 10.48550/arxiv.2606.23307
UR  - https://arxiv.org/abs/2606.23307
AB  - Generating an appreciable abundance of primordial black holes (PBHs) requires a substantial enhancement of primordial curvature perturbations on small scales. In this Letter, we propose a new post-inflationary mechanism in which such an enhancement arises during a stiff, or kination, epoch. The mechanism is driven by metric vector perturbations sourced by the vector component of the electromagnetic stress-energy tensor associated with primordial magnetic fields (PMFs). Since these first-order vector modes remain approximately constant during kination, they act as persistent nonlinear sources for second-order scalar perturbations. We show that the resulting vector-induced curvature perturbations are amplified toward the infrared cutoff of the kination band and exhibit the characteristic scaling 𝒫_ℛ(k)∝ k^−5. As a concrete realization, we consider PMFs generated in a Ratra-type magnetogenesis scenario and find that the induced curvature perturbations can produce PBHs with an abundance large enough to constitute a substantial fraction of the dark matter.
ER  -

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