Primordial Black Hole Assisted Dirac Leptogenesis
Abstract
Dirac leptogenesis offers a qualitatively different route to the baryon asymmetry: total lepton number is conserved, but equal and opposite asymmetries are stored in the Standard Model and right handed neutrino sectors, with only the visible component processed by electroweak sphalerons. We present the first dedicated study of how evaporating primordial black holes (PBHs) modify this mechanism. In a minimal charged-scalar mediator setup, we solve the coupled Boltzmann system including thermal production, Hawking emission of the mediator X and of right handed neutrinos, the PBH contribution to the expansion rate, and entropy injection. We find that Hawking emission can populate X in regions where thermal production is inefficient, allowing its subsequent CP-violating decays to enhance the baryon asymmetry. For representative benchmarks, PBHs extend the successful region from mediator masses around 109 GeV down to about 106 GeV and can compensate for smaller effective CP asymmetries. This effect is not universal: where thermal Dirac leptogenesis is already efficient, PBHs can instead reduce the final asymmetry. Their evaporation also deposits energy in the right handed neutrino sector and contributes to ΔNeff. In the PBH parameter scan, part of the region that reproduces the observed baryon asymmetry lies below the Planck reference level ΔNeff=0.284 and above the projected CMB-S4 sensitivity ΔNeff=0.06.
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BibTeX
@misc{manno2026primordial,
title = {{Primordial Black Hole Assisted Dirac Leptogenesis}},
author = {Marco Manno and Anish Ghoshal},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.01717},
eprint = {2609.01717},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.01717},
}
RIS
TY - UNPB
TI - Primordial Black Hole Assisted Dirac Leptogenesis
AU - Marco Manno
AU - Anish Ghoshal
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.01717
UR - https://arxiv.org/abs/2609.01717
AB - Dirac leptogenesis offers a qualitatively different route to the baryon asymmetry: total lepton number is conserved, but equal and opposite asymmetries are stored in the Standard Model and right handed neutrino sectors, with only the visible component processed by electroweak sphalerons. We present the first dedicated study of how evaporating primordial black holes (PBHs) modify this mechanism. In a minimal charged-scalar mediator setup, we solve the coupled Boltzmann system including thermal production, Hawking emission of the mediator X and of right handed neutrinos, the PBH contribution to the expansion rate, and entropy injection. We find that Hawking emission can populate X in regions where thermal production is inefficient, allowing its subsequent CP-violating decays to enhance the baryon asymmetry. For representative benchmarks, PBHs extend the successful region from mediator masses around 10^9 GeV down to about 10^6 GeV and can compensate for smaller effective CP asymmetries. This effect is not universal: where thermal Dirac leptogenesis is already efficient, PBHs can instead reduce the final asymmetry. Their evaporation also deposits energy in the right handed neutrino sector and contributes to ΔN_eff. In the PBH parameter scan, part of the region that reproduces the observed baryon asymmetry lies below the Planck reference level ΔN_eff=0.284 and above the projected CMB-S4 sensitivity ΔN_eff=0.06.
ER -