Matter-Antimatter Asymmetry from Dirac-Majorana Flip-Flop
Abstract
The observed matter-antimatter asymmetry can be generated dynamically via leptogenesis, where a non-zero lepton asymmetry is generated first and then gets converted into baryon asymmetry via sphalerons. Creation of non-zero lepton asymmetry typically requires lepton number violation (LNV) which, within the seesaw framework, results in the Majorana nature of light neutrinos. With no signs of LNV at terrestrial experiments, we propose a novel leptogenesis scenario where LNV occurs at high temperatures while zero-temperature physics is consistent with the pure Dirac nature of neutrinos. In a concrete model of this "Dirac-Majorana flip-flop", the right chiral parts of Dirac neutrinos initially acquire a large Majorana mass in the early Universe when a singlet scalar field with two units of lepton number acquires a non-zero vacuum expectation value (VEV), thereby facilitating leptogenesis from out-of-equilibrium decay of heavy Majorana fermions. At lower temperatures, the VEV of the scalar singlet gets restored to zero to be consistent with lepton number conservation. A first-order VEV-restoring phase transition can lead to observable gravitational waves, while light Dirac neutrinos can generate detectable dark radiation at cosmic microwave background experiments.
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BibTeX
@misc{borah2026matterantimatter,
title = {{Matter-Antimatter Asymmetry from Dirac-Majorana Flip-Flop}},
author = {Debasish Borah and Arnab Dasgupta and Debalina Nandy and Indrajit Saha and Harman Singh},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.10688},
eprint = {2610.10688},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.10688},
}
RIS
TY - UNPB
TI - Matter-Antimatter Asymmetry from Dirac-Majorana Flip-Flop
AU - Debasish Borah
AU - Arnab Dasgupta
AU - Debalina Nandy
AU - Indrajit Saha
AU - Harman Singh
PY - 2026
DA - 2026/10/07
PB - arXiv
DO - 10.48550/arxiv.2610.10688
UR - https://arxiv.org/abs/2610.10688
AB - The observed matter-antimatter asymmetry can be generated dynamically via leptogenesis, where a non-zero lepton asymmetry is generated first and then gets converted into baryon asymmetry via sphalerons. Creation of non-zero lepton asymmetry typically requires lepton number violation (LNV) which, within the seesaw framework, results in the Majorana nature of light neutrinos. With no signs of LNV at terrestrial experiments, we propose a novel leptogenesis scenario where LNV occurs at high temperatures while zero-temperature physics is consistent with the pure Dirac nature of neutrinos. In a concrete model of this "Dirac-Majorana flip-flop", the right chiral parts of Dirac neutrinos initially acquire a large Majorana mass in the early Universe when a singlet scalar field with two units of lepton number acquires a non-zero vacuum expectation value (VEV), thereby facilitating leptogenesis from out-of-equilibrium decay of heavy Majorana fermions. At lower temperatures, the VEV of the scalar singlet gets restored to zero to be consistent with lepton number conservation. A first-order VEV-restoring phase transition can lead to observable gravitational waves, while light Dirac neutrinos can generate detectable dark radiation at cosmic microwave background experiments.
ER -