Flavor decoherence and washout timing in nonthermal leptogenesis after inflation
Abstract
We investigate why changing the heavy-neutrino mass hierarchy can reverse the baryon asymmetry in nonthermal leptogenesis after hilltop inflation. Along the mass trajectory studied here, lowering the mass of the lighter state, N1, reverses the final asymmetry while leaving the dominant injection from N2 decays nearly unchanged. The mass change primarily delays N1 washout relative to electron--muon flavor decoherence; at fixed source and background, translating the washout history while preserving its shape and integrated strength reproduces more than 99\% of the yield changes from the nonthermal N2 source at two physical target masses. Decomposing the N2 CP source shows that the projector-aligned component remains positive under both washout histories, whereas the initially trace-free component reverses its propagated contribution and accounts for about 99.7\% of the timing contrast in the fixed-source comparison. Rapid damping of eμ flavor coherence largely removes this contrast, while rapid chemical equilibration does not. Later washout therefore acts on a more decohered flavor state, reducing the positive eμ contribution and allowing negative diagonal contributions to determine the final sign. At a mass recomputed to reproduce the observed baryon yield, a 10\% increase of the muon collision operator reverses the sign in a fixed-input sensitivity test.
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BibTeX
@misc{yu2026flavor,
title = {{Flavor decoherence and washout timing in nonthermal leptogenesis after inflation}},
author = {Boliang Yu and Ruixin Zhou},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.08175},
eprint = {2610.08175},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.08175},
}
RIS
TY - UNPB
TI - Flavor decoherence and washout timing in nonthermal leptogenesis after inflation
AU - Boliang Yu
AU - Ruixin Zhou
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2610.08175
UR - https://arxiv.org/abs/2610.08175
AB - We investigate why changing the heavy-neutrino mass hierarchy can reverse the baryon asymmetry in nonthermal leptogenesis after hilltop inflation. Along the mass trajectory studied here, lowering the mass of the lighter state, N_1, reverses the final asymmetry while leaving the dominant injection from N_2 decays nearly unchanged. The mass change primarily delays N_1 washout relative to electron--muon flavor decoherence; at fixed source and background, translating the washout history while preserving its shape and integrated strength reproduces more than 99\% of the yield changes from the nonthermal N_2 source at two physical target masses. Decomposing the N_2 CP source shows that the projector-aligned component remains positive under both washout histories, whereas the initially trace-free component reverses its propagated contribution and accounts for about 99.7\% of the timing contrast in the fixed-source comparison. Rapid damping of eμ flavor coherence largely removes this contrast, while rapid chemical equilibration does not. Later washout therefore acts on a more decohered flavor state, reducing the positive eμ contribution and allowing negative diagonal contributions to determine the final sign. At a mass recomputed to reproduce the observed baryon yield, a 10\% increase of the muon collision operator reverses the sign in a fixed-input sensitivity test.
ER -