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arXiv · 2610.08175

Flavor decoherence and washout timing in nonthermal leptogenesis after inflation

Boliang Yu·Ruixin Zhou
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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, \(N_1\), 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.

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Boliang Yu, Ruixin Zhou. 2026-10-06. Flavor decoherence and washout timing in nonthermal leptogenesis after inflation. https://arxiv.org/abs/2610.08175

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