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Leptogenesis with a GeV-Scale Quasi-Dirac Neutrino

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Stephen F. King, Soumen Kumar Manna, Rishav Roshan, Arunansu Sil

High Energy Physics - Phenomenology · Submitted 14 Oct 2026 · 89 references

Pith's verdict: Solid, well-motivated extension of their earlier model to the GeV scale; the central claim that Higgs-decay leptogenesis can produce the observed baryon asymmetry is supported by the analysis, though it relies on a few approximations taken from the literature.

T0 · AI review

How this review was made: An AI referee (deepseek/deepseek-v4-flash) read the paper on October 16, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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arXiv ID2610.20729 (version 1)
Pith IDGHF7X3NY, Pith's permanent record of this paper and its review
CitationArunansu Sil, Rishav Roshan, Soumen Kumar Manna, Stephen F. King. "Leptogenesis with a GeV-Scale Quasi-Dirac Neutrino." arXiv:2610.20729 (2026). https://pith.science/paper/GHF7X3NY
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The paper

The paper claims

Observed baryon asymmetry explained by GeV-scale quasi-Dirac neutrinos in Higgs decays.

The reading

This paper claims that the observed matter–antimatter asymmetry of the Universe can be generated by Higgs-boson decays into GeV-mass quasi-Dirac neutrinos—two nearly degenerate right-handed neutrinos that form a Dirac pair with a tiny mass splitting. The splitting arises naturally from a symmetry-breaking framework involving spontaneously broken global lepton number and a discrete Z2 symmetry, avoiding ad hoc assumptions. The mechanism works in the narrow temperature window between electroweak symmetry breaking and sphaleron freeze-out, using a CP asymmetry that is purely thermal in origin. The predicted active–sterile neutrino mixing falls within the reach of experiments like SHiP and FCC-ee, and the same symmetry-breaking sector produces gravitational waves from domain-wall annihilation, offering an independent test.

What carries the argument

The central objects are two quasi-degenerate right-handed neutrinos N1, N2 that constitute a quasi-Dirac fermion with mass MN ~ 0.1–10 GeV and a vacuum mass splitting ∆M0 = 2vφ²/Λ, where vφ is the vev of a scalar field that spontaneously breaks global U(1)L and Λ is the cutoff of dimension-five operators. The tiny ∆M0 is naturally generated by explicit symmetry-breaking operators and is essential for resonant enhancement of the CP asymmetry in the decay H → L N. Finite-temperature corrections add a thermal component ∆MT(x) to the splitting, and the total ∆M(x) = ∆M0 + ∆MT(x) governs the resonance condition. The CP asymmetry formula (Eq. 14) depends on the interplay of vacuum and thermal terms, while the decay width and thermal factor γ(x) ≈ 50 (for x ≪ 1) determine the efficiency. All parameters are connected to neutrino oscillation data via a specific parametrization of the Dirac mass matrix.

Extended reading notes

Core claim

The authors show that in a type-I seesaw model with spontaneously broken global lepton number (U(1)L) and a discrete Z2 symmetry, two right-handed neutrinos form an almost exact Dirac fermion with a tiny mass splitting generated by higher-dimensional operators. This quasi-Dirac neutrino, with mass 0.1–10 GeV, can produce the correct baryon asymmetry through out-of-equilibrium Higgs decays (H → L N) in the early Universe. The CP asymmetry arises solely from finite-temperature effects, because the required absorptive part in the loop diagram is absent at zero temperature. Successful leptogenesis occurs for vacuum mass splittings where the total splitting is dominated either by vacuum or thermal contributions, and the observed asymmetry can be reproduced for different Majorana phases. The viable parameter space for active–sterile mixing overlaps significantly with the projected sensitivities of SHiP, MATHUSLA, and FCC-ee.

Load-bearing premise

The model assumes equal coefficients c1 = c2 = 1 for the two dimension-five operators in Eq. (3), which enforces a CP symmetry under the transformation Φ → Φ*; any deviation would alter the mass splitting and introduce additional CP-violating phases, potentially invalidating the resonant enhancement and the predicted baryon asymmetry.

Editorial extensions

If this is right

  • If correct, the model predicts that heavy neutral leptons with masses 0.1–10 GeV and active–sterile mixing |θe|² in the range 10⁻⁹ to 10⁻⁷ should be detectable at SHiP, MATHUSLA, and FCC-ee.
  • The same symmetry-breaking sector that generates the neutrino mass splitting also produces domain walls that annihilate, emitting a stochastic gravitational-wave background detectable by LISA, ET, or DECIGO for suitable parameter choices.
  • The Majoron arising from U(1)L breaking cannot constitute stable dark matter in the parameter region of successful leptogenesis, but it can affect the effective number of relativistic species Neff, providing a distinct cosmological signature.
  • The Higgs-decay leptogenesis mechanism dominates over the ARS oscillation mechanism in the regime T_osc < T_sph, which corresponds to the smallest vacuum mass splittings, marking a clear parameter-space distinction.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The naturalness of the tiny mass splitting in this model suggests that successful leptogenesis could be tightly tied to the scale of global-symmetry breaking, potentially linking it to other beyond-Standard-Model phenomena such as axion physics or neutrino mass generation.
  • If future experiments like SHiP or FCC-ee observe a heavy neutral lepton in the predicted mass-mixing region, it would constitute strong evidence for the Higgs-decay leptogenesis scenario; a non-observation would push the required mass splitting to even smaller values, potentially requiring new physics to explain the degeneracy.
  • The model's connection to gravitational waves offers a unique multi-messenger probe: observing a stochastic GW background from domain walls at LISA would correlate with the baryogenesis mechanism, providing a cross-check independent of collider searches.
  • The tension between viable leptogenesis and Majoron dark matter hints that if a cosmologically stable Majoron were discovered, it would disfavor the parameter space where Higgs-decay leptogenesis alone explains the baryon asymmetry, possibly requiring additional ingredients.
Original abstract

We discuss leptogenesis in a model with a GeV-scale quasi-Dirac neutral lepton, comprising mainly sterile states, which is accessible to future experiments. In particular, we show that Higgs-decay leptogenesis can naturally arise from the type-I seesaw mechanism with spontaneously broken global lepton number together with a discrete $Z_2$ symmetry, yielding two quasi-degenerate right-handed neutrinos (RHNs) which, to excellent approximation, form a single Dirac neutrino, with a tiny mass splitting as required for resonant enhancement generated by higher-dimensional lepton-number-violating operators. Incorporating finite-temperature effects, we show that the observed baryon asymmetry can be successfully generated through thermal Higgs decays for 0.1-10 GeV mass quasi-Dirac neutrinos, with the CP asymmetry arising from the interplay between the vacuum and thermal contributions to the mass splitting. In the parameter region of successful leptogenesis, the quasi-Dirac neutrino is accessible to future heavy neutral lepton searches at SHiP, MATHUSLA and FCC-ee. In addition, the same symmetry-breaking sector gives rise to unstable domain walls whose annihilation can generate a stochastic gravitational-wave background, providing a complementary probe of the framework.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-10-16: 1 request, 4,575 input tokens.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.14 · human participants 0.01 · controlled comparison 0.02 · randomized assignment 0.01 · states quantitative result 0.78 · compares with prior results 0.08 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

We discuss leptogenesis in a model with a GeV-scale quasi-Dirac neutral lepton, comprising mainly sterile states, which is accessible to future experiments. In particular, we show that Higgs-decay leptogenesis can naturally arise from the type-I seesaw mechanism with spontaneously broken global lepton number together with a discrete $Z_2$ symmetry, yielding two quasi-degenerate right-handed neutrinos (RHNs) which, to excellent approximation, form a single Dirac neutrino, with a tiny mass splitting as required for resonant enhancement generated by higher-dimensional lepton-number-violating operators. Incorporating finite-temperature effects, we show that the observed baryon asymmetry can be successfully generated through thermal Higgs decays for 0.1-10 GeV mass quasi-Dirac neutrinos, with the CP asymmetry arising from the interplay between the vacuum and thermal contributions to the mass splitting. In the parameter region of successful leptogenesis, the quasi-Dirac neutrino is accessible to future heavy neutral lepton searches at SHiP, MATHUSLA and FCC-ee. In addition, the same symmetry-breaking sector gives rise to unstable domain walls whose annihilation can generate a stochastic gravitational-wave background, providing a complementary probe of the framework.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We discuss leptogenesis in a model with a GeV-scale quasi-Dirac neutral lepton, comprising mainly sterile states, which is accessible to future experiments. contribution 0.98 0.52 0.25 asserted 0.77
s1 In particular, we show that Higgs-decay leptogenesis can naturally arise from the type-I seesaw mechanism with spontaneously broken global lepton number together with a discrete $Z_2$ symmetry, yielding two quasi-degenerate right-handed neutrinos (RHNs) which, to excellent approximation, form a single Dirac neutrino, with a tiny mass splitting as required for resonant enhancement generated by higher-dimensional lepton-number-violating operators. contribution 0.67 0.85 0.22 asserted 1.00
s2 Incorporating finite-temperature effects, we show that the observed baryon asymmetry can be successfully generated through thermal Higgs decays for 0.1-10 GeV mass quasi-Dirac neutrinos, with the CP asymmetry arising from the interplay between the vacuum and thermal contributions to the mass splitting. result 0.94 0.92 0.39 asserted 1.00
s3 In the parameter region of successful leptogenesis, the quasi-Dirac neutrino is accessible to future heavy neutral lepton searches at SHiP, MATHUSLA and FCC-ee. result 0.52 0.77 0.21 asserted 0.94
s4 In addition, the same symmetry-breaking sector gives rise to unstable domain walls whose annihilation can generate a stochastic gravitational-wave background, providing a complementary probe of the framework. result 0.64 0.75 0.09 asserted 0.70

What kind of paper the classifier reports this is: theoretical result 1.00 · evidence from proof or derivation 0.82.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. FIG. 1. Tree-level and self-energy diagrams contributing to
Figure 2. FIG. 2. Region of parameter space in the ∆
Figure 3. FIG. 3. Evolution of the
Figure 5. FIG. 5. Baryon asymmetry (
Figure 6. FIG. 6. Baryon asymmetry (
Figure 7. FIG. 7. Present (shaded region) and projected (coloured contours) bounds on the active-sterile mixing parameter
Figure 8. FIG. 8. Viable regions in the
Figure 9. FIG. 9. The GW spectrum produced from the annihilation
Figure 10. FIG. 10. The GW spectrum produced from the annihilation

Showing 9 of the paper's 10 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:2610.20729 by the authors.

References

Discussion

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