Near-Resonant Thermal Leptogenesis
Pith reviewed 2026-05-16 07:00 UTC · model grok-4.3
The pith
Quasi-degenerate right-handed neutrinos produce the baryon asymmetry down to electroweak scales without resonance.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In the quasi-degenerate but non-resonant regime, the CP asymmetry parameter is expanded near mass degeneracy subject to the condition ΔM > 100Γ_i, which produces the bound ε ≤ 1/200 independent of effective neutrino masses and right-handed neutrino mass. This enables successful baryon asymmetry generation by right-handed neutrino decays for M ≳ 100 GeV independent of washout regime, and during reheating down to T_RH ≃ 10 GeV, with a consistent treatment of flavour effects.
What carries the argument
The CP asymmetry parameter ε expanded near degeneracy under the non-resonance condition ΔM > 100Γ_i, which supplies the universal bound and controls the viable parameter space.
If this is right
- Successful leptogenesis occurs for right-handed neutrino masses M ≳ 100 GeV independent of washout regime.
- Baryon asymmetry generation remains possible with reheating temperatures as low as 10 GeV without non-thermal production.
- Flavour effects can be incorporated consistently into near-resonant leptogenesis during reheating.
- The leptogenesis scale reaches the electroweak range without invoking resonance.
Where Pith is reading between the lines
- This regime could be probed by collider searches for right-handed neutrinos with small but non-resonant mass splittings.
- It supplies an alternative path for low-scale seesaw models to accommodate the observed asymmetry without high reheating temperatures.
- Extensions could test how specific flavour structures modify the 1/200 bound in concrete neutrino mass models.
Load-bearing premise
The factor of 100 in the imposed condition ΔM > 100Γ_i is sufficient to justify the perturbative expansion near degeneracy while still permitting enough asymmetry for successful leptogenesis.
What would settle it
A full calculation of the CP asymmetry for mass splittings satisfying 10Γ_i < ΔM < 100Γ_i that yields values larger than 1/200 would show the derived bound does not hold.
Figures
read the original abstract
We study leptogenesis in the quasi-degenerate but non-resonant regime. Expanding the CP asymmetry parameter near degeneracy and imposing the conservative non-resonance condition that the mass splitting must be much greater than the right-handed neutrino decay rates $\Delta M > 100\Gamma_i$, yields the universal upper bound $\epsilon \leq 1/200$, independent of both the effective neutrino masses and the right-handed neutrino mass. We investigate vanilla and flavoured near-resonant leptogenesis and find that successful leptogenesis by right-handed neutrino decays can occur for $M \gtrsim 100~\mathrm{GeV}$ independent of washout regime, extending the viable parameter space of thermal leptogenesis down to the electroweak scale without invoking resonance. We also analyse near-resonant thermal leptogenesis during reheating and show that successful baryon asymmetry generation is compatible with reheating temperatures as low as $T_{RH}\simeq 10\rm GeV$ without relying on non-thermal production. Finally, we present a consistent framework for incorporating flavour effects in near-resonant leptogenesis during reheating. Overall, near-resonant thermal leptogenesis offers a controlled alternative regime to resonant leptogenesis, lowering the leptogenesis scale to the electroweak scale, without reliance on a disputed regulator used in resonant leptogenesis.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies thermal leptogenesis in the quasi-degenerate but non-resonant regime. Expanding the CP asymmetry near degeneracy and imposing the condition ΔM > 100Γ_i yields a claimed universal upper bound ε ≤ 1/200 independent of effective neutrino masses and right-handed neutrino mass. It argues that successful leptogenesis remains possible for M ≳ 100 GeV and during reheating with T_RH ≃ 10 GeV, offering a controlled alternative to resonant leptogenesis without disputed regulators.
Significance. If the bound and regime validity hold, the work meaningfully extends the viable parameter space of thermal leptogenesis to the electroweak scale in a perturbative manner. The universal bound and low-scale reheating compatibility could inform model building for baryogenesis, while the flavour analysis during reheating adds a useful technical framework.
major comments (1)
- [expansion near degeneracy and imposition of ΔM > 100Γ_i] The derivation of the universal bound ε ≤ 1/200 (abstract) relies on imposing the specific non-resonance cutoff ΔM > 100Γ_i to truncate the near-degeneracy expansion. This factor directly sets the numerical value of the bound, yet the manuscript provides no explicit demonstration that higher-order terms remain negligible at Γ/ΔM ≈ 0.01 or that mass-dependent corrections do not re-enter; altering the cutoff factor would proportionally rescale ε_max, making the choice load-bearing rather than derived.
minor comments (2)
- [Abstract] The abstract states independence from effective neutrino masses and M; cross-reference the explicit equation or step in the expansion where this independence is proven.
- [near-resonant thermal leptogenesis during reheating] In the reheating section, clarify the precise relation between T_RH, the decay rates Γ_i, and the imposed cutoff to ensure the perturbative regime remains consistent at low temperatures.
Simulated Author's Rebuttal
We thank the referee for their careful reading of our manuscript and for the positive assessment of its potential significance in extending the viable parameter space of thermal leptogenesis. We address the major comment below and agree that the justification of our non-resonance cutoff requires strengthening. We will revise the manuscript accordingly.
read point-by-point responses
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Referee: The derivation of the universal bound ε ≤ 1/200 (abstract) relies on imposing the specific non-resonance cutoff ΔM > 100Γ_i to truncate the near-degeneracy expansion. This factor directly sets the numerical value of the bound, yet the manuscript provides no explicit demonstration that higher-order terms remain negligible at Γ/ΔM ≈ 0.01 or that mass-dependent corrections do not re-enter; altering the cutoff factor would proportionally rescale ε_max, making the choice load-bearing rather than derived.
Authors: We appreciate this observation. The factor of 100 in ΔM > 100Γ_i was chosen as a conservative threshold to ensure the system remains firmly in the non-resonant regime, where the leading term in the near-degeneracy expansion of the CP asymmetry dominates and higher-order contributions in powers of Γ/ΔM are strongly suppressed. At Γ/ΔM = 0.01 the next-to-leading corrections scale as (Γ/ΔM)^2 ≈ 10^{-4} and are negligible for the purposes of deriving the bound. We acknowledge, however, that the original manuscript did not contain an explicit demonstration of this suppression or an assessment of possible mass-dependent corrections. In the revised version we will add a dedicated paragraph (or short appendix) that estimates the truncation error of the expansion, compares the leading-order result to the exact expression in a benchmark case, and confirms that mass-dependent terms remain subdominant throughout the parameter region of interest. This addition will substantiate the cutoff without altering the numerical value of the bound or the main conclusions. revision: yes
Circularity Check
Universal bound ε ≤ 1/200 is constructed by imposing ΔM > 100Γ_i on the near-degeneracy expansion
specific steps
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fitted input called prediction
[Abstract]
"imposing the conservative non-resonance condition that the mass splitting must be much greater than the right-handed neutrino decay rates ΔM > 100Γ_i, yields the universal upper bound ε ≤ 1/200, independent of both the effective neutrino masses and the right-handed neutrino mass."
The bound ε ≤ 1/200 is obtained by substituting the imposed cutoff ΔM = 100Γ_i into the expanded expression for the CP asymmetry. Because the asymmetry scales proportionally with Γ/ΔM in the near-degenerate expansion, the specific numerical limit is forced by the arbitrary choice of the factor 100; changing the threshold to 10 or 1000 would proportionally rescale the bound, making the result equivalent to the input condition by construction.
full rationale
The paper expands the CP asymmetry near degeneracy and then imposes the condition ΔM > 100Γ_i to obtain the bound ε ≤ 1/200. This numerical value is the direct output of evaluating the expansion at the chosen cutoff (where the expansion parameter Γ/ΔM = 0.01), so the claimed universal upper bound reduces to the modeling choice of the factor 100 rather than an independent first-principles result. The derivation chain is self-contained in the expansion plus the externally imposed threshold, with no load-bearing self-citations or other circular patterns identified from the provided text.
Axiom & Free-Parameter Ledger
free parameters (1)
- non-resonance cutoff factor
axioms (2)
- domain assumption Standard Boltzmann equations govern the evolution of lepton asymmetry in the early universe
- ad hoc to paper The perturbative expansion near degeneracy remains valid when ΔM > 100Γ_i
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Expanding the CP asymmetry parameter near degeneracy ... ΔM >100Γ_i, yields the universal upper bound ε≤1/200
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
ϵi ≃ 1/16π (Mi/ΔM) Im[(y†y)²ij]/(y†y)ii ≤ 1/16π (Mi/ΔM)(y†y)jj
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Forward citations
Cited by 1 Pith paper
-
Linking Leptogenesis and Asymmetric Dark Matter: A Testable Framework for Neutrino Mass and the Matter-Antimatter Asymmetry
A leptogenesis framework generates both baryon asymmetry and asymmetric dark matter via heavy Majorana neutrino decays, enabling a TeV-scale seesaw with hierarchical couplings and testable spin-independent DM cross se...
Reference graph
Works this paper leans on
-
[1]
Bound on Reheating Temperature 22 C
Rescaling Variables 19 B. Bound on Reheating Temperature 22 C. Flavour Effects 25 V. Conclusions26 Acknowledgements27 References27 I. INTRODUCTION The observation of neutrino oscillations [1–9] confirmed that neutrinos have non-zero masses. This is inconsistent with the Standard Model, in which neutrinos are exactly mass- less, and therefore requires an e...
-
[2]
In the limitsM i ≫m D the seesaw relation is achieved. We adopt the Casas–Ibarra parametrisation of the Yukawa matrix, which allows us to express the neutrino Yukawa couplings in terms of low-energy neutrino data, heavy neutrino masses, the PMNS matrix, and a complex orthogonal matrix. Y= 1 v U √mν RT √ M .(2) A key quantity derived from this matrix, whic...
-
[3]
Rescaling Variables To make the Boltzmann equations numerically tractable it is convenient to introduce comoving variables that absorb the dilution factors due to the cosmic expansion. We define our parameters in terms of the scale factor a Eϕ ≡ρ ϕa3, E N ≡ρ N a3, E R ≡ρ Ra4, N B−L ≡n B−La3, x≡lna,(37) 19 The new variablex= lnais the number of e-folds act...
-
[4]
S. Fukuda et al. Constraints on neutrino oscillations using 1258 days of super-kamiokande solar neutrino data.Physical Review Letters, 86(25):5656–5660, June 2001
work page 2001
-
[5]
S. Fukuda et al. Determination of solar neutrino oscillation parameters using 1496 days of super-kamiokande-i data.Physics Letters B, 539(3–4):179–187, July 2002
work page 2002
-
[6]
Q. R. Ahmad et al. Direct evidence for neutrino flavor transformation from neutral-current interactions in the sudbury neutrino observatory.Physical Review Letters, 89(1), June 2002
work page 2002
-
[7]
Y. Ashie et al. Measurement of atmospheric neutrino oscillation parameters by super- kamiokande i.Physical Review D, 71(11), June 2005
work page 2005
- [8]
- [9]
- [10]
-
[11]
O. Yu. Smirnov et al. Measurement of neutrino flux from the primary proton–proton fusion process in the sun with borexino detector.Physics of Particles and Nuclei, 47(6):995–1002, November 2016
work page 2016
-
[12]
M.G. Aartsen et al. Measurement of atmospheric neutrino oscillations at 6–56gev with icecube deepcore.Physical Review Letters, 120(7), February 2018
work page 2018
-
[13]
Peter Minkowski.µ→eγat a Rate of One Out of 1-Billion Muon Decays?Phys. Lett. B, 67:421–428, 1977
work page 1977
-
[14]
Complex Spinors and Unified Theories.Conf
Murray Gell-Mann, Pierre Ramond, and Richard Slansky. Complex Spinors and Unified Theories.Conf. Proc. C, 790927:315–321, 1979
work page 1979
-
[15]
Horizontal gauge symmetry and masses of neutrinos.Conf
Tsutomu Yanagida. Horizontal gauge symmetry and masses of neutrinos.Conf. Proc. C, 7902131:95–99, 1979
work page 1979
-
[16]
Mohapatra and Goran Senjanovic
Rabindra N. Mohapatra and Goran Senjanovic. Neutrino Masses and Mixings in Gauge Models with Spontaneous Parity Violation.Phys. Rev. D, 23:165, 1981
work page 1981
-
[17]
M. Fukugita and T. Yanagida. Baryogenesis Without Grand Unification.Phys. Lett. B, 174:45–47, 1986
work page 1986
-
[18]
Markus A. Luty. Baryogenesis via leptogenesis.Phys. Rev. D, 45:455–465, 1992
work page 1992
-
[19]
G.F. Giudice, A. Notari, M. Raidal, A. Riotto, and A. Strumia. Towards a complete theory of thermal leptogenesis in the sm and mssm.Nuclear Physics B, 685(1–3):89–149, May 2004
work page 2004
-
[20]
Cp violating decays in leptogenesis scenarios.Physics Letters B, 384(1–4):169–174, September 1996
Laura Covi, Esteban Roulet, and Francesco Vissani. Cp violating decays in leptogenesis scenarios.Physics Letters B, 384(1–4):169–174, September 1996
work page 1996
-
[21]
W. Buchm¨ uller, P. Di Bari, and M. Pl¨ umacher. Leptogenesis for pedestrians.Annals of Physics, 315(2):305–351, February 2005
work page 2005
-
[22]
A. D. Sakharov. Violation of CP Invariance, C asymmetry, and baryon asymmetry of the universe.Pisma Zh. Eksp. Teor. Fiz., 5:32–35, 1967
work page 1967
-
[23]
Edward W. Kolb and Stephen Wolfram. Baryon Number Generation in the Early Universe. Nucl. Phys. B, 172:224, 1980. [Erratum: Nucl.Phys.B 195, 542 (1982)]
work page 1980
-
[24]
S. Yu. Khlebnikov and M. E. Shaposhnikov. The Statistical Theory of Anomalous Fermion Number Nonconservation.Nucl. Phys. B, 308:885–912, 1988. 28
work page 1988
-
[25]
Apostolos Pilaftsis. Cp violation and baryogenesis due to heavy majorana neutrinos.Physical Review D, 56(9):5431–5451, November 1997
work page 1997
-
[26]
A. Anisimov, A. Broncano, and M. Pl¨ umacher. The cp-asymmetry in resonant leptogenesis. Nuclear Physics B, 737(1–2):176–189, March 2006
work page 2006
-
[27]
Bj¨ orn Garbrecht, Florian Gautier, and Juraj Klaric. Strong washout approximation to reso- nant leptogenesis.Journal of Cosmology and Astroparticle Physics, 2014(09):033–033, Septem- ber 2014
work page 2014
-
[28]
Leptogenesis from first principles in the resonant regime.Annals of Physics, 328:26–63, January 2013
Mathias Garny, Alexander Kartavtsev, and Andreas Hohenegger. Leptogenesis from first principles in the resonant regime.Annals of Physics, 328:26–63, January 2013
work page 2013
-
[29]
Andrea De Simone and Antonio Riotto. On resonant leptogenesis.Journal of Cosmology and Astroparticle Physics, 2007(08):013–013, August 2007
work page 2007
-
[30]
Juraj Klaric, Mikhail Shaposhnikov, and Inar Timiryasov. Reconciling resonant leptogenesis and baryogenesis via neutrino oscillations.Physical Review D, 104(5), September 2021
work page 2021
-
[31]
Alan H. Guth. The Inflationary Universe: A Possible Solution to the Horizon and Flatness Problems.Phys. Rev. D, 23:347–356, 1981
work page 1981
-
[32]
Andrei D. Linde. A New Inflationary Universe Scenario: A Possible Solution of the Horizon, Flatness, Homogeneity, Isotropy and Primordial Monopole Problems.Phys. Lett. B, 108:389– 393, 1982
work page 1982
-
[33]
David H. Lyth and Antonio Riotto. Particle physics models of inflation and the cosmological density perturbation.Phys. Rept., 314:1–146, 1999
work page 1999
-
[34]
F. Hahn-Woernle and M. Pl¨ umacher. Effects of reheating on leptogenesis.Nuclear Physics B, 806(1–2):68–83, January 2009
work page 2009
-
[35]
Flavor leptogenesis during reheating era, 2023
Arghyajit Datta, Rishav Roshan, and Arunansu Sil. Flavor leptogenesis during reheating era, 2023
work page 2023
-
[36]
Effects of reheating on charged lepton yukawa equilibration and leptogenesis, 2024
Arghyajit Datta, Rishav Roshan, and Arunansu Sil. Effects of reheating on charged lepton yukawa equilibration and leptogenesis, 2024
work page 2024
-
[37]
Towards a systematic study of non-thermal leptogenesis from inflaton decays, 2024
Xinyi Zhang. Towards a systematic study of non-thermal leptogenesis from inflaton decays, 2024
work page 2024
-
[38]
Enrico Nardi, Yosef Nir, Juan Racker, and Esteban Roulet. On higgs and sphaleron effects during the leptogenesis era.Journal of High Energy Physics, 2006(01):068–068, January 2006
work page 2006
-
[39]
The Importance of flavor in 29 leptogenesis.JHEP, 01:164, 2006
Enrico Nardi, Yosef Nir, Esteban Roulet, and Juan Racker. The Importance of flavor in 29 leptogenesis.JHEP, 01:164, 2006
work page 2006
-
[40]
Asmaa Abada, Sacha Davidson, Francois-Xavier Josse-Michaux, Marta Losada, and Anto- nio Riotto. Flavour issues in leptogenesis.Journal of Cosmology and Astroparticle Physics, 2006(04):004–004, April 2006
work page 2006
-
[41]
S Antusch, S F King, and A Riotto. Flavour-dependent leptogenesis with sequential domi- nance.Journal of Cosmology and Astroparticle Physics, 2006(11):011–011, November 2006
work page 2006
-
[42]
Steve Blanchet and Pasquale Di Bari. Flavour effects on leptogenesis predictions.Journal of Cosmology and Astroparticle Physics, 2007(03):018–018, March 2007
work page 2007
-
[43]
On the impact of flavour oscillations in leptogenesis
Andrea De Simone and Antonio Riotto. On the impact of flavour oscillations in leptogenesis. JCAP, 02:005, 2007
work page 2007
-
[44]
Vincenzo Cirigliano, Christopher Lee, Michael J. Ramsey-Musolf, and Sean Tulin. Flavored quantum boltzmann equations.Physical Review D, 81(10), May 2010
work page 2010
-
[45]
Quantum boltzmann equations and leptogenesis
Andrea De Simone and Antonio Riotto. Quantum boltzmann equations and leptogenesis. Journal of Cosmology and Astroparticle Physics, 2007(08):002–002, August 2007
work page 2007
-
[46]
J Racker, Manuel Pe˜ na, and Nuria Rius. Leptogenesis with small violation ofb-l.Journal of Cosmology and Astroparticle Physics, 2012(07):030–030, July 2012
work page 2012
- [47]
-
[48]
Baker, Ansh Bhatnagar, Djuna Croon, and Jessica Turner
Michael J. Baker, Ansh Bhatnagar, Djuna Croon, and Jessica Turner. Hot leptogenesis, 2024
work page 2024
-
[49]
A. Granelli, K. Moffat, Y.F. Perez-Gonzalez, H. Schulz, and J. Turner. Ulysses: Universal leptogenesis equation solver.Computer Physics Communications, 262:107813, May 2021
work page 2021
-
[50]
A. Granelli, C. Leslie, Y.F. Perez-Gonzalez, H. Schulz, B. Shuve, J. Turner, and R. Walker. Ulysses, universal leptogenesis equation solver: Version 2.Computer Physics Communications, 291:108834, October 2023
work page 2023
-
[51]
Jones, Pasquale Di Bari, and Luca Marzola
Steve Blanchet, David A. Jones, Pasquale Di Bari, and Luca Marzola. Leptogenesis with heavy neutrino flavours: from density matrix to boltzmann equations, 2013
work page 2013
-
[52]
Satyabrata Datta, Anish Ghoshal, Angus Spalding, and Graham White. Gravitational wave spectral shapes as a probe of long lived right-handed neutrinos, leptogenesis and dark matter: Gobal versus local b-l cosmic strings, 2025
work page 2025
-
[53]
Anish Ghoshal, Angus Spalding, and Graham White. Cosmic strings gravitational wave probe of leptogenesis: Thermal, non-thermal, near-resonant and flavourful, 2025. 30
work page 2025
-
[54]
Pasquale Di Bari. An introduction to leptogenesis and neutrino properties.Contemporary Physics, 53(4):315–338, July 2012
work page 2012
- [55]
-
[56]
Planck Collaboration. Planck2018 results: Vi. cosmological parameters.Astronomy &; As- trophysics, 641:A6, September 2020
work page 2020
-
[57]
P. A. Zyla et al. Review of Particle Physics.PTEP, 2020(8):083C01, 2020
work page 2020
-
[58]
Leptogenesis in the universe.Advances in High Energy Physics, 2012:1–59, 2012
Chee Sheng Fong, Enrico Nardi, and Antonio Riotto. Leptogenesis in the universe.Advances in High Energy Physics, 2012:1–59, 2012
work page 2012
- [59]
-
[60]
E. Kh. Akhmedov, V. A. Rubakov, and A. Yu. Smirnov. Baryogenesis via neutrino oscillations. Physical Review Letters, 81(7):1359–1362, August 1998
work page 1998
-
[61]
Daniel J. H. Chung, Edward W. Kolb, and Antonio Riotto. Production of massive particles during reheating.Phys. Rev. D, 60:063504, 1999. 31
work page 1999
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