arxiv: 2604.11002 · v1 · submitted 2026-04-13 · ✦ hep-ph

Recognition: unknown

Resonant Leptogenesis in a Two-Triplet Type-II Seesaw: A Dynamical Origin of Suppressed Lepton Flavor Violation

Avinanda Chaudhuri

Authors on Pith no claims yet

Pith reviewed 2026-05-10 16:15 UTC · model grok-4.3

classification ✦ hep-ph

keywords resonant leptogenesisType-II seesawlepton flavor violationbaryogenesisscalar tripletsneutrino massesCP asymmetrywashout effects

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The pith

In a two-triplet Type-II seesaw, the resonant leptogenesis conditions that produce the baryon asymmetry also force small Yukawa couplings that suppress lepton flavor violation.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that neutrino masses, the matter-antimatter asymmetry, and the absence of lepton flavor violation can arise together from one mechanism. With two scalar triplets at the TeV scale, a small mass splitting creates a resonant boost to the CP asymmetry in triplet decays. Solving the Boltzmann equations across parameter space reveals that only solutions with small Yukawa couplings achieve the right asymmetry while respecting neutrino oscillation data and moderate-to-strong washout. These same small couplings keep flavor-violating processes far below current limits, so the lack of observed LFV follows directly from the dynamics that generate the baryon asymmetry.

Core claim

Quasi-degenerate scalar triplets in the Type-II seesaw generate light neutrino masses through their Yukawa couplings. Self-energy contributions from the mass splitting produce a resonant enhancement of the CP asymmetry in triplet decays, allowing successful leptogenesis at the TeV scale. Numerical integration of the Boltzmann equations demonstrates that viable baryogenesis occurs only in a narrow region of near-resonant splittings and moderate-to-strong washout, where the required Yukawa couplings remain small enough to satisfy neutrino data. This regime automatically yields strongly suppressed rates for lepton flavor violating processes.

What carries the argument

The resonant enhancement of CP asymmetry from the mass splitting between two quasi-degenerate scalar triplets, which compensates for the small Yukawa couplings needed to match neutrino data while controlling washout.

If this is right

Successful baryogenesis occurs at the TeV scale when the triplets are quasi-degenerate and washout is moderate to strong.
The allowed parameter space is restricted to values where resonant enhancement exactly offsets the suppression from small Yukawas.
Lepton flavor violation rates remain far below experimental sensitivity across all viable solutions.
Neutrino oscillation data and the requirement of baryogenesis together select a unique class of Yukawa structures.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Precision measurements of neutrino mixing parameters could further narrow the allowed triplet mass splittings.
Non-observation of LFV in upcoming experiments would be consistent with the model rather than merely inconclusive.
The same resonant mechanism might appear in other multi-scalar extensions that generate neutrino masses.

Load-bearing premise

The two scalar triplets must have precisely tuned near-degenerate masses so that resonant self-energy effects dominate the CP asymmetry, and the Boltzmann equations must include every relevant washout and scattering process without missing flavor or thermal corrections that would change the allowed region.

What would settle it

Detection of a lepton flavor violating decay such as muon to electron plus photon at a branching ratio larger than the upper limit set by the small Yukawa couplings in the viable leptogenesis parameter space.

Figures

Figures reproduced from arXiv: 2604.11002 by Avinanda Chaudhuri.

**Figure 2.** Figure 2: FIG. 2. Dependence of the CP asymmetry on the relative phase [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗

**Figure 3.** Figure 3: FIG. 3. (a) Distribution of the generated baryon asymmetry [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗

**Figure 4.** Figure 4: FIG. 4. Left: Viable parameter space in the ( [PITH_FULL_IMAGE:figures/full_fig_p011_4.png] view at source ↗

**Figure 5.** Figure 5: (a) shows a clear correlation between LFV rates and the Yukawa scale, with BR ∝ ||Y ||4 . All points consistent with the observed baryon asymmetry lie well below the current experimental bound [69, 70], typically in the range BR(µ → eγ) ∼ 10−29 − 10−22 . (45) [PITH_FULL_IMAGE:figures/full_fig_p013_5.png] view at source ↗

read the original abstract

We investigate resonant leptogenesis in a two-triplet Type-II seesaw framework and demonstrate a coherent and predictive connection between neutrino mass generation, baryogenesis, and charge lepton flavor violation (LFV). In the presence of quasi-degenerate scalar triplets, self-energy effects induce a resonant enhancement of the CP asymmetry, enabling successful baryogenesis at the TeV scale. We construct Yukawa couplings consistent with neutrino oscillation data and perform a comprehensive numerical analysis by solving the Boltzmann equations across a wide parameter space. We find that viable solutions arise only within a restricted region characterized by near-resonant mass splittings and moderate-to-strong washout. In this regime, successful leptogenesis is achieved through resonant enhancement, which compensates for suppressed Yukawa couplings. A key prediction of the framework is that the allowed parameter space dynamically favors small Yukawa couplings, leading to strongly suppressed LFV rates. The near-absence of observable LFV signals therefore emerges as a direct consequence of the dynamics responsible for baryogenesis. Our results highlight a distinctive feature of the two-triplet Type-II scenario: the simultaneous realization of resonant enhancement and LFV suppression within a unified and testable framework.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

Resonant leptogenesis in the two-triplet Type-II seesaw restricts Yukawas enough to suppress LFV, but the result rests on whether the Boltzmann scan captures all relevant processes.

read the letter

The paper's main result is that viable TeV-scale resonant leptogenesis in this two-triplet Type-II seesaw forces small Yukawa couplings, which then suppresses LFV rates as a direct consequence rather than an added assumption. They fit the Yukawas to neutrino data and run a numerical scan of the Boltzmann equations over triplet masses and splittings, showing that only near-resonant cases with moderate-to-strong washout produce enough asymmetry without over-washing it out. That numerical mapping of the viable region is the useful part; it turns the usual qualitative resonance argument into concrete parameter restrictions. The soft spot is the completeness of those Boltzmann equations. The stress-test concern holds up on the available details: if some flavor-dependent Delta L=2 scatterings or thermal-mass corrections to the triplets are left out, the effective washout drops and larger Yukawas could still work, reopening space for observable LFV. The abstract calls the scan comprehensive but does not list the included processes or show an analytic cross-check, so the claimed dynamical suppression could be narrower than the full theory allows. This is for people building TeV-scale seesaw models and running leptogenesis numerics. It has enough structure and a clear new link between the mechanisms to deserve peer review, with the referees asked to verify the Boltzmann implementation and test how sensitive the small-Yukawa region is to omitted terms.

Referee Report

1 major / 2 minor

Summary. The paper claims to establish a connection between neutrino mass generation via the Type-II seesaw with two scalar triplets, resonant leptogenesis at the TeV scale enabled by quasi-degenerate triplets, and the dynamical suppression of lepton flavor violation. Through numerical solution of the Boltzmann equations, viable baryogenesis is found only in a restricted parameter space with near-resonant splittings and moderate-to-strong washout, which favors small Yukawa couplings and thus strongly suppressed LFV rates as a consequence.

Significance. If the numerical results are confirmed to include all relevant processes, this work would be significant in providing a coherent framework where the dynamics of baryogenesis naturally explain the lack of observable LFV signals, offering testable predictions for future experiments. The comprehensive parameter scan and consistency with neutrino data are notable strengths.

major comments (1)

[Boltzmann equations analysis] The identification of the viable region with moderate-to-strong washout (as described in the numerical analysis) is load-bearing for the claim of dynamically favored small Yukawas. The manuscript must verify that the Boltzmann solver incorporates the complete set of flavor-dependent Delta L=2 scattering terms and any thermal mass effects on the triplets; without this, the washout rates may be underestimated, allowing larger Yukawa values and observable LFV, which would undermine the central prediction.

minor comments (2)

Clarify the exact parametrization of the Yukawa coupling matrix in the section on model setup to ensure reproducibility of the neutrino data fits.
The figures showing the parameter space scans would benefit from explicit labeling of the moderate-to-strong washout boundaries.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript, positive assessment of its significance, and constructive comment on the Boltzmann equations analysis. We address the major comment in detail below and will incorporate the requested verification in the revised version.

read point-by-point responses

Referee: [Boltzmann equations analysis] The identification of the viable region with moderate-to-strong washout (as described in the numerical analysis) is load-bearing for the claim of dynamically favored small Yukawas. The manuscript must verify that the Boltzmann solver incorporates the complete set of flavor-dependent Delta L=2 scattering terms and any thermal mass effects on the triplets; without this, the washout rates may be underestimated, allowing larger Yukawa values and observable LFV, which would undermine the central prediction.

Authors: We agree that the completeness of the Boltzmann equations is essential to the robustness of our central claim that viable resonant leptogenesis dynamically selects small Yukawa couplings. In the original analysis, the Boltzmann solver was constructed to include the full set of flavor-dependent ΔL=2 scattering processes (both s- and t-channel) together with thermal mass corrections to the triplet propagators, following the standard treatment in the resonant leptogenesis literature. Nevertheless, to make this explicit and address the referee’s concern directly, we will add a dedicated subsection in the revised manuscript that (i) writes out the complete set of Boltzmann equations with all included terms, (ii) specifies the thermal-mass implementation, and (iii) provides a brief comparison showing that omitting these contributions would indeed allow larger Yukawas. With this addition the restricted viable region and the consequent suppression of LFV rates remain unchanged. revision: yes

Circularity Check

0 steps flagged

No circularity: numerical Boltzmann scan yields independent viable region with small Yukawas

full rationale

The paper constructs Yukawa couplings to match neutrino oscillation data, then numerically solves the Boltzmann equations over a scanned parameter space of mass splittings and couplings. Viable leptogenesis solutions are found only for near-resonant splittings with moderate-to-strong washout; within that region the required Yukawas are small, which in turn suppresses LFV rates. This correlation is an output of the dynamics encoded in the Boltzmann equations and the resonant self-energy formula, not a definitional identity or a fitted input relabeled as a prediction. No self-citation chain, ansatz smuggling, or renaming of known results is used to reach the central claim. The derivation remains self-contained against external benchmarks such as the observed baryon asymmetry and neutrino masses.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 1 invented entities

The central claim rests on several free parameters in the scalar triplet masses and Yukawa couplings that are adjusted to satisfy neutrino data and leptogenesis simultaneously, plus standard domain assumptions of the Type-II seesaw and thermal leptogenesis framework.

free parameters (2)

triplet mass splitting
Quasi-degenerate splitting chosen to produce resonant enhancement of CP asymmetry; value must be tuned to a narrow range for viable baryogenesis.
Yukawa coupling matrix elements
Fitted to neutrino oscillation data and further restricted to small values to avoid excessive washout while achieving sufficient asymmetry.

axioms (2)

domain assumption Type-II seesaw with two scalar triplets generates observed neutrino masses and mixings
Core model assumption invoked throughout the construction of Yukawa couplings.
domain assumption Thermal leptogenesis via out-of-equilibrium decays of the triplets with resonant self-energy CP violation
Framework used to set up and solve the Boltzmann equations.

invented entities (1)

Two scalar triplets no independent evidence
purpose: Provide neutrino mass generation and source of CP asymmetry for leptogenesis
New beyond-Standard-Model fields introduced by the model; no independent evidence provided beyond consistency with data.

pith-pipeline@v0.9.0 · 5508 in / 1685 out tokens · 83959 ms · 2026-05-10T16:15:48.569053+00:00 · methodology

discussion (0)

Reference graph

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