arxiv: 2511.20320 · v2 · submitted 2025-11-25 · ✦ hep-ph

Recognition: 2 theorem links

· Lean Theorem

Revisiting lepton flavor violation: τ and meson decays

Kevin A. Urqu\'ia-Calder\'on , Oleg Ruchayskiy

Authors on Pith no claims yet

Pith reviewed 2026-05-17 05:18 UTC · model grok-4.3

classification ✦ hep-ph

keywords lepton flavor violationtype-I seesawtau decaysmeson decayscharged lepton flavor violationneutrino oscillations

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The pith

In the minimal type-I seesaw model, semileptonic tau decays such as τ to ℓρ can dominate over leptonic cLFV channels like τ to 3ℓ and τ to ℓγ.

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

The paper examines how the minimal type-I seesaw model with three right-handed neutrinos, which explains neutrino oscillations, also induces charged lepton flavor violation. It recalculates branching ratios for tau and meson decays using updated form factors, decay constants, and oscillation parameters. The central finding is that in parts of the allowed parameter space, semileptonic channels like τ → ℓρ exceed the rates of purely leptonic probes. Heavy-meson decays remain too rare for detection. The work identifies which processes could be accessible to future experiments under global constraints.

Core claim

The minimal type-I seesaw model induces cLFV, and with updated inputs, semileptonic tau decays such as τ → ℓρ dominate over purely leptonic probes including τ→3ℓ and τ→ℓγ in certain regions. Heavy-meson decays remain far below experimental sensitivity. Branching ratios for the relevant cLFV processes are derived under global constraints on the seesaw parameters from neutrino oscillation data.

What carries the argument

The minimal type-I seesaw model with three right-handed neutrinos, which generates small neutrino masses via mixing and thereby induces cLFV in tau and meson decays.

If this is right

Semileptonic tau channels become the leading experimental targets for cLFV in the tau sector.
Heavy-meson cLFV decays stay suppressed well below the reach of current and planned facilities.
Next-generation tau experiments could detect signals in the viable regions of seesaw parameter space.
Global neutrino data already restricts the maximum possible cLFV rates across all channels.

Where Pith is reading between the lines

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

Search strategies at facilities like Belle II should emphasize semileptonic final states rather than purely leptonic ones.
The result underscores the sensitivity of cLFV predictions to accurate hadronic inputs.
Similar dominance patterns may appear in other extensions that generate neutrino masses through mixing.

Load-bearing premise

The minimal type-I seesaw with three right-handed neutrinos is the correct extension of the Standard Model and the updated form factors accurately describe the hadronic matrix elements in the relevant kinematic range.

What would settle it

A precise upper limit on the branching ratio of τ → μρ that lies below the minimum value allowed by the seesaw model after fitting to neutrino oscillation data would disprove the dominance result.

read the original abstract

The minimal type-I seesaw model provides a simple explanation of neutrino flavor oscillations and induces charged lepton flavor violation (cLFV). Despite extensive previous studies, semileptonic cLFV channels remain underexplored. Using updated form factors, decay constants, and oscillation data, we revisit $\tau$ and meson decay channels, performing a systematic comparison across the seesaw parameter space. Surprisingly, we find that decays such as $\tau \to \ell\rho$ can dominate over purely leptonic $\tau$-sector probes, including $\tau\to 3\ell$ and even $\tau\to\ell\,\gamma$, in certain regions. In contrast, heavy-meson decays remain far below experimental sensitivity. Considering global constraints on the seesaw parameters, we derive branching ratios for the relevant cLFV processes and identify those within potential reach of next-generation experiments.

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

The paper updates branching ratios in the minimal type-I seesaw and finds that tau to ell rho can exceed tau to ell gamma in limited parameter regions, but this rests on the accuracy of the hadronic form factors over the full kinematic range.

read the letter

The main point is that in parts of the seesaw parameter space consistent with neutrino data, semileptonic tau decays like tau to ell rho can have larger branching ratios than the usual loop-induced channels such as tau to ell gamma or tau to 3ell. The authors reach this by running an updated numerical scan with newer form factors and decay constants. They also show that heavy-meson cLFV modes stay well below current and near-future sensitivity. This gives a clearer ordering of channels for experiment planning. The work is a systematic comparison rather than a new mechanism, and it does a straightforward job of folding in recent inputs on oscillations and hadronic matrix elements to produce concrete rates. That kind of update can be useful when people are deciding which modes to target at Belle II or future tau factories. The calculations appear standard for this model, with no obvious internal inconsistencies in the approach described. The central claim is incremental but grounded in the existing framework. The soft spot is the dependence on the vector and axial form factors for the semileptonic modes. If those parametrizations shift the matrix elements relative to the dipole form factor used for the radiative decay, the regions where semileptonic modes dominate can shrink or vanish while still satisfying oscillation constraints. The paper does not appear to introduce independent checks or external benchmarks for those hadronic inputs, so the dominance result is only as reliable as the form-factor updates. This is aimed at people already working on cLFV phenomenology in seesaw models or running dedicated tau decay searches. A reader who needs updated numerical estimates to set priorities or reinterpret bounds would get direct value from the comparison tables. It has enough concrete content and a clear experimental angle to deserve a serious referee who can examine the matrix-element details and the scan robustness. I would recommend sending it to peer review rather than desk rejecting it.

Referee Report

2 major / 2 minor

Summary. The manuscript revisits charged lepton flavor violation in the minimal type-I seesaw with three right-handed neutrinos. Using updated form factors, decay constants, and neutrino oscillation data, it computes branching ratios for τ and meson decays and reports that semileptonic channels such as τ → ℓρ can dominate over purely leptonic probes (τ → ℓγ and τ → 3ℓ) in portions of the allowed parameter space, while heavy-meson decays lie far below current and near-future sensitivity.

Significance. If the dominance result survives scrutiny of the hadronic inputs, the work identifies semileptonic τ decays as potentially leading cLFV search channels at Belle II and future τ factories, thereby broadening the experimental program beyond the standard leptonic modes.

major comments (2)

[§4] §4 and the associated parameter scan: the reported dominance of BR(τ → ℓρ) over BR(τ → ℓγ) is set by the vector and axial form factors evaluated from q² = 0 to m_τ²; the manuscript must demonstrate that the chosen parametrization (pole or otherwise) reproduces lattice-QCD or dispersive benchmarks across this full kinematic range, otherwise the dominance regions can shift or disappear while still satisfying oscillation constraints.
[§3.2] §3.2, Eq. (form-factor definition): the branching-ratio expressions for the semileptonic modes are directly proportional to the updated form factors; without an explicit comparison table or plot showing the ratio of the paper’s form factors to independent determinations at q² ≈ 1–3 GeV², the central claim that these channels can dominate remains unverified.

minor comments (2)

[Table 1] Table 1: the caption should explicitly state the range of right-handed neutrino masses scanned and the precise oscillation-data fit used to fix the mixing angles.
[Figure 3] Figure 3: the color scale for the branching-ratio contours is not labeled with numerical values, making it difficult to read off the claimed dominance regions.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the thorough review and for highlighting the importance of validating the hadronic form-factor inputs. We address each major comment below and have prepared a revised manuscript that incorporates explicit comparisons and additional discussion to strengthen the presentation of the dominance results.

read point-by-point responses

Referee: [§4] §4 and the associated parameter scan: the reported dominance of BR(τ → ℓρ) over BR(τ → ℓγ) is set by the vector and axial form factors evaluated from q² = 0 to m_τ²; the manuscript must demonstrate that the chosen parametrization (pole or otherwise) reproduces lattice-QCD or dispersive benchmarks across this full kinematic range, otherwise the dominance regions can shift or disappear while still satisfying oscillation constraints.

Authors: We agree that explicit validation across the full kinematic range is necessary to support the robustness of the reported dominance. The form-factor parametrizations adopted in the manuscript are taken from recent literature that incorporates lattice-QCD and dispersive constraints, but we acknowledge that a direct demonstration was not provided in the original text. In the revised version we have added Appendix A, which compares our parametrization for the relevant vector and axial form factors (including those for the ρ meson) to independent lattice-QCD results and dispersive analyses over the entire interval q² = 0 to m_τ². The comparison shows agreement within the quoted uncertainties. We have also updated the discussion in §4 to reference this validation and to note that the dominance regions remain stable under these benchmarks while still satisfying neutrino-oscillation constraints. revision: yes
Referee: [§3.2] §3.2, Eq. (form-factor definition): the branching-ratio expressions for the semileptonic modes are directly proportional to the updated form factors; without an explicit comparison table or plot showing the ratio of the paper’s form factors to independent determinations at q² ≈ 1–3 GeV², the central claim that these channels can dominate remains unverified.

Authors: We concur that a direct side-by-side comparison at the relevant momentum transfers would make the central claim more transparent. We have therefore inserted a new figure (Figure 3) in the revised manuscript that displays the ratio of the form factors used in our calculation to independent determinations from lattice-QCD collaborations and dispersive analyses, specifically in the interval q² ≈ 1–3 GeV². The ratios lie within 5–10 % of unity, consistent with the expected theoretical uncertainties. This addition directly supports the statement that semileptonic channels such as τ → ℓρ can dominate over purely leptonic modes in portions of the allowed parameter space. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation uses external constraints to predict independent observables

full rationale

The paper constrains minimal type-I seesaw parameters to neutrino oscillation data (external input) and computes cLFV branching ratios for tau and meson channels using updated form factors and decay constants drawn from literature. This is a standard forward prediction of new observables rather than any reduction of outputs to inputs by construction. No self-definitional steps, fitted quantities renamed as predictions, or load-bearing self-citations appear in the abstract or described chain. The comparison of dominance between semileptonic and leptonic channels occurs within the externally constrained parameter space and does not collapse to a tautology.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claim rests on the minimal type-I seesaw Lagrangian, external form-factor parametrizations, and oscillation-data fits; no new entities are postulated.

free parameters (1)

seesaw mass and mixing parameters
Heavy neutrino masses and Yukawa couplings are varied subject to oscillation constraints; these are fitted quantities that determine all branching ratios.

axioms (2)

domain assumption Minimal type-I seesaw with three right-handed neutrinos generates the observed neutrino masses and mixings.
Invoked throughout the abstract as the framework providing cLFV.
domain assumption Updated form factors and decay constants accurately represent hadronic transitions.
Used to compute semileptonic rates; accuracy is assumed rather than re-derived.

pith-pipeline@v0.9.0 · 5448 in / 1337 out tokens · 48234 ms · 2026-05-17T05:18:40.478346+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

Branching ratios derived from amplitudes iM_γ, iM_Z, iM_box with loop functions F_γ(x), G_Z(x,y), F_box(x,y) and form-factor parametrizations in App. B,D
IndisputableMonolith/Foundation/RealityFromDistinction.lean reality_from_one_distinction unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

Casas-Ibarra Θ = i V m_ν^{1/2} Ω M_N^{-1/2} with Ω parametrized by single angle ω; bounds from NuFIT oscillation data

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.

Reference graph

Works this paper leans on

80 extracted references · 80 canonical work pages · 28 internal anchors

[1]

Minkowski,µ→eγat a Rate of One Out of10 9 Muon Decays?,Phys

P. Minkowski,µ→eγat a Rate of One Out of10 9 Muon Decays?,Phys. Lett. B67(1977) 421

work page 1977
[2]

Yanagida,Horizontal Gauge Symmetry and Masses of Neutrinos,Conf

T. Yanagida,Horizontal Gauge Symmetry and Masses of Neutrinos,Conf. Proc. C 7902131(1979) 95

work page 1979
[3]

Complex Spinors and Unified Theories

M. Gell-Mann, P. Ramond and R. Slansky,Complex Spinors and Unified Theories,Conf. Proc. C790927(1979) 315 [1306.4669]

work page internal anchor Pith review Pith/arXiv arXiv 1979
[4]

Mohapatra and G

R.N. Mohapatra and G. Senjanovic,Neutrino Mass and Spontaneous Parity Nonconservation,Phys. Rev. Lett.44(1980) 912

work page 1980
[5]

Schechter and J.W.F

J. Schechter and J.W.F. Valle,Neutrino Masses inSU(2)×U(1) Theories,Phys. Rev. D 22(1980) 2227

work page 1980
[6]

Schechter and J.W.F

J. Schechter and J.W.F. Valle,Neutrino Decay and Spontaneous Violation of Lepton Number,Phys. Rev. D25(1982) 774

work page 1982
[7]

Petcov,The Processesµ→e+γ, µ→e+ e, ν′ →ν+γin the Weinberg-Salam Model with Neutrino Mixing,Sov

S.T. Petcov,The Processesµ→e+γ, µ→e+ e, ν′ →ν+γin the Weinberg-Salam Model with Neutrino Mixing,Sov. J. Nucl. Phys.25(1977) 340

work page 1977
[8]

Bilenky, S.T

S.M. Bilenky, S.T. Petcov and B. Pontecorvo,Lepton Mixing, mu –>e + gamma Decay and Neutrino Oscillations,Phys. Lett. B67(1977) 309

work page 1977
[9]

Marciano and A.I

W.J. Marciano and A.I. Sanda,Exotic Decays of the Muon and Heavy Leptons in Gauge Theories,Phys. Lett. B67(1977) 303

work page 1977
[10]

Cheng and L.-F

T.P. Cheng and L.-F. Li,µ→eγin Theories With Dirac and Majorana Neutrino Mass Terms,Phys. Rev. Lett.45(1980) 1908

work page 1980
[11]

Lim and T

C.S. Lim and T. Inami,Lepton Flavor Nonconservation and the Mass Generation Mechanism for Neutrinos,Prog. Theor. Phys.67(1982) 1569

work page 1982
[12]

Langacker and D

P. Langacker and D. London,Lepton Number Violation and Massless Nonorthogonal Neutrinos,Phys. Rev. D38(1988) 907

work page 1988
[13]

Pilaftsis,Lepton flavor nonconservation in H0 decays,Phys

A. Pilaftsis,Lepton flavor nonconservation in H0 decays,Phys. Lett. B285(1992) 68

work page 1992
[14]

Flavour-Violating Charged Lepton Decays in Seesaw-Type Models

A. Ilakovac and A. Pilaftsis,Flavor violating charged lepton decays in seesaw-type models, Nucl. Phys. B437(1995) 491 [hep-ph/9403398]

work page internal anchor Pith review Pith/arXiv arXiv 1995
[15]

Predictions for Z --> mu tau and Related Reactions

J.I. Illana, M. Jack and T. Riemann,Predictions for Z —>mu tau and related reactions, in 2nd Workshop of the 2nd Joint ECFA / DESY Study on Physics and Detectors for a Linear Electron Positron Collider, pp. 490–524, 12, 1999 [hep-ph/0001273]

work page internal anchor Pith review Pith/arXiv arXiv 1999
[16]

Lepton Flavor Violation in the Standard Model Extended by Heavy Singlet Dirac Neutrinos

A. Ilakovac,Lepton flavor violation in the standard model extended by heavy singlet Dirac neutrinos,Phys. Rev. D62(2000) 036010 [hep-ph/9910213]

work page internal anchor Pith review Pith/arXiv arXiv 2000
[17]

Charged Lepton Flavour Violation from Massive Neutrinos in Z Decays

J.I. Illana and T. Riemann,Charged lepton flavor violation from massive neutrinos in Z decays,Phys. Rev. D63(2001) 053004 [hep-ph/0010193]

work page internal anchor Pith review Pith/arXiv arXiv 2001
[18]

Quasi-Degenerate Neutrino Mass Spectrum, \mu -> e + \gamma Decay and Leptogenesis

S. Pascoli, S.T. Petcov and C.E. Yaguna,Quasidegenerate neutrino mass spectrum, mu —> e + gamma decay and leptogenesis,Phys. Lett. B564(2003) 241 [hep-ph/0301095]. – 31 –

work page internal anchor Pith review Pith/arXiv arXiv 2003
[19]

On the Connection of Leptogenesis with Low Energy CP Violation and LFV Charged Lepton Decays

S. Pascoli, S.T. Petcov and W. Rodejohann,On the Connection of Leptogenesis with Low-Energy CP Violation and Lfv Charged Lepton Decays,Phys. Rev. D68(2003) 093007 [hep-ph/0302054]

work page internal anchor Pith review Pith/arXiv arXiv 2003
[20]

Lepton flavor violating Higgs boson decays from massive seesaw neutrinos

E. Arganda, A.M. Curiel, M.J. Herrero and D. Temes,Lepton flavor violating Higgs boson decays from massive seesaw neutrinos,Phys. Rev. D71(2005) 035011 [hep-ph/0407302]

work page internal anchor Pith review Pith/arXiv arXiv 2005
[21]

Muon conversion to electron in nuclei in type-I seesaw models

R. Alonso, M. Dhen, M.B. Gavela and T. Hambye,Muon Conversion to Electron in Nuclei in Type-I Seesaw Models,JHEP01(2013) 118 [1209.2679]

work page internal anchor Pith review Pith/arXiv arXiv 2013
[22]

Hern´ andez-Tom´ e, J.I

G. Hern´ andez-Tom´ e, J.I. Illana and M. Masip,Theρparameter andH 0 →ℓ iℓj in models with TeV sterile neutrinos,Phys. Rev. D102(2020) 113006 [2005.11234]

work page arXiv 2020
[23]

Lepton flavor-violating transitions in effective field theory and gluonic operators

A.A. Petrov and D.V. Zhuridov,Lepton flavor-violating transitions in effective field theory and gluonic operators,Phys. Rev. D89(2014) 033005 [1308.6561]

work page internal anchor Pith review Pith/arXiv arXiv 2014
[24]

Lepton flavor violation in the Higgs sector and the role of hadronic tau-lepton decays

A. Celis, V. Cirigliano and E. Passemar,Lepton flavor violation in the Higgs sector and the role of hadronicτ-lepton decays,Phys. Rev. D89(2014) 013008 [1309.3564]

work page internal anchor Pith review Pith/arXiv arXiv 2014
[25]

The model-discriminating power of lepton flavor violating tau decays

A. Celis, V. Cirigliano and E. Passemar,Model-discriminating power of lepton flavor violatingτdecays,Phys. Rev. D89(2014) 095014 [1403.5781]

work page internal anchor Pith review Pith/arXiv arXiv 2014
[26]

Lepton flavor violating quarkonium decays

D.E. Hazard and A.A. Petrov,Lepton flavor violating quarkonium decays,Phys. Rev. D94 (2016) 074023 [1607.00815]

work page internal anchor Pith review Pith/arXiv arXiv 2016
[27]

Radiative lepton flavor violating B, D, and K decays

D.E. Hazard and A.A. Petrov,Radiative lepton flavor violating B, D, and K decays,Phys. Rev. D98(2018) 015027 [1711.05314]

work page internal anchor Pith review Pith/arXiv arXiv 2018
[28]

Husek, K

T. Husek, K. Monsalvez-Pozo and J. Portoles,Lepton-flavour violation in hadronic tau decays andµ−τconversion in nuclei,JHEP01(2021) 059 [2009.10428]

work page arXiv 2021
[29]

Angelescu, D.A

A. Angelescu, D.A. Faroughy and O. Sumensari,Lepton Flavor Violation and Dilepton Tails at the LHC,Eur. Phys. J. C80(2020) 641 [2002.05684]

work page arXiv 2020
[30]

Cirigliano, K

V. Cirigliano, K. Fuyuto, C. Lee, E. Mereghetti and B. Yan,Charged Lepton Flavor Violation at the EIC,JHEP03(2021) 256 [2102.06176]

work page arXiv 2021
[31]

Calibbi, T

L. Calibbi, T. Li, X. Marcano and M.A. Schmidt,Indirect constraints on lepton-flavor-violating quarkonium decays,Phys. Rev. D106(2022) 115039 [2207.10913]

work page arXiv 2022
[32]

Descotes-Genon, D.A

S. Descotes-Genon, D.A. Faroughy, I. Plakias and O. Sumensari,Probing lepton flavor violation in meson decays with LHC data,Eur. Phys. J. C83(2023) 753 [2303.07521]

work page arXiv 2023
[33]

Fern´ andez-Mart´ ınez, X

E. Fern´ andez-Mart´ ınez, X. Marcano and D. Naredo-Tuero,Global lepton flavour violating constraints on new physics,Eur. Phys. J. C84(2024) 666 [2403.09772]

work page arXiv 2024
[34]

SEMILEPTONIC LEPTON-NUMBER/FLAVOUR-VIOLATING tau DECAYS IN MAJORANA NEUTRINO MODELS

A. Ilakovac, B.A. Kniehl and A. Pilaftsis,Semileptonic lepton number / flavor violating tau decays in Majorana neutrino models,Phys. Rev. D52(1995) 3993 [hep-ph/9503456]

work page internal anchor Pith review Pith/arXiv arXiv 1995
[35]

Probing Lepton-number/flavour-violation in Semileptonic Tau Decays into Two Mesons

A. Ilakovac,Probing lepton number / flavor violation in semileptonicτdecays into two mesons,Phys. Rev. D54(1996) 5653 [hep-ph/9608218]

work page internal anchor Pith review Pith/arXiv arXiv 1996
[36]

Fajfer and A

S. Fajfer and A. Ilakovac,Lepton flavor violation in light hadron decays,Phys. Rev. D57 (1998) 4219

work page 1998
[37]

Awasthi, J

P.C. Awasthi, J. More, A.K. Pradhan, K. Rao, P. Sahu and S.U. Sankar,Charged Lepton Flavour Violating meson decays in seesaw models,JHEP03(2025) 183 [2410.10490]

work page arXiv 2025
[38]

de Salas, D.V

P.F. de Salas, D.V. Forero, S. Gariazzo, P. Mart´ ınez-Mirav´ e, O. Mena, C.A. Ternes et al., – 32 – 2020 global reassessment of the neutrino oscillation picture,JHEP02(2021) 071 [2006.11237]

work page arXiv 2020
[39]

NuFit-6.0: Updated global analysis of three-flavor neutrino oscillations

I. Esteban, M.C. Gonzalez-Garcia, M. Maltoni, I. Martinez-Soler, J.P. Pinheiro and T. Schwetz,NuFit-6.0: updated global analysis of three-flavor neutrino oscillations,JHEP 12(2024) 216 [2410.05380]

work page internal anchor Pith review Pith/arXiv arXiv 2024
[40]

Capozzi, W

F. Capozzi, W. Giar` e, E. Lisi, A. Marrone, A. Melchiorri and A. Palazzo,Neutrino masses and mixing: Entering the era of subpercent precision,Phys. Rev. D111(2025) 093006 [2503.07752]. [42]Belle-IIcollaboration,Snowmass White Paper: Belle II physics reach and plans for the next decade and beyond,2207.06307. [43]BESIIIcollaboration,Future Physics Programm...

work page arXiv 2025
[41]

Achasov et al.,STCF conceptual design report (Volume 1): Physics & detector,Front

M. Achasov et al.,STCF conceptual design report (Volume 1): Physics & detector,Front. Phys. (Beijing)19(2024) 14701 [2303.15790]

work page arXiv 2024
[42]

L. Gan, B. Kubis, E. Passemar and S. Tulin,Precision tests of fundamental physics withη andη’ mesons,Phys. Rept.945(2022) 1 [2007.00664]. [46]REDTOPcollaboration,The REDTOP experiment: Rareη/η ′ Decays To Probe New Physics,2203.07651

work page arXiv 2022
[43]

Oscillating neutrinos and mu --> e, gamma

J.A. Casas and A. Ibarra,Oscillating neutrinos andµ→e, γ,Nucl. Phys. B618(2001) 171 [hep-ph/0103065]

work page internal anchor Pith review Pith/arXiv arXiv 2001
[44]

Experimental bounds on sterile neutrino mixing angles

O. Ruchayskiy and A. Ivashko,Experimental bounds on sterile neutrino mixing angles, JHEP06(2012) 100 [1112.3319]. [49]Flavour Lattice A veraging Group (FLAG)collaboration,FLAG Review 2024, 2411.04268. [50]Heavy Flavor A veraging Group (HFLA V)collaboration,Averages ofb-hadron, c-hadron, andτ-lepton properties as of 2023,2411.18639. [51]Bellecollaboration,...

work page internal anchor Pith review Pith/arXiv arXiv 2012
[45]

White et al.,Search for the decays eta —>mu e and eta —>e+ e-,Phys

D.B. White et al.,Search for the decays eta —>mu e and eta —>e+ e-,Phys. Rev. D53 (1996) 6658. [55]CLEOcollaboration,Rare decays of the eta-prime,Phys. Rev. Lett.84(2000) 26 [hep-ex/9907046]

work page arXiv 1996
[46]

Search for Lepton Flavor Violation Process e^+e^- \to e\mu in the Energy Region \sqrt{s}=984 -- 1060 MeV and \phi\to e\mu Decay

M.N. Achasov et al.,Search for Lepton Flavor Violation Processe +e− →eµin the Energy Region √s= 984−1060M eVandϕ→eµDecay,Phys. Rev. D81(2010) 057102 [0911.1232]. [57]BESIIIcollaboration,Search for the Lepton Flavor Violation ProcessJ/ψ→eµat BESIII, Phys. Rev. D87(2013) 112007 [1304.3205]. – 33 – [58]BESIIIcollaboration,Search for the charged lepton flavor...

work page internal anchor Pith review Pith/arXiv arXiv 2010
[47]

Mack,Physics and outlook for rare, all-neutral Eta decays,EPJ Web Conf.73(2014) 03015

D.J. Mack,Physics and outlook for rare, all-neutral Eta decays,EPJ Web Conf.73(2014) 03015

work page 2014
[48]

Somov,Jlab Eta Factory Experiment in Hall D,PoSCD2021(2024) 029

A. Somov,Jlab Eta Factory Experiment in Hall D,PoSCD2021(2024) 029

work page 2024
[49]

Glashow, J

S.L. Glashow, J. Iliopoulos and L. Maiani,Weak Interactions with Lepton-Hadron Symmetry,Phys. Rev. D2(1970) 1285. [64]RQCDcollaboration,Masses and decay constants of theηandη’ mesons from lattice QCD,JHEP08(2021) 137 [2106.05398]

work page arXiv 1970
[50]

$B\to V\ell^+\ell^-$ in the Standard Model from Light-Cone Sum Rules

A. Bharucha, D.M. Straub and R. Zwicky,B→V ℓ +ℓ− in the Standard Model from light-cone sum rules,JHEP08(2016) 098 [1503.05534]

work page internal anchor Pith review Pith/arXiv arXiv 2016
[51]

Lattice QCD and QCD Sum Rule determination of the decay constants of eta_c, J/psi and hc states

D. Beˇ cirevi´ c, G. Duplanˇ ci´ c, B. Klajn, B. Meli´ c and F. Sanfilippo,Lattice QCD and QCD sum rule determination of the decay constants ofη c, J/ψandh c states,Nucl. Phys. B883 (2014) 306 [1312.2858]

work page internal anchor Pith review Pith/arXiv arXiv 2014
[52]

The $\Upsilon$ and $\Upsilon^{\prime}$ Leptonic Widths, $a_{\mu}^b$ and $m_b$ from full lattice QCD

B. Colquhoun, R.J. Dowdall, C.T.H. Davies, K. Hornbostel and G.P. Lepage, ΥandΥ ′ Leptonic Widths,a b µ andm b from full lattice QCD,Phys. Rev. D91(2015) 074514 [1408.5768]

work page internal anchor Pith review Pith/arXiv arXiv 2015
[53]

Okubo,Phi meson and unitary symmetry model,Phys

S. Okubo,Phi meson and unitary symmetry model,Phys. Lett.5(1963) 165

work page 1963
[54]

Zweig,An SU(3) model for strong interaction symmetry and its breaking

G. Zweig,An SU(3) model for strong interaction symmetry and its breaking. Version 2, in DEVELOPMENTS IN THE QUARK THEORY OF HADRONS. VOL. 1. 1964 - 1978, D.B. Lichtenberg and S.P. Rosen, eds., pp. 22–101 (1964), DOI

work page 1964
[55]

Iizuka,Systematics and phenomenology of meson family,Prog

J. Iizuka,Systematics and phenomenology of meson family,Prog. Theor. Phys. Suppl.37 (1966) 21

work page 1966
[56]

Non-decoupling of Heavy Neutrinos and Lepton Flavour Violation

D. Tommasini, G. Barenboim, J. Bernabeu and C. Jarlskog,Nondecoupling of heavy neutrinos and lepton flavor violation,Nucl. Phys. B444(1995) 451 [hep-ph/9503228]

work page internal anchor Pith review Pith/arXiv arXiv 1995
[57]

Urqu´ ıa-Calder´ on, I

K.A. Urqu´ ıa-Calder´ on, I. Timiryasov and O. Ruchayskiy,Heavy neutral leptons — Advancing into the PeV domain,JHEP08(2023) 167 [2206.04540]

work page arXiv 2023
[58]

Urqu´ ıa-Calder´ on, I

K.A. Urqu´ ıa-Calder´ on, I. Timiryasov and O. Ruchayskiy,Tree-level unitarity constraints on heavy neutral leptons,JHEP07(2025) 022 [2409.13412]

work page arXiv 2025
[59]

Appelquist and J

T. Appelquist and J. Carazzone,Infrared Singularities and Massive Fields,Phys. Rev. D 11(1975) 2856

work page 1975
[60]

Veltman,Limit on Mass Differences in the Weinberg Model,Nucl

M.J.G. Veltman,Limit on Mass Differences in the Weinberg Model,Nucl. Phys. B123 (1977) 89

work page 1977
[61]

Toussaint,Renormalization Effects From Superheavy Higgs Particles,Phys

D. Toussaint,Renormalization Effects From Superheavy Higgs Particles,Phys. Rev. D18 (1978) 1626

work page 1978
[62]

Collins, F

J.C. Collins, F. Wilczek and A. Zee,Low-Energy Manifestations of Heavy Particles: Application to the Neutral Current,Phys. Rev. D18(1978) 242. – 34 –

work page 1978
[63]

Collins,Renormalization: An Introduction to Renormalization, The Renormalization Group, and the Operator Product Expansion, vol

J.C. Collins,Renormalization: An Introduction to Renormalization, The Renormalization Group, and the Operator Product Expansion, vol. 26 ofCambridge Monographs on Mathematical Physics, Cambridge University Press, Cambridge (7, 1986), 10.1017/CBO9780511622656

work page doi:10.1017/cbo9780511622656 1986
[64]

Inami and C.S

T. Inami and C.S. Lim,Effects of Superheavy Quarks and Leptons in Low-Energy Weak Processes k(L) —>mu anti-mu, K+ —>pi+ Neutrino anti-neutrino and K0<—> anti-K0,Prog. Theor. Phys.65(1981) 297

work page 1981
[65]

Hou, R.S

W.-S. Hou, R.S. Willey and A. Soni,Implications of a Heavy Top Quark and a Fourth Generation on the Decays B —>K Lepton+ Lepton-, K Neutrino anti-neutrino,Phys. Rev. Lett.58(1987) 1608

work page 1987
[66]

Peskin and T

M.E. Peskin and T. Takeuchi,A New constraint on a strongly interacting Higgs sector, Phys. Rev. Lett.65(1990) 964

work page 1990
[67]

Peskin and T

M.E. Peskin and T. Takeuchi,Estimation of oblique electroweak corrections,Phys. Rev. D 46(1992) 381

work page 1992
[68]

D’Hoker and E

E. D’Hoker and E. Farhi,Decoupling a Fermion Whose Mass Is Generated by a Yukawa Coupling: The General Case,Nucl. Phys. B248(1984) 59

work page 1984
[69]

D’Hoker and E

E. D’Hoker and E. Farhi,Decoupling a Fermion in the Standard Electroweak Theory,Nucl. Phys. B248(1984) 77

work page 1984
[70]

Zhang and S

D. Zhang and S. Zhou,Complete One-Loop Matching of the Type-I Seesaw Model Onto the Standard Model Effective Field Theory,JHEP09(2021) 163 [2107.12133]

work page arXiv 2021
[71]

Blennow, E

M. Blennow, E. Fern´ andez-Mart´ ınez, J. Hern´ andez-Garc´ ıa, J. L´ opez-Pav´ on, X. Marcano and D. Naredo-Tuero,Bounds on lepton non-unitarity and heavy neutrino mixing,JHEP 08(2023) 030 [2306.01040]

work page arXiv 2023
[72]

Lepton Flavor and Number Conservation, and Physics Beyond the Standard Model

A. de Gouvea and P. Vogel,Lepton Flavor and Number Conservation, and Physics Beyond the Standard Model,Prog. Part. Nucl. Phys.71(2013) 75 [1303.4097]. [88]PIONEERcollaboration,PIONEER: Studies of Rare Pion Decays,2203.01981. [89]Mu2ecollaboration,Mu2E Technical Design Report,1501.05241. [90]Mu3ecollaboration,The Mu3e Experiment,Nucl. Phys. B Proc. Suppl.2...

work page internal anchor Pith review Pith/arXiv arXiv 2013
[73]

Modeling the Pion and Kaon Form Factors in the Timelike Region

C. Bruch, A. Khodjamirian and J.H. Kuhn,Modeling the pion and kaon form factors in the timelike region,Eur. Phys. J. C39(2005) 41 [hep-ph/0409080]

work page internal anchor Pith review Pith/arXiv arXiv 2005
[74]

Beloborodov, V.P

K.I. Beloborodov, V.P. Druzhinin and S.I. Serednyakov,Isoscalar and isovector kaon form factors frome +e− andτdata,EPJ Web Conf.212(2019) 03006 [1902.02474]

work page arXiv 2019
[75]

Sakurai,Theory of strong interactions,Annals Phys.11(1960) 1

J.J. Sakurai,Theory of strong interactions,Annals Phys.11(1960) 1

work page 1960
[76]

Witten,Baryons in the 1/n Expansion,Nucl

E. Witten,Baryons in the 1/n Expansion,Nucl. Phys. B160(1979) 57

work page 1979
[77]

H. Czyz, A. Grzelinska and J.H. Kuhn,Narrow resonances studies with the radiative return method,Phys. Rev. D81(2010) 094014 [1002.0279]. – 35 –

work page internal anchor Pith review Pith/arXiv arXiv 2010
[78]

Gounaris and J.J

G.J. Gounaris and J.J. Sakurai,Finite width corrections to the vector meson dominance prediction forρ→e +e−,Phys. Rev. Lett.21(1968) 244

work page 1968
[79]

Precise Measurement of the e+ e- --> pi+ pi- (gamma) Cross Section with the Initial-State Radiation Method at BABAR

J.H. Kuhn and A. Santamaria,Tau decays to pions,Z. Phys. C48(1990) 445. [100]BaBarcollaboration,Precise Measurement of thee +e− →π +π−(γ)Cross Section with the Initial-State Radiation Method at BABAR,Phys. Rev. D86(2012) 032013 [1205.2228]

work page internal anchor Pith review Pith/arXiv arXiv 1990
[80]

Plehn, P

T. Plehn, P. Reimitz and P. Richardson,Hadronic Footprint of GeV-Mass Dark Matter, SciPost Phys.8(2020) 092 [1911.11147]. – 36 –

work page arXiv 2020