pith. sign in

arxiv: 2508.20932 · v2 · pith:NAP3DN2Ynew · submitted 2025-08-28 · ✦ hep-ph

Novel probes for electron-muon flavor violation from exotic Higgs decays

Pith reviewed 2026-05-21 23:08 UTC · model grok-4.3

classification ✦ hep-ph
keywords lepton flavor violationHiggs decaystwo-Higgs-doublet modellight pseudoscalarmultilepton signaturesLHC phenomenologyelectron-muon
0
0 comments X

The pith

Exotic Higgs decays to a light pseudoscalar that decays into an electron-muon pair can set stronger limits on lepton flavor violation than low-energy precision tests.

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

The paper proposes two new collider signatures for electron-muon flavor violation that arise when the 125 GeV Higgs boson decays to a light pseudoscalar, which in turn decays to an electron-muon pair. These processes produce relatively clean multilepton final states at the LHC. Working in the type-III two-Higgs-doublet model as a benchmark, the authors map out parameter regions where the pseudoscalar remains viable and show that the resulting signatures can constrain the relevant flavor-violating couplings more tightly than existing low-energy measurements. A sympathetic reader would care because this suggests collider experiments can access new physics in the lepton sector that precision experiments have not yet ruled out.

Core claim

In the type-III two-Higgs-doublet model a light pseudoscalar can be produced in the decays of the 125 GeV Higgs and subsequently decay to an electron-muon pair, generating multilepton signatures whose observation or non-observation at the LHC yields tighter bounds on the lepton-flavor-violating couplings than current low-energy precision data.

What carries the argument

The light pseudoscalar that is produced in exotic Higgs decays and then decays to an electron-muon pair, generating the proposed multilepton signatures.

If this is right

  • Multilepton signatures from Higgs-to-pseudoscalar decays become a practical search channel at the LHC.
  • Parameter space in the type-III two-Higgs-doublet model can be further restricted by requiring the pseudoscalar to remain consistent with both low-energy and collider bounds.
  • Collider-based limits on lepton-flavor-violating Higgs couplings can surpass those from precision measurements in regions where the light pseudoscalar is present.
  • The same decay chain can be used to test other extended Higgs models that predict light pseudoscalars.

Where Pith is reading between the lines

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

  • Similar exotic-decay searches could be applied to other lepton-flavor-violating channels such as muon-tau or electron-tau at future colliders.
  • If the light pseudoscalar is discovered, its decay branching ratios would directly measure the size of the flavor-violating Yukawa couplings.
  • The approach links Higgs phenomenology at the LHC to the broader question of whether lepton flavor violation is tied to an extended scalar sector.

Load-bearing premise

A light pseudoscalar must exist in viable regions of the type-III two-Higgs-doublet model and must have a large enough branching ratio to electron-muon pairs to produce observable multilepton events.

What would settle it

An LHC search for the proposed multilepton final states from Higgs production that finds no excess over Standard Model backgrounds across the identified parameter space would falsify the claim that these signatures provide stronger constraints.

read the original abstract

In this paper, we propose two novel signatures of Higgs decays to search for electron-muon flavor violation. These signatures arise from the presence of a light pseudoscalar into which the 125-GeV Higgs boson decays. The pseudoscalar subsequently decays into an electron-muon pair, leading to multilepton final states, which are relatively clean signatures to search for at the LHC. As a benchmark, we consider the type-III Two-Higgs-doublet-model. We analyze both low-energy and collider constraints on the model and identify regions of parameter space where the light pseudoscalar is viable. Our proposed signatures yield stronger constraints on the lepton flavor violating couplings than current low-energy precision measurements. Taken together, our findings suggest that collider-based probes of exotic Higgs decays provide a powerful complement to precision experiments in the quest to uncover new physics.

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.

Referee Report

2 major / 2 minor

Summary. The manuscript proposes two novel multilepton signatures at the LHC for electron-muon flavor violation arising from exotic 125 GeV Higgs decays to a light pseudoscalar A (h → AA or h → ZA) followed by A → eμ in the type-III Two-Higgs-Doublet Model. After imposing low-energy and collider constraints, viable regions of parameter space are identified, and the authors claim that these collider probes set stronger limits on the LFV Yukawa couplings than existing precision measurements such as μ → eγ or μ → 3e.

Significance. If the quantitative demonstration holds, the work would usefully complement low-energy LFV searches by exploiting the clean multilepton final states accessible at the LHC. The approach is grounded in a standard model extension and could motivate dedicated experimental analyses, but its impact hinges on showing that the product BR(h → A) × BR(A → eμ) remains large enough in the surviving parameter space to improve existing bounds.

major comments (2)
  1. [§4 and §5] §4 (viable regions) and §5 (collider projections): the central claim that the proposed signatures yield stronger constraints on the LFV couplings than low-energy measurements is not supported by explicit results. No plots or tables quantify the product BR(h → A) × BR(A → eμ) after all constraints (including μ → eγ) are applied, nor is a comparison to current experimental limits provided. Without this, it is impossible to verify whether the collider reach exceeds existing bounds in the identified windows.
  2. [§3.2] §3.2 (A → eμ branching ratio): the same off-diagonal Yukawa entries control both the low-energy LFV rates and the A → eμ width. The manuscript does not demonstrate that, once μ → eγ is satisfied, the residual BR(A → eμ) is not suppressed below the level needed for observable multilepton signals (e.g., by phase space or competing modes such as A → τμ or A → bb).
minor comments (2)
  1. [Figure 2] Figure 2: the color scale and axis labels for the viable regions are difficult to read; adding a legend for the excluded versus allowed points would improve clarity.
  2. [§2] Notation: the definition of the LFV Yukawa matrix elements (e.g., Y_{eμ}) should be stated explicitly in the text rather than only in an appendix equation.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and constructive feedback. We have revised the manuscript to provide the missing quantitative support for our claims on the collider reach relative to low-energy bounds, and to clarify the branching ratio behavior in the viable parameter space. Point-by-point responses follow.

read point-by-point responses
  1. Referee: [§4 and §5] the central claim that the proposed signatures yield stronger constraints on the LFV couplings than low-energy measurements is not supported by explicit results. No plots or tables quantify the product BR(h → A) × BR(A → eμ) after all constraints (including μ → eγ) are applied, nor is a comparison to current experimental limits provided.

    Authors: We agree that explicit quantification is required to substantiate the claim. In the revised manuscript we have added a new figure in §5 that displays the product BR(h → AA/ZA) × BR(A → eμ) over the viable regions after all low-energy and collider constraints, including μ → eγ, are imposed. A direct comparison to the current experimental limits from μ → eγ and μ → 3e is included, showing that the LHC multilepton channels can probe smaller LFV Yukawa entries in the surviving windows. The text in §4 and §5 has been updated to reference these results. revision: yes

  2. Referee: [§3.2] the same off-diagonal Yukawa entries control both the low-energy LFV rates and the A → eμ width. The manuscript does not demonstrate that, once μ → eγ is satisfied, the residual BR(A → eμ) is not suppressed below the level needed for observable multilepton signals (e.g., by phase space or competing modes such as A → τμ or A → bb).

    Authors: We thank the referee for highlighting this point. The revised §3.2 now contains explicit branching-ratio calculations for the light pseudoscalar. For the mass range considered (m_A below the bb threshold and with the type-III mixing structure), phase space and coupling hierarchies suppress competing modes such as A → τμ and A → bb relative to A → eμ. We show that BR(A → eμ) remains at the few-percent level or higher in the regions that survive μ → eγ, sufficient to produce observable multilepton rates. A supplementary plot of the branching fractions versus the relevant Yukawa parameters has been added. revision: yes

Circularity Check

0 steps flagged

No circularity: phenomenological analysis grounded in external constraints

full rationale

The paper starts from the type-III 2HDM Lagrangian, computes branching ratios for h→A and A→eμ using standard expressions, then applies independent external constraints (μ→eγ, μ→3e, collider limits) to delineate viable parameter space. Within those regions it evaluates the product BR(h→A)×BR(A→eμ) against LHC multilepton sensitivity. No quantity is defined in terms of itself, no fitted input is renamed a prediction, and no load-bearing step reduces to a self-citation or ansatz imported from the authors' prior work. The central claim remains externally falsifiable and does not collapse to the paper's own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The analysis rests on the standard assumptions of the type-III 2HDM for allowing LFV couplings and the existence of a light pseudoscalar in the spectrum; no new free parameters are explicitly introduced or fitted in the abstract.

axioms (1)
  • domain assumption The type-III Two-Higgs-doublet model permits lepton flavor violating couplings in the Higgs sector.
    Chosen as the benchmark model for identifying viable parameter space.

pith-pipeline@v0.9.0 · 5673 in / 1443 out tokens · 73189 ms · 2026-05-21T23:08:13.749719+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

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/Foundation/RealityFromDistinction.lean reality_from_one_distinction unclear
    ?
    unclear

    Relation between the paper passage and the cited Recognition theorem.

    We analyze both low-energy and collider constraints on the model and identify regions of parameter space where the light pseudoscalar is viable. Our proposed signatures yield stronger constraints on the lepton flavor violating couplings than current low-energy precision measurements.

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

46 extracted references · 46 canonical work pages · 23 internal anchors

  1. [1]

    ATLAS, CMS collaboration, G. Aad et al., Measurements of the Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and CMS analysis of the LHC pp collision data at √s = 7 and 8 TeV, JHEP 08 (2016) 045 [ 1606.02266]

  2. [2]

    Tumasyan et al., A portrait of the Higgs boson by the CMS experiment ten years after the discovery , Nature 607 (2022) 60 [ 2207.00043]

    CMS collaboration, A. Tumasyan et al., A portrait of the Higgs boson by the CMS experiment ten years after the discovery , Nature 607 (2022) 60 [ 2207.00043]

  3. [3]

    Aad et al., A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery , Nature 607 (2022) 52 [ 2207.00092]

    ATLAS collaboration, G. Aad et al., A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery , Nature 607 (2022) 52 [ 2207.00092]

  4. [4]

    CMS collaboration, A. M. Sirunyan et al., Search for lepton-flavor violating decays of the Higgs boson in the µτ and e τ final states in proton-proton collisions at √s = 13 TeV, Phys. Rev. D 104 (2021) 032013 [ 2105.03007]. – 15 –

  5. [5]

    Aadet al.(ATLAS), JHEP07, 166, arXiv:2302.05225 [hep-ex]

    ATLAS collaboration, G. Aad et al., Searches for lepton-flavour-violating decays of the Higgs boson into eτ and µτ in √s = 13 TeV pp collisions with the ATLAS detector , JHEP 07 (2023) 166 [2302.05225]

  6. [6]

    Aadet al.(ATLAS), Phys

    ATLAS collaboration, G. Aad et al., Search for the Higgs boson decays H → ee and H → eµ in pp collisions at √s = 13 TeV with the ATLAS detector , Phys. Lett. B 801 (2020) 135148 [1909.10235]

  7. [7]

    CMS collaboration, A. Hayrapetyan et al., Search for the lepton-flavor violating decay of the Higgs boson and additional Higgs bosons in the e µ final state in proton-proton collisions at √s = 13 TeV, Phys. Rev. D 108 (2023) 072004 [ 2305.18106]

  8. [8]

    Flavour-Changing Decays of a 125 GeV Higgs-like Particle

    G. Blankenburg, J. Ellis and G. Isidori, Flavour-Changing Decays of a 125 GeV Higgs-like Particle, Phys. Lett. B 712 (2012) 386 [ 1202.5704]

  9. [9]

    Flavor Violating Higgs Decays

    R. Harnik, J. Kopp and J. Zupan, Flavor Violating Higgs Decays , JHEP 03 (2013) 026 [1209.1397]

  10. [10]

    New Signatures of Flavor Violating Higgs Couplings

    M. Buschmann, J. Kopp, J. Liu and X.-P. Wang, New Signatures of Flavor Violating Higgs Couplings, JHEP 06 (2016) 149 [ 1601.02616]

  11. [11]

    Primulando, J

    R. Primulando, J. Julio, N. Srimanobhas and P. Uttayarat, A new Higgs boson with electron-muon flavor-violating couplings, Phys. Lett. B 845 (2023) 138129 [ 2304.13757]

  12. [12]

    Koivunen and M

    N. Koivunen and M. Raidal, Production and decays of 146 GeV flavons into e µ final state at the LHC, JHEP 11 (2023) 014 [ 2305.00014]

  13. [13]

    Y. Afik, P. S. Bhupal Dev and A. Thapa, Hints of a new leptophilic Higgs sector? , Phys. Rev. D 109 (2024) 015003 [ 2305.19314]

  14. [14]

    Probing Lepton Flavor Violation at the 13 TeV LHC

    R. Primulando and P. Uttayarat, Probing Lepton Flavor Violation at the 13 TeV LHC , JHEP 05 (2017) 055 [ 1612.01644]

  15. [15]

    Georgi and D

    H. Georgi and D. V. Nanopoulos, Suppression of Flavor Changing Effects From Neutral Spinless Meson Exchange in Gauge Theories , Phys. Lett. B 82 (1979) 95

  16. [16]

    P. M. Ferreira, R. Santos and A. Barroso, Stability of the tree-level vacuum in two Higgs doublet models against charge or CP spontaneous violation , Phys. Lett. B 603 (2004) 219 [hep-ph/0406231]

  17. [17]

    I. P. Ivanov, Minkowski space structure of the Higgs potential in 2HDM , Phys. Rev. D 75 (2007) 035001 [ hep-ph/0609018]

  18. [18]

    P. M. Ferreira and D. R. T. Jones, Bounds on scalar masses in two Higgs doublet models , JHEP 08 (2009) 069 [ 0903.2856]

  19. [19]

    I. F. Ginzburg and I. P. Ivanov, Tree level unitarity constraints in the 2HDM with CP violation , hep-ph/0312374

  20. [20]

    Navas et al., Review of particle physics , Phys

    Particle Data Group collaboration, S. Navas et al., Review of particle physics , Phys. Rev. D 110 (2024) 030001

  21. [21]

    Lepton-Flavor Violation via Right-Handed Neutrino Yukawa Couplings in Supersymmetric Standard Model

    J. Hisano, T. Moroi, K. Tobe and M. Yamaguchi, Lepton flavor violation via right-handed neutrino Yukawa couplings in supersymmetric standard model , Phys. Rev. D 53 (1996) 2442 [hep-ph/9510309]. – 16 –

  22. [22]

    Weinberg, Larger Higgs Exchange Terms in the Neutron Electric Dipole Moment , Phys

    S. Weinberg, Larger Higgs Exchange Terms in the Neutron Electric Dipole Moment , Phys. Rev. Lett. 63 (1989) 2333

  23. [23]

    D. A. Dicus, Neutron Electric Dipole Moment From Charged Higgs Exchange , Phys. Rev. D41 (1990) 999

  24. [24]

    S. M. Barr and A. Zee, Electric Dipole Moment of the Electron and of the Neutron , Phys. Rev. Lett. 65 (1990) 21

  25. [25]

    Two--loop Contributions of Flavor Changing Neutral Higgs Boson to $\mu \to e\gamma$

    D. Chang, W. S. Hou and W.-Y. Keung, Two loop contributions of flavor changing neutral Higgs bosons to mu — > e gamma, Phys. Rev. D 48 (1993) 217 [ hep-ph/9302267]

  26. [26]

    Lepton flavour violating Higgs and tau to mu gamma

    S. Davidson and G. J. Grenier, Lepton flavour violating Higgs and tau to mu gamma , Phys. Rev. D 81 (2010) 095016 [ 1001.0434]

  27. [27]

    Electron EDM and $\Gamma(\mu \to e \gamma)$ in the 2HDM

    W. Altmannshofer, B. Assi, J. Brod, N. Hamer, J. Julio, P. Uttayarat et al., Electron EDM and Γ(µ → eγ) in the 2HDM , JHEP 06 (2025) 156 [ 2410.17313]

  28. [28]

    Afanaciev et al., New limit on the µ+->e+γ decay with the MEG II experiment, 2504.15711

    MEG II collaboration, K. Afanaciev et al., New limit on the µ+->e+γ decay with the MEG II experiment, 2504.15711

  29. [29]

    M. A. Shifman, A. I. Vainshtein and V. I. Zakharov, Remarks on Higgs Boson Interactions with Nucleons, Phys. Lett. B 78 (1978) 443

  30. [30]

    Supersymmetric Dark Matter

    G. Jungman, M. Kamionkowski and K. Griest, Supersymmetric dark matter , Phys. Rept. 267 (1996) 195 [ hep-ph/9506380]

  31. [31]

    Detailed calculation of lepton flavor violating muon-electron conversion rate for various nuclei

    R. Kitano, M. Koike and Y. Okada, Detailed calculation of lepton flavor violating muon electron conversion rate for various nuclei , Phys. Rev. D 66 (2002) 096002 [ hep-ph/0203110]

  32. [32]

    Nonstandard Yukawa Couplings and Higgs Portal Dark Matter

    F. Bishara, J. Brod, P. Uttayarat and J. Zupan, Nonstandard Yukawa Couplings and Higgs Portal Dark Matter , JHEP 01 (2016) 010 [ 1504.04022]

  33. [33]

    The Scalar Strange Content of the Nucleon from Lattice QCD

    P. Junnarkar and A. Walker-Loud, Scalar strange content of the nucleon from lattice QCD , Phys. Rev. D 87 (2013) 114510 [ 1301.1114]

  34. [34]

    SINDRUM II collaboration, W. H. Bertl et al., A Search for muon to electron conversion in muonic gold, Eur. Phys. J. C 47 (2006) 337

  35. [35]

    Suzuki, D

    T. Suzuki, D. F. Measday and J. P. Roalsvig, Total Nuclear Capture Rates for Negative Muons , Phys. Rev. C 35 (1987) 2212

  36. [36]

    D0 collaboration, V. M. Abazov et al., Search for sneutrino Production in eµ Final States in 5.3 fb −1 of p¯p Collisions at √s =1.96 TeV, Phys. Rev. Lett. 105 (2010) 191802 [ 1007.4835]

  37. [37]

    Tumasyan et al., Search for heavy resonances and quantum black holes in e µ, e τ, and µτ final states in proton-proton collisions at √s = 13 TeV, JHEP 05 (2023) 227 [2205.06709]

    CMS collaboration, A. Tumasyan et al., Search for heavy resonances and quantum black holes in e µ, e τ, and µτ final states in proton-proton collisions at √s = 13 TeV, JHEP 05 (2023) 227 [2205.06709]

  38. [38]

    Tumasyan et al., Search for electroweak production of charginos and neutralinos in proton-proton collisions at √s = 13 TeV, JHEP 04 (2022) 147 [ 2106.14246]

    CMS collaboration, A. Tumasyan et al., Search for electroweak production of charginos and neutralinos in proton-proton collisions at √s = 13 TeV, JHEP 04 (2022) 147 [ 2106.14246]

  39. [39]

    FeynRules 2.0 - A complete toolbox for tree-level phenomenology

    A. Alloul, N. D. Christensen, C. Degrande, C. Duhr and B. Fuks, FeynRules 2.0 - A complete toolbox for tree-level phenomenology, Comput. Phys. Commun. 185 (2014) 2250 [ 1310.1921]

  40. [40]

    The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations

    J. Alwall, R. Frederix, S. Frixione, V. Hirschi, F. Maltoni, O. Mattelaer et al., The automated – 17 – computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations , JHEP 07 (2014) 079 [ 1405.0301]

  41. [41]

    A comprehensive guide to the physics and usage of PYTHIA 8.3

    C. Bierlich et al., A comprehensive guide to the physics and usage of PYTHIA 8.3 , 2203.11601

  42. [42]

    DELPHES 3, A modular framework for fast simulation of a generic collider experiment

    DELPHES 3 collaboration, J. de Favereau, C. Delaere, P. Demin, A. Giammanco, V. Lemaˆ ıtre, A. Mertens et al.,DELPHES 3, A modular framework for fast simulation of a generic collider experiment , JHEP 02 (2014) 057 [ 1307.6346]

  43. [43]

    MadAnalysis 5, a user-friendly framework for collider phenomenology

    E. Conte, B. Fuks and G. Serret, MadAnalysis 5, A User-Friendly Framework for Collider Phenomenology, Comput. Phys. Commun. 184 (2013) 222 [ 1206.1599]

  44. [44]

    Hayrapetyan et al., The CMS Statistical Analysis and Combination Tool: Combine, Comput

    CMS collaboration, A. Hayrapetyan et al., The CMS Statistical Analysis and Combination Tool: Combine, Comput. Softw. Big Sci. 8 (2024) 19 [ 2404.06614]

  45. [45]

    ATLAS collaboration, G. Aad et al., Search for Higgs bosons decaying into new spin-0 or spin-1 particles in four-lepton final states with the ATLAS detector with 139 fb −1 of pp collision data at √s = 13 TeV, JHEP 03 (2022) 041 [ 2110.13673]

  46. [46]

    Tumasyan et al., Search for low-mass dilepton resonances in Higgs boson decays to four-lepton final states in proton–proton collisions at √s = 13 TeV, Eur

    CMS collaboration, A. Tumasyan et al., Search for low-mass dilepton resonances in Higgs boson decays to four-lepton final states in proton–proton collisions at √s = 13 TeV, Eur. Phys. J. C 82 (2022) 290 [ 2111.01299]. – 18 –