REVIEW 4 major objections 5 minor 1 cited by
High-energy cLFV at $\mu$TRISTAN: HNL extensions of the Standard Model
T0 review · 4 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read The paper argues that muTRISTAN could discover HNL-induced charged lepton flavour violation in e-mu scattering, with tau-flavour channels beating FCC-ee and low-energy probes by orders of magnitude.
desk verdict A careful, genuinely new one-loop computation of HNL-induced cLFV at muTRISTAN; the cross-sections are the contribution, while the 'orders of magnitude' sensitivity claim outruns the paper's own cut-and-count caveats. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the complete one-loop amplitude for $\mu^+e^- \to \ell_\alpha^+\ell_\beta^-$ in the limit of massless external fermions, written after Fierz rearrangement in terms of three chiral amplitudes $A_{LL}$, $A_{LR}$ and $A_{RL}$ that combine photon- and $Z$-penguin form factors $F_\gamma^{\alpha\beta}(q^2)$ and $F_Z^{\alpha\beta}(q^2)$ with four box-diagram functions $F_1$ and $F_2$; all flavour violation enters through the extended leptonic mixing matrix $U$. From these amplitudes the authors derive the differential cross section, the pseudo-rapidity distributions $d\sigma/d\eta$ and the forward-backward asymmetry $A_{FB}$. This machinery carries the argument because it connects the high-energy scattering rates to the same form factors that control low-energy cLFV decays and $Z\to\ell_\alpha\ell_\beta$, and it allows the angular cuts ($|\eta|\leq 4$, $2\leq \eta_\ell \leq 4$) that reduce the SM background to sub-event levels.
What would settle it
A detector-level Monte Carlo of $\mu^+e^-$ collisions at $\sqrt{s}=346.4$ GeV that includes $\tau$ fakes from $\mu^+e^- \to \mu^+e^-$, in-flight muon decays and beam backgrounds would settle the projection: if the background in the signal region with missing transverse energy $\leq 10$ GeV and lepton rapidities $2 \leq \eta \leq 4$ exceeds roughly 10 events at $1~\mathrm{ab}^{-1}$, or if the signal efficiency falls below about 0.1%, the claimed $e\tau$/$\mu\tau$ sensitivity contours in the $(M_R,\mu_X)$ plane would weaken and the quoted advantage over FCC-ee would not hold.
Extended reading notes
Core claim
In the paper's own terms, HNLs with non-negligible mixings to active neutrinos generate cLFV at one loop, and this is enough to make $\mu^+e^- \to \ell_\alpha^+\ell_\beta^-$ scattering observable at $\mu$TRISTAN. The central quantitative claim is that, in both a minimal ad-hoc extension with two sterile states and in the Inverse Seesaw ISS(3,3), the cross sections for $\mu^+e^- \to \tau^+e^-$ and $\mu^+e^- \to \mu^+\tau^-$ remain large over a wide range of HNL masses (roughly $100$ GeV to several TeV), so that even with a deliberately conservative detector efficiency of order 1% the expected event counts reach the thousands. In the $(M_R,\mu_X)$ plane of the ISS(3,3), the resulting sensitivity contours for $e\tau$ and $\mu\tau$ flavour violation lie several orders of magnitude beyond the future sensitivities of searches for $\tau\to \ell\gamma$, $\tau\to 3\ell$ and $Z\to \ell\tau$, while for $\mu e$ flavour violation low-energy dedicated experiments remain superior. The paper further claims that the forward-backward asymmetry of the final-state leptons is sensitive to which amplitude topology dominates and to CP-violating phases of the generalised lepton mixing matrix.
Load-bearing premise
The reach projections depend on the assumption that a basic cut-and-count selection leaves the SM background below one event per $ab^{-1}$ while keeping a total signal efficiency of about 1%, and that ten signal events then constitute a discovery-level sensitivity.
Editorial extensions
If this is right
- For $e\tau$ and $\mu\tau$ flavour pairs, $\mu$TRISTAN would probe HNL parameter space in the ISS(3,3) several orders of magnitude deeper than future $\tau\to \ell\gamma$, $\tau\to 3\ell$ and $Z\to\ell\tau$ searches, making it a discovery machine for tau-flavoured cLFV.
- For $\mu e$ flavour violation, low-energy experiments such as $\mu\to e$ conversion remain more sensitive, so $\mu$TRISTAN and dedicated high-intensity facilities are complementary rather than competing.
- A measurement of $A_{FB}$ for $\mu^+e^- \to e^+e^-$ and $\mu^+e^- \to \mu^+\mu^-$ could distinguish $s$-channel from $t$-channel (or box) dominance and give information on the HNL mass scale.
- Even if no low-energy cLFV decay or $Z$-pole signal is ever seen, $\mu$TRISTAN could still observe $\tau$-flavoured cLFV events in large regions of the allowed parameter space.
Reading between the lines
- If real detector performance gives a signal efficiency below the assumed 1% or a non-negligible background from $\tau$ fakes in $\mu^+e^- \to \mu^+e^-$, the sensitivity contours in the $(M_R,\mu_X)$ plane would shift; the 'orders of magnitude' statements should be read as contingent on the background and efficiency model.
- The same form-factor calculation could be extended to $\mu^+e^- \to q\bar q$, which would connect high-energy cLFV to the $\mu$-$e$ conversion process that currently gives the strongest low-energy bounds; the authors mention this as future work.
- The strong dependence of $A_{FB}$ on the CP phase $\delta_{24}$ suggests that angular observables at lepton colliders could serve as CP-violation probes in the sterile-neutrino sector, an application the paper does not develop.
- Because the comparison with FCC-ee is driven by irreducible $\tau$ misidentification at the $Z$ pole, the real $\tau$-tagging performance at $\mu$TRISTAN will decide whether the claimed advantage survives; the underlying cross-section advantage alone does not guarantee it.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper computes the one-loop amplitudes, cross-sections, and angular observables for charged lepton flavour violating (cLFV) processes μ+ e− → ℓ+α ℓ−β in Standard Model extensions with heavy neutral leptons (HNLs), considering both a minimal '3+2' ad-hoc model and the ISS(3,3) inverse seesaw realisation. It then uses these results to project the sensitivity of a future μTRISTAN collider and compares it with low-energy cLFV searches and with cLFV Z-pole searches at FCC-ee. The central claim is that, while μ−e flavour violation remains best probed at low energies, eτ and μτ flavour violation searches at μTRISTAN could exceed the prospects of low-energy tau decays and of FCC-ee by several orders of magnitude.
Significance. If the sensitivity projection were reliable, this paper would make a strong case for μTRISTAN as a discovery machine for tau-flavour-violating cLFV in HNL models, with reach far beyond other planned facilities. The analytic part of the work is its main strength: the loop amplitudes are presented in detail, the Fierz and Dirac identities used in the reduction are spelled out in the appendices, the question of gauge invariance of the off-shell Z-penguin contributions is discussed, and the ISS(3,3) implementation is anchored to neutrino oscillation data through the Casas-Ibarra parametrisation. These parts are a useful reference that is largely independent of the collider projection. The sensitivity analysis, however, is currently not at the same standard, and the 'orders of magnitude' claim rests on assumptions that are not yet quantitatively justified.
major comments (4)
- [Sec. 5.2, Eq. (58), Figs. 12-13] The projected sensitivity contours are derived from a cut-and-count estimate based on a single leading-order background process, μ+e−→τ+e−νν with σ≈21 fb, reduced to 6×10−4 fb by the cuts, and on a global 1% signal efficiency obtained from a 25% cut efficiency, a 40% tau-tagging efficiency, and an additional ad-hoc suppression factor. No detector simulation, no tau-decay Monte Carlo, no estimate of tau fakes from μ+e−→μ+e−, no beam-induced background, and no tau misidentification rate are provided. Because the headline 'several orders of magnitude' claim derives directly from these contours, this is a load-bearing part of the paper and needs substantially stronger support.
- [Sec. 5.2] The signal process itself contains a tau lepton, whose decay necessarily produces missing neutrinos, but the manuscript does not state how the /ET≤10 GeV cut is applied to signal events. If tau decays are not simulated, the quoted 25% signal efficiency after the basic cuts is not justified, and a significant fraction of signal events could fail the missing-energy cut. This would shift the sensitivity contours in Figs. 12 and 13 upward and could materially weaken the comparison with FCC-ee and low-energy tau probes. The authors should either include tau decays explicitly in the efficiency estimate or restrict the sensitivity claims accordingly.
- [Sec. 5.2] The 40% tau-tagging efficiency is taken from an ATLAS high-mass resonance search, while the signal leptons are required to lie in the range 2.0≤ηℓ≤4.0. ATLAS tau identification is not established at such forward pseudorapidities, and a muTRISTAN-specific detector does not yet exist. A scan over plausible tau-tagging efficiencies, or a clear statement of the geometric and kinematic assumptions, is needed before the contours are used for quantitative sensitivity comparisons.
- [Sec. 6 and Fig. 13] The claim that μTRISTAN is more sensitive to μ−τ flavour violation than FCC-ee even with 5×10^12 Z bosons is based on an 'irreducible systematic misidentification' of secondary leptons in Z→ττ, but no quantitative estimate of that systematic floor is given. The FCC-ee sensitivities quoted in Table 2 may already include detector assumptions, so without a concrete comparison at the same level of detail the stated outperformance by 'several orders of magnitude' is not established.
minor comments (5)
- [Eq. (58)] The printed expression 'S = S√S+B' should presumably read S=S/√(S+B); as typeset it is not a valid formula.
- [Figs. 12-13] The captions of Figs. 12 and 13 do not state the centre-of-mass energy used for the μTRISTAN cross-sections; the text should specify whether √s=346.4 GeV or another configuration is assumed.
- [Sec. 5.1, Eq. (51)] The benchmark in Eq. (51) is a single point in the ad-hoc parameter space; the text should state more explicitly how the conclusions depend on the choice s34=s35=0.1 and on the degenerate-mass assumption.
- [Sec. 5.1 and Fig. 10] The comparison in Fig. 10 refers to 'events' without specifying the tau decay channel; since signal and background rates are quoted in fb, the reader should be told whether tau decays are part of the event definition or not.
- [Sec. 3 and Sec. 5.1] The use of 'ATLAS-like rapidity coverage |η|≤4' for the signal integration is a useful illustration, but the muTRISTAN detector has not been designed; a brief comment on how this choice affects the quoted cross-sections would improve the presentation.
Circularity Check
No significant circularity: the HNL benchmark parameters are a priori inputs, the ISS Yukawas are fixed by neutrino data, and the muTRISTAN sensitivity projection uses an explicit, un-fitted counting model.
full rationale
The paper's central derivation is self-contained. The scattering cross-sections and angular observables are computed analytically from the extended lepton mixing matrix and loop functions (Eqs. 5-39), with no target observable fitted. In the ad-hoc '3+2' model, the benchmark mixing angles in Eq. (51) are chosen by hand before any observable is computed; in the ISS(3,3) study, the Yukawa couplings are fixed by neutrino oscillation data through the modified Casas-Ibarra parametrization of Eq. (44), not by any muTRISTAN result. The low-energy cLFV rates and the high-energy cross-sections are independent functions of the same model parameters, so comparing their projected sensitivities is a legitimate model-level comparison, not a prediction equivalent to its input. The 'sensitivity' prescription of Sec. 5.2 (Eq. 58) is an assumed detector model: a 1% total signal efficiency, 10 signal events, and negligible background. These numbers are not derived from the cross-sections or from any fitted parameter, so the projection is not circular, although it is admittedly optimistic and fragile. The paper explicitly acknowledges that 'in the absence of concrete detector designs, a full study of possible backgrounds and systematics is clearly beyond the scope of this work.' The self-citations present in the manuscript ([66] for the finiteness of the Z-penguin, [84] for lepton flavour universality observables, and [71] for CPV phases) are technical references and do not carry the paper's central claim: the muTRISTAN reach and the comparison with FCC-ee and low-energy tau probes rest on the analytic cross-section computation and the explicit counting prescription, not on an unverified self-citation chain. No circular step satisfying the definitional or fitted-input patterns was found.
Assumptions & free parameters
free parameters (6)
- ad-hoc benchmark mixing angles =
s14=s15=5e-4, s24=s25=0.01, s34=s35=0.1
- HNL masses m4=m5 =
0.1, 0.5, 1, 5 TeV
- signal efficiency =
1%
- minimum required signal events =
10
- ISS(3,3) parameters MR, mu_X =
MR in [100, 10^4] GeV, mu_X in [10^-10, 10^-4] GeV
- lightest neutrino mass m0 =
10^-5 eV
assumptions (6)
- domain assumption Leptonic mixing matrix U is (semi-)unitary; the would-be PMNS is non-unitary due to HNL mixing.
- domain assumption External fermions are massless in the one-loop computation.
- standard math SM gauge structure and Feynman rules extended with HNL vertices.
- domain assumption The ad-hoc '3+2' model is a valid effective description with no mechanism for neutrino mass.
- ad hoc to paper Casas-Ibarra parametrization with R=1 and degenerate MR reproduces neutrino oscillation data.
- domain assumption Perturbative unitarity bound Gamma(Ni)/m_Ni < 1/2.
Cite this review
Pith. "Pith review of High-energy cLFV at $\mu$TRISTAN: HNL extensions of the Standard Model." pith.science (2026). https://pith.science/paper/RLUEOYFO
@misc{pith2026241204331,
author = {Pith},
title = {Pith review of: High-energy cLFV at $\mu$TRISTAN: HNL extensions of the Standard Model},
year = {2026},
howpublished = {\url{https://pith.science/paper/RLUEOYFO}},
note = {Machine review of arXiv:2412.04331}
}
abstract
Within the context of heavy neutral lepton (HNL) extensions of the Standard Model, we compute the cross-sections for $\mu^+ e^-\to \ell_\alpha^+\ell_\beta^-$ scattering, as well as several angular observables. In particular, we investigate the future sensitivity of a $\mu$TRISTAN collider in discovering such charged lepton flavour violating processes and the potential constraining power of these searches on the parameter space of HNL models. Our results show that while low-energy probes of $\mu-e$ flavour violation do offer the most promising potential, the prospects for $e\tau$ and $\mu\tau$ flavour violation searches at $\mu$TRISTAN can exceed those of related low-energy probes (as well as flavour violating $Z$-pole processes at FCC-ee) by several orders of magnitude.
Figures
Figures from the paper (10 more)
Forward citations
Cited by 1 Pith paper
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Taming flavour violation in the Inverse Seesaw
New eta-based parametrisations of the ISS(3,3) show that Z-penguin flavour violation can reveal non-degenerate heavy sterile mixing even when radiative decays are absent.
Reference graph
Works this paper leans on
-
[1]
Minkowski, µ → eγ at a Rate of One Out of 109 Muon Decays?, Phys
P. Minkowski, µ → eγ at a Rate of One Out of 109 Muon Decays?, Phys. Lett. B 67 (1977) 421
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
1979
-
[3]
Glashow, The Future of Elementary Particle Physics , NATO Sci
S.L. Glashow, The Future of Elementary Particle Physics , NATO Sci. Ser. B 61 (1980) 687
1980
-
[4]
M. Gell-Mann, P. Ramond and R. Slansky, Complex Spinors and Unified Theories , Conf. Proc. C 790927 (1979) 315 [ 1306.4669]
arXiv 1979
-
[5]
Mohapatra and G
R.N. Mohapatra and G. Senjanovic, Neutrino Mass and Spontaneous Parity Nonconservation , Phys. Rev. Lett. 44 (1980) 912
1980
-
[6]
E.K. Akhmedov, M. Lindner, E. Schnapka and J.W.F. Valle, Dynamical left-right symmetry breaking , Phys. Rev. D 53 (1996) 2752 [ hep-ph/9509255]
arXiv 1996
-
[7]
Barr, A Different seesaw formula for neutrino masses , Phys
S.M. Barr, A Different seesaw formula for neutrino masses , Phys. Rev. Lett. 92 (2004) 101601 [hep-ph/0309152]
arXiv 2004
-
[8]
M. Malinsky, J.C. Romao and J.W.F. Valle, Novel supersymmetric SO(10) seesaw mechanism , Phys. Rev. Lett. 95 (2005) 161801 [ hep-ph/0506296]
arXiv 2005
Show all 118 references
-
[9]
Schechter and J.W.F
J. Schechter and J.W.F. Valle, Neutrino Masses in SU(2) x U(1) Theories , Phys. Rev. D 22 (1980) 2227
1980
-
[10]
Gronau, C.N
M. Gronau, C.N. Leung and J.L. Rosner, Extending Limits on Neutral Heavy Leptons , Phys. Rev. D 29 (1984) 2539
1984
-
[11]
Mohapatra and J.W.F
R.N. Mohapatra and J.W.F. Valle, Neutrino Mass and Baryon Number Nonconservation in Superstring Models, Phys. Rev. D 34 (1986) 1642
1986
-
[12]
Riemann and G
T. Riemann and G. Mann, NONDIAGONAL Z DECAY: Z — > E MU , in 10th International Conference on Neutrino Physics: Neutrino ’82 , pp. 58–61, 1982
1982
-
[13]
Illana, M
J.I. Illana, M. Jack and T. Riemann, Predictions for Z — > mu tau and related reactions , hep-ph/0001273
-
[14]
Mann and T
G. Mann and T. Riemann, EFFECTIVE FLA VOR CHANGING WEAK NEUTRAL CURRENT IN THE STANDARD THEORY AND Z BOSON DECAY , Annalen Phys. 40 (1984) 334
1984
-
[15]
Illana and T
J.I. Illana and T. Riemann, Charged lepton flavor violation from massive neutrinos in Z decays , Phys. Rev. D 63 (2001) 053004 [ hep-ph/0010193]
2001 arXiv
-
[16]
Alonso, M
R. Alonso, M. Dhen, M.B. Gavela and T. Hambye, Muon conversion to electron in nuclei in type-I seesaw models, JHEP 01 (2013) 118 [ 1209.2679]
2013 arXiv
-
[17]
Ilakovac and A
A. Ilakovac and A. Pilaftsis, Flavor violating charged lepton decays in seesaw-type models , Nucl. Phys. B 437 (1995) 491 [ hep-ph/9403398]
1995 arXiv
-
[18]
Ma and A
E. Ma and A. Pramudita, Flavor Changing Effective Neutral Current Couplings in the Weinberg-Salam Model, Phys. Rev. D 22 (1980) 214
1980
-
[19]
Deppisch and J.W.F
F. Deppisch and J.W.F. Valle, Enhanced lepton flavor violation in the supersymmetric inverse seesaw model, Phys. Rev. D 72 (2005) 036001 [ hep-ph/0406040]
2005 arXiv
-
[20]
Deppisch, T.S
F. Deppisch, T.S. Kosmas and J.W.F. Valle, Enhanced mu- - e- conversion in nuclei in the inverse seesaw model, Nucl. Phys. B 752 (2006) 80 [ hep-ph/0512360]
2006 arXiv
-
[21]
D.N. Dinh, A. Ibarra, E. Molinaro and S.T. Petcov, The µ − e Conversion in Nuclei, µ → eγ, µ→ 3e Decays and TeV Scale See-Saw Scenarios of Neutrino Mass Generation , JHEP 08 (2012) 125 [1205.4671]
2012 arXiv
-
[22]
Hambye, CLFV and the origin of neutrino masses , Nucl
T. Hambye, CLFV and the origin of neutrino masses , Nucl. Phys. B Proc. Suppl. 248-250 (2014) 13 [1312.5214]
2014 arXiv
-
[23]
Abada, M.E
A. Abada, M.E. Krauss, W. Porod, F. Staub, A. Vicente and C. Weiland, Lepton flavor violation in low-scale seesaw models: SUSY and non-SUSY contributions , JHEP 11 (2014) 048 [ 1408.0138]
2014 arXiv
-
[24]
Abada, V
A. Abada, V. De Romeri and A.M. Teixeira, Impact of sterile neutrinos on nuclear-assisted cLFV processes, JHEP 02 (2016) 083 [ 1510.06657]
2016 arXiv
-
[25]
Abada, D
A. Abada, D. Beˇ cirevi´ c, M. Lucente and O. Sumensari,Lepton flavor violating decays of vector quarkonia and of the Z boson, Phys. Rev. D 91 (2015) 113013 [ 1503.04159]. 27
2015 arXiv
-
[26]
Abada, V
A. Abada, V. De Romeri, J. Orloff and A.M. Teixeira, In-flight cLFV conversion: e − µ , e − τ and µ − τ in minimal extensions of the standard model with sterile fermions , Eur. Phys. J. C 77 (2017) 304 [1612.05548]
2017 arXiv
-
[27]
Calibbi and G
L. Calibbi and G. Signorelli, Charged Lepton Flavour Violation: An Experimental and Theoretical Introduction, Riv. Nuovo Cim. 41 (2018) 71 [ 1709.00294]
2018 arXiv
-
[28]
Abada and A.M
A. Abada and A.M. Teixeira, Heavy neutral leptons and high-intensity observables , Front. in Phys. 6 (2018) 142 [ 1812.08062]
2018 arXiv
-
[29]
Arganda, M.J
E. Arganda, M.J. Herrero, X. Marcano and C. Weiland, Imprints of massive inverse seesaw model neutrinos in lepton flavor violating Higgs boson decays , Phys. Rev. D 91 (2015) 015001 [ 1405.4300]
2015 arXiv
-
[30]
Marcano and R.A
X. Marcano and R.A. Morales, Flavor techniques for LFV processes: Higgs decays in a general seesaw model, Front. in Phys. 7 (2020) 228 [ 1909.05888]
2020 arXiv
-
[31]
Urqu ´ ıa-Calder´ on, I
K.A. Urqu ´ ıa-Calder´ on, I. Timiryasov and O. Ruchayskiy,Heavy neutral leptons — Advancing into the PeV domain , JHEP 08 (2023) 167 [ 2206.04540]
2023 arXiv
-
[32]
FCC-ee study Teamcollaboration, Search for Heavy Right Handed Neutrinos at the FCC-ee , Nucl. Part. Phys. Proc. 273-275 (2016) 1883 [ 1411.5230]
2016 arXiv
-
[33]
Antusch, E
S. Antusch, E. Cazzato and O. Fischer, Sterile neutrino searches at future e−e+, pp, and e−p colliders, Int. J. Mod. Phys. A 32 (2017) 1750078 [ 1612.02728]
2017 arXiv
-
[34]
Y. Cai, T. Han, T. Li and R. Ruiz, Lepton Number Violation: Seesaw Models and Their Collider Tests , Front. in Phys. 6 (2018) 40 [ 1711.02180]
2018 arXiv
-
[35]
Blondel et al., Searches for long-lived particles at the future FCC-ee , Front
A. Blondel et al., Searches for long-lived particles at the future FCC-ee , Front. in Phys. 10 (2022) 967881 [2203.05502]
2022 arXiv
-
[36]
Abdullahi et al., The present and future status of heavy neutral leptons , J
A.M. Abdullahi et al., The present and future status of heavy neutral leptons , J. Phys. G 50 (2023) 020501 [2203.08039]
2023 arXiv
-
[37]
Abada, P
A. Abada, P. Escribano, X. Marcano and G. Piazza, Collider searches for heavy neutral leptons: beyond simplified scenarios, Eur. Phys. J. C 82 (2022) 1030 [ 2208.13882]
2022 arXiv
-
[38]
Giffin, S
P. Giffin, S. Gori, Y.-D. Tsai and D. Tuckler, Heavy neutral leptons at beam dump experiments of future lepton colliders , JHEP 04 (2023) 046 [ 2206.13745]
2023 arXiv
-
[39]
Drewes, Distinguishing Dirac and Majorana Heavy Neutrinos at Lepton Colliders , PoS ICHEP2022 (2022) 608 [ 2210.17110]
M. Drewes, Distinguishing Dirac and Majorana Heavy Neutrinos at Lepton Colliders , PoS ICHEP2022 (2022) 608 [ 2210.17110]
2022 arXiv
-
[40]
Ovchynnikov and J.-Y
M. Ovchynnikov and J.-Y. Zhu, Search for the dipole portal of heavy neutral leptons at future colliders , JHEP 07 (2023) 039 [ 2301.08592]
2023 arXiv
-
[41]
Ajmal, P
S. Ajmal, P. Azzi, S. Giappichini, M. Klute, O. Panella, M. Presilla et al., Searching for type I seesaw mechanism in a two Heavy Neutral Leptons scenario at FCC-ee , 2410.03615
-
[42]
Antusch, J
S. Antusch, J. Hajer and B.M.S. Oliveira, Discovering heavy neutrino-antineutrino oscillations at the Z-pole, JHEP 11 (2024) 102 [ 2408.01389]
2024
-
[43]
Chakraborty, H
I. Chakraborty, H. Roy and T. Srivastava, Searches for heavy neutrinos at multi-TeV muon collider: a resonant leptogenesis perspective, Eur. Phys. J. C 83 (2023) 280 [ 2206.07037]
2023 arXiv
-
[44]
M¸ eka la, J
K. M¸ eka la, J. Reuter and A.F.˙Zarnecki, Optimal search reach for heavy neutral leptons at a muon collider, Phys. Lett. B 841 (2023) 137945 [ 2301.02602]
2023 arXiv
-
[45]
T.H. Kwok, L. Li, T. Liu and A. Rock, Searching for heavy neutral leptons at a future muon collider , Phys. Rev. D 110 (2024) 075009 [ 2301.05177]
2024 arXiv
-
[46]
P. Li, Z. Liu and K.-F. Lyu, Heavy neutral leptons at muon colliders , JHEP 03 (2023) 231 [2301.07117]
2023 arXiv
-
[47]
Mikulenko and M
O. Mikulenko and M. Marinichenko, Measuring lepton number violation in heavy neutral lepton decays at the future muon collider , JHEP 01 (2024) 032 [ 2309.16837]
2024 arXiv
-
[48]
Urqu ´ ıa-Calder´ on,Long-lived heavy neutral leptons at lepton colliders as a probe of left-right-symmetric models, Phys
K.A. Urqu ´ ıa-Calder´ on,Long-lived heavy neutral leptons at lepton colliders as a probe of left-right-symmetric models, Phys. Rev. D 109 (2024) 055002 [ 2310.17406]
2024 arXiv
-
[49]
de Lima, D
C.H. de Lima, D. McKeen, J.N. Ng, M. Shamma and D. Tuckler, Probing Lepton Number Violation at Same-Sign Lepton Colliders , 2411.15303
-
[50]
Marcos, A
M.B. Marcos, A. de Giorgi, L. Merlo and J.-L. Tastet, ALPs and HNLs at LHC and Muon Colliders: Uncovering New Couplings and Signals , 2407.14970. 28
-
[51]
Hamada, R
Y. Hamada, R. Kitano, R. Matsudo, H. Takaura and M. Yoshida, µTRISTAN, PTEP 2022 (2022) 053B02 [2201.06664]
2022 arXiv
-
[52]
M. Lu, A.M. Levin, C. Li, A. Agapitos, Q. Li, F. Meng et al., The physics case for an electron-muon collider, Adv. High Energy Phys. 2021 (2021) 6693618 [ 2010.15144]
2021 arXiv
-
[53]
Bossi and P
F. Bossi and P. Ciafaloni, Lepton Flavor Violation at muon-electron colliders , JHEP 10 (2020) 033 [2003.03997]
2020 arXiv
-
[54]
Kriewald, J
J. Kriewald, J. Orloff, E. Pinsard and A.M. Teixeira, Prospects for a flavour violating Z ′ explanation of ∆aµ,e, Eur. Phys. J. C 82 (2022) 844 [ 2204.13134]
2022 arXiv
-
[55]
Goudelis, J
A. Goudelis, J. Kriewald, E. Pinsard and A.M. Teixeira, cLFV leptophilic Z ′ as a dark matter portal: prospects for colliders, Eur. Phys. J. C 84 (2024) 804 [ 2312.14103]
2024 arXiv
-
[56]
P.S.B. Dev, J. Heeck and A. Thapa, Neutrino mass models at µTRISTAN, Eur. Phys. J. C 84 (2024) 148 [2309.06463]
2024 arXiv
-
[57]
Bolton, J
P.D. Bolton, J. Kriewald, M. Nemevˇ sek, F. Nesti and J.C. Vasquez, On Lepton Number Violation in the Type II Seesaw, 2408.00833
-
[58]
A. Das, J. Li, S. Mandal, T. Nomura and R. Zhang, Testing tree level TeV scale tyep-I and type-II seesaw scenarios in µTRISTAN, 2410.21956
-
[59]
Kondo et al., Re-Acceleration of Ultra Cold Muon in J-PARC Muon Facility , in 9th International Particle Accelerator Conference, 6, 2018, DOI
Y. Kondo et al., Re-Acceleration of Ultra Cold Muon in J-PARC Muon Facility , in 9th International Particle Accelerator Conference, 6, 2018, DOI
2018
-
[60]
Abe et al., A New Approach for Measuring the Muon Anomalous Magnetic Moment and Electric Dipole Moment, PTEP 2019 (2019) 053C02 [ 1901.03047]
M. Abe et al., A New Approach for Measuring the Muon Anomalous Magnetic Moment and Electric Dipole Moment, PTEP 2019 (2019) 053C02 [ 1901.03047]
2019 arXiv
-
[61]
Adolphsen et al., eds., The International Linear Collider Technical Design Report - Volume 3.I: Accelerator \& in the Technical Design Phase , 1306.6353
C. Adolphsen et al., eds., The International Linear Collider Technical Design Report - Volume 3.I: Accelerator \& in the Technical Design Phase , 1306.6353
-
[62]
FCC collaboration, FCC-ee: The Lepton Collider: Future Circular Collider Conceptual Design Report Volume 2, Eur. Phys. J. ST 228 (2019) 261
2019
-
[63]
CEPC Study Groupcollaboration, CEPC Conceptual Design Report: Volume 1 - Accelerator , 1809.00285
-
[64]
Hamada, R
Y. Hamada, R. Kitano, R. Matsudo and H. Takaura, Precision µ+µ+ and µ+e− elastic scatterings, PTEP 2023 (2023) 013B07 [ 2210.11083]
2023 arXiv
-
[65]
Hahn and M
T. Hahn and M. Perez-Victoria, Automatized one loop calculations in four-dimensions and D-dimensions, Comput. Phys. Commun. 118 (1999) 153 [ hep-ph/9807565]
1999 arXiv
-
[67]
Brod and M
J. Brod and M. Gorbahn, The Z Penguin in Generic Extensions of the Standard Model , JHEP 09 (2019) 027 [ 1903.05116]
2019 arXiv
-
[68]
Denner, H
A. Denner, H. Eck, O. Hahn and J. Kublbeck, Feynman rules for fermion number violating interactions , Nucl. Phys. B 387 (1992) 467
1992
-
[69]
Nieves and P.B
J.F. Nieves and P.B. Pal, Generalized Fierz identities , Am. J. Phys. 72 (2004) 1100 [ hep-ph/0306087]
2004 arXiv
-
[70]
Abada and T
A. Abada and T. Toma, Electric Dipole Moments of Charged Leptons with Sterile Fermions , JHEP 02 (2016) 174 [ 1511.03265]
2016 arXiv
-
[71]
Abada, J
A. Abada, J. Kriewald and A.M. Teixeira, On the role of leptonic CPV phases in cLFV observables , Eur. Phys. J. C 81 (2021) 1016 [ 2107.06313]
2021 arXiv
-
[72]
Esteban, M.C
I. Esteban, M.C. Gonzalez-Garcia, M. Maltoni, I. Martinez-Soler, J.a.P. Pinheiro and T. Schwetz, NuFit-6.0: Updated global analysis of three-flavor neutrino oscillations , 2410.05380
-
[73]
Dev and A
P.S.B. Dev and A. Pilaftsis, Minimal Radiative Neutrino Mass Mechanism for Inverse Seesaw Models , Phys. Rev. D 86 (2012) 113001 [ 1209.4051]
2012 arXiv
-
[74]
’t Hooft, C
G. ’t Hooft, C. Itzykson, A. Jaffe, H. Lehmann, P.K. Mitter, I.M. Singer et al., Recent Developments in Gauge Theories. Proceedings, Nato Advanced Study Institute, Cargese, France, August 26 - September 8, 1979, vol. 59, pp. pp.1–438, 1980, DOI
1979
-
[75]
Hettmansperger, M
H. Hettmansperger, M. Lindner and W. Rodejohann, Phenomenological Consequences of sub-leading Terms in See-Saw Formulas , JHEP 04 (2011) 123 [ 1102.3432]. 29
2011 arXiv
-
[76]
Abada and M
A. Abada and M. Lucente, Looking for the minimal inverse seesaw realisation , Nucl. Phys. B 885 (2014) 651 [ 1401.1507]
2014 arXiv
-
[77]
Casas and A
J.A. Casas and A. Ibarra, Oscillating neutrinos and µ → e, γ, Nucl. Phys. B 618 (2001) 171 [hep-ph/0103065]
2001 arXiv
-
[78]
Urqu ´ ıa-Calder´ on, I
K.A. Urqu ´ ıa-Calder´ on, I. Timiryasov and O. Ruchayskiy,Bounds on heavy neutral leptons from tree level unitarity , 2409.13412
-
[79]
Chanowitz, M.A
M.S. Chanowitz, M.A. Furman and I. Hinchliffe, Weak Interactions of Ultraheavy Fermions. 2. , Nucl. Phys. B 153 (1979) 402
1979
-
[80]
Durand, J.M
L. Durand, J.M. Johnson and J.L. Lopez, Perturbative Unitarity Revisited: A New Upper Bound on the Higgs Boson Mass , Phys. Rev. Lett. 64 (1990) 1215
1990
-
[81]
Bernabeu, J.G
J. Bernabeu, J.G. Korner, A. Pilaftsis and K. Schilcher, Universality breaking effects in leptonic Z decays, Phys. Rev. Lett. 71 (1993) 2695 [ hep-ph/9307295]
1993 arXiv
-
[82]
Fajfer and A
S. Fajfer and A. Ilakovac, Lepton flavor violation in light hadron decays , Phys. Rev. D 57 (1998) 4219
1998
-
[83]
Ilakovac, Lepton flavor violation in the standard model extended by heavy singlet Dirac neutrinos , Phys
A. Ilakovac, Lepton flavor violation in the standard model extended by heavy singlet Dirac neutrinos , Phys. Rev. D 62 (2000) 036010 [ hep-ph/9910213]
2000 arXiv
-
[84]
Abada, J
A. Abada, J. Kriewald, E. Pinsard, S. Rosauro-Alcaraz and A.M. Teixeira, Heavy neutral lepton corrections to SM boson decays: lepton flavour universality violation in low-scale seesaw realisations , Eur. Phys. J. C 84 (2024) 149 [ 2307.02558]
2024 arXiv
-
[85]
Fernandez-Martinez, M.B
E. Fernandez-Martinez, M.B. Gavela, J. Lopez-Pavon and O. Yasuda, CP-violation from non-unitary leptonic mixing , Phys. Lett. B 649 (2007) 427 [ hep-ph/0703098]
2007 arXiv
-
[86]
Fernandez-Martinez, J
E. Fernandez-Martinez, J. Hernandez-Garcia, J. Lopez-Pavon and M. Lucente, Loop level constraints on Seesaw neutrino mixing , JHEP 10 (2015) 130 [ 1508.03051]
2015 arXiv
-
[87]
Fernandez-Martinez, J
E. Fernandez-Martinez, J. Hernandez-Garcia and J. Lopez-Pavon, Global constraints on heavy neutrino mixing, JHEP 08 (2016) 033 [ 1605.08774]
2016 arXiv
-
[88]
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]
2023 arXiv
-
[89]
Abada, J
A. Abada, J. Kriewald, E. Pinsard, S. Rosauro-Alcaraz and A.M. Teixeira, LFV Higgs and Z-boson decays: leptonic CPV phases and CP asymmetries , Eur. Phys. J. C 83 (2023) 494 [ 2207.10109]
2023 arXiv
-
[90]
MEG II collaboration, A search for µ+ → e+γ with the first dataset of the MEG II experiment , Eur. Phys. J. C 84 (2024) 216 [ 2310.12614]
2024 arXiv
-
[91]
MEG II collaboration, The design of the MEG II experiment , Eur. Phys. J. C 78 (2018) 380 [1801.04688]
2018 arXiv
-
[92]
BaBar collaboration, Searches for Lepton Flavor Violation in the Decays tau+- — > e+- gamma and tau+- — > mu+- gamma , Phys. Rev. Lett. 104 (2010) 021802 [ 0908.2381]
2010 arXiv
-
[93]
Belle-II collaboration, The Belle II Physics Book , PTEP 2019 (2019) 123C01 [ 1808.10567]
2019
-
[94]
Belle collaboration, Search for lepton-flavor-violating tau-lepton decays to ℓγ at Belle , JHEP 10 (2021) 19 [2103.12994]
2021 arXiv
-
[95]
SINDRUM collaboration, Search for the Decay µ+ → e+e+e−, Nucl. Phys. B 299 (1988) 1
1988
-
[96]
Blondel et al., Research Proposal for an Experiment to Search for the Decay µ → eee, 1301.6113
A. Blondel et al., Research Proposal for an Experiment to Search for the Decay µ → eee, 1301.6113
-
[97]
Hayasaka et al., Search for Lepton Flavor Violating Tau Decays into Three Leptons with 719 Million Produced Tau+Tau- Pairs, Phys
K. Hayasaka et al., Search for Lepton Flavor Violating Tau Decays into Three Leptons with 719 Million Produced Tau+Tau- Pairs, Phys. Lett. B 687 (2010) 139 [ 1001.3221]
2010 arXiv
-
[98]
Belle-II collaboration, Search for lepton-flavor-violating τ −→ µ−µ+µ− decays at Belle II , JHEP 09 (2024) 062 [ 2405.07386]
2024 arXiv
-
[99]
FCC collaboration, FCC Physics Opportunities: Future Circular Collider Conceptual Design Report Volume 1, Eur. Phys. J. C 79 (2019) 474
2019
-
[100]
SINDRUM IIcollaboration, A Search for muon to electron conversion in muonic gold , Eur. Phys. J. C 47 (2006) 337. 30
2006
-
[101]
DeeMe collaboration, Search for µ − e conversion with DeeMe experiment at J-PARC MLF , PoS FPCP2015 (2015) 060
2015
-
[102]
COMET collaboration, An Overview of the COMET Experiment and its Recent Progress , in 17th International Workshop on Neutrino Factories and Future Neutrino Facilities , 12, 2015 [ 1512.08564]
2015 arXiv
-
[103]
COMET collaboration, COMET Phase-I Technical Design Report , PTEP 2020 (2020) 033C01 [1812.09018]
2020 arXiv
-
[104]
COMET collaboration, Search for Muon-to-Electron Conversion with the COMET Experiment †, Universe 8 (2022) 196 [ 2203.06365]
2022 arXiv
-
[105]
Mu2e collaboration, Mu2e Technical Design Report, 1501.05241
-
[106]
Willmann et al., New bounds from searching for muonium to anti-muonium conversion , Phys
L. Willmann et al., New bounds from searching for muonium to anti-muonium conversion , Phys. Rev. Lett. 82 (1999) 49 [ hep-ex/9807011]
1999 arXiv
-
[107]
Bai et al., Conceptual Design of the Muonium-to-Antimuonium Conversion Experiment (MACE) , 2410.18817
A.-Y. Bai et al., Conceptual Design of the Muonium-to-Antimuonium Conversion Experiment (MACE) , 2410.18817
-
[108]
ATLAS collaboration, Search for the lepton flavor violating decay Z →eµ in pp collisions at √s TeV with the ATLAS detector , Phys. Rev. D 90 (2014) 072010 [ 1408.5774]
2014 arXiv
-
[109]
ATLAS collaboration, Search for lepton-flavor-violation in Z-boson decays with τ -leptons with the ATLAS detector, Phys. Rev. Lett. 127 (2022) 271801 [ 2105.12491]
2022 arXiv
-
[110]
Abada, A.M
A. Abada, A.M. Teixeira, A. Vicente and C. Weiland, Sterile neutrinos in leptonic and semileptonic decays, JHEP 02 (2014) 091 [ 1311.2830]
2014 arXiv
-
[111]
Abada, D
A. Abada, D. Das, A.M. Teixeira, A. Vicente and C. Weiland, Tree-level lepton universality violation in the presence of sterile neutrinos: impact for RK and Rπ, JHEP 02 (2013) 048 [ 1211.3052]
2013 arXiv
-
[112]
10.17181/CERN.FOZZ.ZP3Q
ATLAS collaboration, Technical Design Report for the ATLAS Inner Tracker Pixel Detector , 2017. 10.17181/CERN.FOZZ.ZP3Q
2017 doi
-
[113]
ATLAS collaboration, Search for high-mass resonances in final states with a τ -lepton and missing transverse momentum with the ATLAS detector , Phys. Rev. D 109 (2024) 112008 [ 2402.16576]
2024 arXiv
-
[114]
Patel, Package-X: A Mathematica package for the analytic calculation of one-loop integrals , Comput
H.H. Patel, Package-X: A Mathematica package for the analytic calculation of one-loop integrals , Comput. Phys. Commun. 197 (2015) 276 [ 1503.01469]
2015 arXiv
-
[115]
Shtabovenko, R
V. Shtabovenko, R. Mertig and F. Orellana, New Developments in FeynCalc 9.0 , Comput. Phys. Commun. 207 (2016) 432 [ 1601.01167]
2016 arXiv
-
[116]
Shtabovenko, R
V. Shtabovenko, R. Mertig and F. Orellana, FeynCalc 9.3: New features and improvements , Comput. Phys. Commun. 256 (2020) 107478 [ 2001.04407]
2020 arXiv
-
[117]
Shtabovenko, R
V. Shtabovenko, R. Mertig and F. Orellana, FeynCalc 10: Do multiloop integrals dream of computer codes?, Comput. Phys. Commun. 306 (2025) 109357 [ 2312.14089]
2025 arXiv
-
[118]
Santiago, D
J.L.G. Santiago, D. Portillo-S´ anchez, G. Hern´ andez-Tom´ e and J. Rend´ on,Authentic Majorana versus singlet Dirac neutrino contributions to µ+µ+→ℓ+ℓ+ ( ℓ=e,τ ) transitions, Phys. Rev. D 110 (2024) 053006 [2405.02819]
2024 arXiv
-
[119]
Sirlin, A Class of Useful Identities Involving Correlated Direct Products of γ Matrices, Nucl
A. Sirlin, A Class of Useful Identities Involving Correlated Direct Products of γ Matrices, Nucl. Phys. B 192 (1981) 93. 31
1981
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