我們研究在Belle II的B工廠實驗中與親輕子類軸子(X)有關的帶電味破 壞。我們聚焦在類軸子透過濤子衰變生成τ → Xl(l = e, μ)，以及其自身衰 變X → l−l+。類軸子能夠立即衰變或是長壽的。我們進行蒙地卡羅模擬，重 建Belle有關濤子味破壞的立即性衰變，並提出位移頂點的搜索。對於兩種型態 的搜索，我們以類軸子的質量與壽命為函數，在產物的分之係數和類軸子的耦 合常數中，導源出Belle II的靈敏度。結果顯示位移節點的搜索在長衰變距離的 範圍，能以約40倍的相對分支係數超越立即衰變搜索的靈敏度。

We study charged lepton flavor violation associated with a light leptophillic axion-like particle (ALP), X, at the B-factory experiment, Belle II. We focus on production of the ALP in tau decays τ → Xl with l = e,μ, followed by its decay via X → l−l+. The ALP can either promptly decaying or long-lived. We perform Monte-Carlo simulations, recasting a prompt search at Belle for lepton- flavor-violating τ decays, and propose a displaced-vertex (DV) search. For both types of searches, we derive the Belle II sensitivity reaches in both the product of branching fractions and the ALP coupling constants, as functions of the ALP mass and lifetime. The results show that the DV search exceeds the sensitivity reach of the prompt search to the relevant branching fractions by up to about a factor of 40 in the long decay length regime.

Contents ii
List of Tables iii
List of Figures v
1 Introduction … 1
2 Model 5
2.1 Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Benchmark Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Constraints 10
3.1 LEP...................................... 10
3.2 Supernova................................... 11
3.3 τ→3l..................................... 12
3.4 Leptonuniversalityτ→lνν ̄......................... 13
3.5 τ→lγ..................................... 14
3.6 Leptonicdecaysofthemuons........................ 15
3.7 Leptonicg−2anomalies........................... 16
3.8 Beam-dumpanddark-photonsearches ................... 17
3.9 Muonium-antimuonium oscillations and μ− → e− conversion . . . . . . . 18
4 Simulation 19
4.1 Experiment,EventSelections,andSimulation . . . . . . . . . . . . . . . 19
4.1.1 Recastofthepromptsearch..................... 20
4.1.2 Proposalofadisplaced-vertexsearch. . . . . . . . . . . . . . . . 21
4.1.3 ComputationandSimulation .................... 21

5 Results 23
5.1 NumericalResults .............................. 23
5.1.1 Scenario1:gτeandgee........................ 23
5.1.2 Scenario2:gτμandgμμ ....................... 27
5.1.3 OtherScenarios............................ 29
6 Conclusions 31

[1] C. Abel et al. “Measurement of the permanent electric dipole moment of the neutron”. In: Phys. Rev. Lett. 124.8 (2020), p. 081803. doi: 10.1103/ PhysRevLett.124.081803. arXiv: 2001.11966 [hep-ex].
[2] Jack Dragos et al. “Confirming the Existence of the strong CP Problem in Lattice QCD with the Gradient Flow”. In: Phys. Rev. C 103.1 (2021), p. 015202. doi:10.1103/PhysRevC.103.015202. arXiv: 1902.03254 [hep-lat].
[3] R. D. Peccei and Helen R. Quinn. “Constraints Imposed by CP Conserva- tion in the Presence of Instantons”. In: Phys. Rev. D 16 (1977), pp. 1791– 1797. doi:10.1103/PhysRevD.16.1791.
[4] R. D. Peccei. “The Strong CP problem and axions”. In: Lect. Notes Phys. 741 (2008). Ed. by Markus Kuster, Georg Raffelt, and Berta Beltran, pp. 3– 17. doi: 10.1007/978-3-540-73518-2_1. arXiv: hep-ph/0607268.
[5] P. A. Zyla et al. “Review of Particle Physics”. In: PTEP 2020.8 (2020), p. 083C01. doi: 10.1093/ptep/ptaa104.
[6] Jonathan L. Feng et al. “Third generation familons, b factories, and neu- trino cosmology”. In: Phys. Rev. D 57 (1998), pp. 5875–5892. doi: 10. 1103/PhysRevD.57.5875. arXiv: hep-ph/9709411.
[7] Michael Dine and Willy Fischler. “The Not So Harmless Axion”. In: Phys. Lett. B 120 (1983). Ed. by M. A. Srednicki, pp. 137–141. doi: 10.1016/ 0370-2693(83)90639-1.
[8] L. F. Abbott and P. Sikivie. “A Cosmological Bound on the Invisible Ax- ion”. In: Phys. Lett. B 120 (1983). Ed. by M. A. Srednicki, pp. 133–136. doi: 10.1016/0370-2693(83)90638-X.

[9] John Preskill, Mark B. Wise, and Frank Wilczek. “Cosmology of the Invis- ible Axion”. In: Phys. Lett. B 120 (1983). Ed. by M. A. Srednicki, pp. 127– 132. doi: 10.1016/0370-2693(83)90637-8.
[10] David J. E. Marsh. “Axion Cosmology”. In: Phys. Rept. 643 (2016), pp. 1–
79. doi: 10.1016/j.physrep.2016.06.005. arXiv: 1510.07633 [astro-ph.CO].
[11] Gaetano Lambiase and Subhendra Mohanty. “Hydrogen spin oscillations in a background of axions and the 21-cm brightness temperature”. In: Mon. Not. Roy. Astron. Soc. 494.4 (2020), pp. 5961–5966. doi: 10.1093/mnras/ staa1070. arXiv: 1804.05318 [hep-ph].
[12] Adrien Auriol, Sacha Davidson, and Georg Raffelt. “Axion absorption and the spin temperature of primordial hydrogen”. In: Phys. Rev. D 99.2 (2019), p. 023013. doi: 10.1103/PhysRevD.99.023013. arXiv: 1808.09456 [hep-ph].
[13] Nick Houston et al. “Natural Explanation for 21 cm Absorption Signals via Axion-Induced Cooling”. In: Phys. Rev. Lett. 121.11 (2018), p. 111301. doi:10.1103/PhysRevLett.121.111301. arXiv: 1805.04426 [hep-ph].
[14] Jihn E. Kim and David J. E. Marsh. “An ultralight pseudoscalar boson”. In: Phys. Rev. D 93.2 (2016), p. 025027. doi: 10.1103/PhysRevD.93.025027. arXiv: 1510.01701 [hep-ph].
[15] Ivan De Martino et al. “Recognizing Axionic Dark Matter by Compton and de Broglie Scale Modulation of Pulsar Timing”. In: Phys. Rev. Lett. 119.22 (2017), p. 221103. doi: 10.1103/PhysRevLett.119.221103. arXiv: 1705.04367 [astro-ph.CO].
[16] V. A. Rubakov. “Grand unification and heavy axion”. In: JETP Lett. 65 (1997), pp. 621–624. doi: 10.1134/1.567390. arXiv: hep-ph/9703409.
[17] Joerg Jaeckel and Michael Spannowsky. “Probing MeV to 90 GeV axion-like particles with LEP and LHC”. In: Phys. Lett. B 753 (2016), pp. 482–487. doi: 10.1016/j.physletb.2015.12.037. arXiv: 1509.00476 [hep-ph].
[18] I. Brivio et al. “ALPs Effective Field Theory and Collider Signatures”. In: Eur. Phys. J. C 77.8 (2017), p. 572. doi: 10.1140/epjc/s10052-017- 5111-3. arXiv: 1701.05379 [hep-ph].

[19] Matthew J. Dolan et al. “Revised constraints and Belle II sensitivity for visible and invisible axion-like particles”. In: JHEP 12 (2017). [Erratum: JHEP 03, 190 (2021)], p. 094. doi: 10.1007/JHEP12(2017)094. arXiv: 1709.00009 [hep-ph].
[20] Brando Bellazzini et al. “R-axion at colliders”. In: Phys. Rev. Lett. 119.14 (2017), p. 141804. doi: 10.1103/PhysRevLett.119.141804. arXiv: 1702. 02152 [hep-ph].
[21] Martin Bauer, Matthias Neubert, and Andrea Thamm. “Collider Probes of Axion-Like Particles”. In: JHEP 12 (2017), p. 044. doi: 10.1007/ JHEP12(2017)044. arXiv: 1708.00443 [hep-ph].
[22] Simon Knapen et al. “LHC limits on axion-like particles from heavy-ion collisions”. In: CERN Proc. 1 (2018). Ed. by David d’Enterria, Albert de Roeck, and Michelangelo Mangano, p. 65. doi: 10.23727/CERN-Proceedings- 2018-001.65. arXiv: 1709.07110 [hep-ph].
[23] Martin Bauer et al. “Axion-Like Particles at Future Colliders”. In: Eur. Phys. J. C 79.1 (2019), p. 74. doi: 10.1140/epjc/s10052-019-6587-9. arXiv: 1808.10323 [hep-ph].
[24] Daniel Aloni, Yotam Soreq, and Mike Williams. “Coupling QCD-Scale Ax- ionlike Particles to Gluons”. In: Phys. Rev. Lett. 123.3 (2019), p. 031803. doi:10.1103/PhysRevLett.123.031803. arXiv: 1811.03474 [hep-ph].
[25] Adrian Carmona, Christiane Scherb, and Pedro Schwaller. “Charming ALPs”. In: (Jan. 2021). arXiv: 2101.07803 [hep-ph].
[26] F. Abudin ́en et al. “Search for Axion-Like Particles produced in e+e− col- lisions at Belle II”. In: Phys. Rev. Lett. 125.16 (2020), p. 161806. doi: 10.1103/PhysRevLett.125.161806. arXiv: 2007.13071 [hep-ex].
[27] Julian Heeck. “Interpretation of Lepton Flavor Violation”. In: Phys. Rev. D 95.1 (2017), p. 015022. doi: 10.1103/PhysRevD.95.015022. arXiv: 1610.07623 [hep-ph].

[28] S. T. Petcov. “The Processes μ → e+γ,μ → e+e,ν′ → ν +γ in the Weinberg-Salam Model with Neutrino Mixing”. In: Sov. J. Nucl. Phys. 25 (1977). [Erratum: Sov.J.Nucl.Phys. 25, 698 (1977), Erratum: Yad.Fiz. 25, 1336 (1977)], p. 340.
[29] G. Herna ́ndez-Tom ́e, G. L ́opez Castro, and P. Roig. “Flavor violating lep- tonic decays of τ and μ leptons in the Standard Model with massive neu- trinos”. In: Eur. Phys. J. C 79.1 (2019). [Erratum: Eur.Phys.J.C 80, 438 (2020)], p. 84. doi:10.1140/epjc/s10052-019-6563-4. arXiv: 1807. 06050 [hep-ph].
[30] A. M. Baldini et al. “Search for the lepton flavour violating decay μ+ → e+γ with the full dataset of the MEG experiment”. In: Eur. Phys. J. C 76.8 (2016), p. 434. doi: 10.1140/epjc/s10052-016-4271-x. arXiv: 1605. 05081 [hep-ex].
[31] U. Bellgardt et al. “Search for the Decay mu+ —> e+ e+ e-”. In: Nucl. Phys. B 299 (1988), pp. 1–6. doi: 10.1016/0550-3213(88)90462-2.
[32] A. Blondel et al. “Research Proposal for an Experiment to Search for the Decay μ → eee”. In: (Jan. 2013). arXiv: 1301.6113 [physics.ins-det].
[33] A. M. Baldini et al. “MEG Upgrade Proposal”. In: (Jan. 2013). arXiv: 1301.7225 [physics.ins-det].
[34] Adriana Cordero-Cid, G. Tavares-Velasco, and J. J. Toscano. “Implications of a very light pseudoscalar boson on lepton flavor violation”. In: Phys. Rev. D 72 (2005), p. 117701. doi: 10.1103/PhysRevD.72.117701. arXiv: hep-ph/0511331.
[35] P. S. Bhupal Dev, Rabindra N. Mohapatra, and Yongchao Zhang. “Lepton Flavor Violation Induced by a Neutral Scalar at Future Lepton Colliders”. In: Phys. Rev. Lett. 120.22 (2018), p. 221804. doi: 10.1103/PhysRevLett. 120.221804. arXiv: 1711.08430 [hep-ph].
[36] Martin Bauer et al. “Axionlike Particles, Lepton-Flavor Violation, and a New Explanation of aμ and ae”. In: Phys. Rev. Lett. 124.21 (2020), p. 211803. doi: 10.1103/PhysRevLett.124.211803. arXiv: 1908.00008 [hep-ph].

[37] Claudia Cornella, Paride Paradisi, and Olcyr Sumensari. “Hunting for ALPs with Lepton Flavor Violation”. In: JHEP 01 (2020), p. 158. doi: 10.1007/ JHEP01(2020)158. arXiv: 1911.06279 [hep-ph].
[38] Lorenzo Calibbi et al. “Looking forward to Lepton-flavor-violating ALPs”. In: (June 2020). arXiv: 2006.04795 [hep-ph].
[39] Motoi Endo, Syuhei Iguro, and Teppei Kitahara. “Probing eμ flavor-violating ALP at Belle II”. In: JHEP 06 (2020), p. 040. doi: 10.1007/JHEP06(2020) 040. arXiv:2002.05948 [hep-ph].
[40] Brian Batell, Maxim Pospelov, and Adam Ritz. “Multi-lepton Signatures of a Hidden Sector in Rare B Decays”. In: Phys. Rev. D 83 (2011), p. 054005. doi: 10.1103/PhysRevD.83.054005. arXiv: 0911.4938 [hep-ph].
[41] Jernej F. Kamenik and Christopher Smith. “FCNC portals to the dark sector”. In: JHEP 03 (2012), p. 090. doi: 10.1007/JHEP03(2012)090. arXiv: 1111.6402 [hep-ph].
[42] M. B. Gavela et al. “Flavor constraints on electroweak ALP couplings”. In: Eur. Phys. J. C 79.5 (2019), p. 369. doi: 10.1140/epjc/s10052-019- 6889-y. arXiv:1901.02031 [hep-ph].
[43] T. Abe et al. “Belle II Technical Design Report”. In: (Nov. 2010). arXiv: 1011.0352 [physics.ins-det].
[44] W. Altmannshofer et al. “The Belle II Physics Book”. In: PTEP 2019.12 (2019). Ed. by E. Kou and P. Urquijo. [Erratum: PTEP 2020, 029201 (2020)], p. 123C01. doi: 10.1093/ptep/ptz106. arXiv: 1808.10567 [hep-ex].
[45] Michel Hern ́andez Villanueva. “Prospects for τ lepton physics at Belle II”. In: SciPost Phys. Proc. 1 (2019), p. 003. doi: 10.21468/SciPostPhysProc. 1.003. arXiv:1812.04225 [hep-ex].
[46] Francesco Tenchini et al. “First results and prospects for tau LFV decay τ → e + α(invisible) at Belle II”. In: PoS ICHEP2020 (2021), p. 288. doi: 10.22323/1.390.0288.

[47] Rouven Essig et al. “Discovering New Light States at Neutrino Experi- ments”. In: Phys. Rev. D 82 (2010), p. 113008. doi: 10.1103/PhysRevD. 82.113008. arXiv:1008.0636 [hep-ph].
[48] Sarah Andreas et al. “Constraints on a very light CP-odd Higgs of the NMSSM and other axion-like particles”. In: JHEP 08 (2010), p. 003. doi: 10.1007/JHEP08(2010)003. arXiv: 1005.3978 [hep-ph].
[49] J. P. Lees et al. “Search for a muonic dark force at BABAR”. In: Phys. Rev. D 94.1 (2016), p. 011102. doi: 10.1103/PhysRevD.94.011102. arXiv: 1606.03501 [hep-ex].
[50] Syuhei Iguro, Yuji Omura, and Michihisa Takeuchi. “Probing μτ flavor- violating solutions for the muon g − 2 anomaly at Belle II”. In: JHEP 09 (2020), p. 144. doi:10.1007/JHEP09(2020)144. arXiv: 2002.12728 [hep-ph].
[51] A. Abashian et al. “The Belle Detector”. In: Nucl. Instrum. Meth. A 479 (2002), pp. 117–232. doi: 10.1016/S0168-9002(01)02013-7.
[52] K. Hayasaka et al. “Search for Lepton Flavor Violating Tau Decays into Three Leptons with 719 Million Produced Tau+Tau- Pairs”. In: Phys. Lett. B 687 (2010), pp. 139–143. doi: 10.1016/j.physletb.2010.03.037. arXiv: 1001.3221 [hep-ex].
[53] J. P. Lees et al. “Limits on tau Lepton-Flavor Violating Decays in three charged leptons”. In: Phys. Rev. D 81 (2010), p. 111101. doi: 10.1103/ PhysRevD.81.111101. arXiv: 1002.4550 [hep-ex].
[54] David Curtin et al. “Long-Lived Particles at the Energy Frontier: The MATHUSLA Physics Case”. In: Rept. Prog. Phys. 82.11 (2019), p. 116201. doi: 10.1088/1361-6633/ab28d6. arXiv: 1806.07396 [hep-ph].
[55] Lawrence Lee et al. “Collider Searches for Long-Lived Particles Beyond the Standard Model”. In: Prog. Part. Nucl. Phys. 106 (2019), pp. 210–255. doi: 10.1016/j.ppnp.2019.02.006. arXiv: 1810.12602 [hep-ph].
[56] Juliette Alimena et al. “Searching for long-lived particles beyond the Stan- dard Model at the Large Hadron Collider”. In: J. Phys. G 47.9 (2020), p. 090501. doi: 10.1088/1361-6471/ab4574. arXiv: 1903.04497 [hep-ex].

[57] C. O. Dib et al. “Searching for a sterile neutrino that mixes predominantly with ντ at B factories”. In: Phys. Rev. D 101.9 (2020), p. 093003. doi: 10.1103/PhysRevD.101.093003. arXiv: 1908.09719 [hep-ph].
[58] C. S. Kim et al. “Probing sterile neutrinos in B(D) meson decays at Belle II (BESIII)”. In: Eur. Phys. J. C 80.8 (2020), p. 730. doi: 10.1140/epjc/ s10052-020-8310-2. arXiv:1908.00376 [hep-ph].
[59] Dong Woo Kang, P. Ko, and Chih-Ting Lu. “Exploring properties of long- lived particles in inelastic dark matter models at Belle II”. In: JHEP 04 (2021), p. 269. doi: 10.1007/JHEP04(2021)269. arXiv: 2101.02503 [hep-ph].
[60] Mason Acevedo et al. “Multi-track Displaced Vertices at B-Factories”. In: (May 2021). arXiv: 2105.12744 [hep-ph].
[61] Sascha Dreyer et al. “Physics reach of a long-lived particle detector at Belle II”. In: (May 2021). arXiv: 2105.12962 [hep-ph].
[62] Michael Duerr et al. “Invisible and displaced dark matter signatures at Belle II”. In: JHEP 02 (2020), p. 039. doi: 10.1007/JHEP02(2020)039. arXiv: 1911.03176 [hep-ph].
[63] Michael Duerr et al. “Long-lived Dark Higgs and Inelastic Dark Matter at Belle II”. In: JHEP 04 (2021), p. 146. doi: 10.1007/JHEP04(2021)146. arXiv: 2012.08595 [hep-ph].
[64] Anastasiia Filimonova, Ruth Scha ̈fer, and Susanne Westhoff. “Probing dark sectors with long-lived particles at BELLE II”. In: Phys. Rev. D 101.9 (2020), p. 095006. doi:10.1103/PhysRevD.101.095006. arXiv: 1911. 03490 [hep-ph].
[65] Xin Chen et al. “Search for dark photon and dark matter signatures around electron-positron colliders”. In: Phys. Lett. B 814 (2021), p. 136076. doi:10.1016/j.physletb.2021.136076. arXiv: 2001.04382 [hep-ph].
[66] Sourav Dey et al. “Long-lived light neutralinos at Belle II”. In: JHEP 02 (2021), p. 211. doi: 10.1007/JHEP02(2021)211. arXiv: 2012.00438 [hep-ph].

[67] Julian Heeck and Werner Rodejohann. “Lepton flavor violation with dis- placed vertices”. In: Phys. Lett. B 776 (2018), pp. 385–390. doi: 10.1016/ j.physletb.2017.11.067. arXiv: 1710.02062 [hep-ph].
[68] H. Albrecht et al. “A Search for lepton flavor violating decays tau —-> e alpha, tau —> mu alpha”. In: Z. Phys. C 68 (1995), pp. 25–28. doi: 10.1007/BF01579801.
[69] T. Yoshinobu and K. Hayasaka. “MC study for the lepton flavor violating tau decay into a lepton and an undetectable particle”. In: Nucl. Part. Phys. Proc. 287-288 (2017). Ed. by Changzheng Yuan, Xiaohu Mo, and Liangliang Wang, pp. 218–220. doi:10.1016/j.nuclphysbps.2017.03.081.
[70] Diego Guadagnoli, Chan Beom Park, and Francesco Tenchini. “τ → l+ invisible through invisible-savvy collider variables”. In: (June 2021). arXiv: 2106.16236 [hep-ph].
[71] E. De La Cruz-Burelo, M. Hernandez-Villanueva, and A. De Yta-Hernandez. “New method for beyond the Standard Model invisible particle searches in tau lepton decays”. In: Phys. Rev. D 102.11 (2020), p. 115001. doi: 10.1103/PhysRevD.102.115001. arXiv:2007.08239 [hep-ph].
[72] Kai Ma. “Polarization Effects in Lepton Flavor Violated Decays Induced by Axion-Like Particles”. In: (Apr. 2021). arXiv: 2104.11162 [hep-ph].
[73] S. Schael et al. “Fermion pair production in e+e− collisions at 189-209-GeV and constraints on physics beyond the standard model”. In: Eur. Phys. J. C 49 (2007), pp. 411–437. doi: 10.1140/epjc/s10052-006-0156-8. arXiv: hep-ex/0609051.
[74] Neil D. Christensen and Claude Duhr. “FeynRules - Feynman rules made easy”. In: Comput. Phys. Commun. 180 (2009), pp. 1614–1641. doi: 10. 1016/j.cpc.2009.02.018. arXiv: 0806.4194 [hep-ph].
[75] Adam Alloul et al. “FeynRules 2.0 - A complete toolbox for tree-level phe- nomenology”. In: Comput. Phys. Commun. 185 (2014), pp. 2250–2300. doi: 10.1016/j.cpc.2014.04.012. arXiv: 1310.1921 [hep-ph].

[76] Celine Degrande et al. “UFO - The Universal FeynRules Output”. In: Com- put. Phys. Commun. 183 (2012), pp. 1201–1214. doi: 10.1016/j.cpc. 2012.01.022. arXiv: 1108.2040 [hep-ph].
[77] J. Alwall et al. “The automated computation of tree-level and next-to- leading order differential cross sections, and their matching to parton shower simulations”. In: JHEP 07 (2014), p. 079. doi: 10.1007/JHEP07(2014)079. arXiv: 1405.0301 [hep-ph].
[78] P. L. Anthony et al. “Precision measurement of the weak mixing angle in Moller scattering”. In: Phys. Rev. Lett. 95 (2005), p. 081601. doi: 10.1103/ PhysRevLett.95.081601. arXiv: hep-ex/0504049.
[79] A. L. Hallin et al. “Sensitive search for resonances in low-energy e+ e- scattering”. In: Phys. Rev. D 45 (1992), pp. 3955–3960. doi: 10.1103/ PhysRevD.45.3955.
[80] Gholamhossein Haghighat and Mojtaba Mohammadi Najafabadi. “Search for lepton-flavor-violating ALPs at a future muon collider and utilization of polarization-induced effects”. In: (June 2021). arXiv: 2106.00505 [hep-ph].
[81] Jean Pierre Delahaye et al. “Muon Colliders”. In: (Jan. 2019). arXiv: 1901. 06150 [physics.acc-ph].
[82] Manuela Boscolo, Jean-Pierre Delahaye, and Mark Palmer. “The future prospects of muon colliders and neutrino factories”. In: Rev. Accel. Sci. Tech. 10.01 (2019), pp. 189–214. doi: 10.1142/9789811209604_0010. arXiv: 1808.01858 [physics.acc-ph].
[83] Hind Al Ali et al. “The Muon Smasher’s Guide”. In: (Mar. 2021). arXiv: 2103.14043 [hep-ph].
[84] Robert Bollig et al. “Muons in Supernovae: Implications for the Axion- Muon Coupling”. In: Phys. Rev. Lett. 125.5 (2020). [Erratum: Phys.Rev.Lett. 126, 189901 (2021)], p. 051104. doi: 10.1103/PhysRevLett.125.051104. arXiv: 2005.07141 [hep-ph].
[85] Giuseppe Lucente and Pierluca Carenza. “Supernova bound on Axion- Like Particles coupled with electrons”. In: (July 2021). arXiv: 2107.12393 [hep-ph].

[86] Patrick Foldenauer and Joerg Jaeckel. “Purely flavor-changing Z’ bosons and where they might hide”. In: JHEP 05 (2017), p. 010. doi: 10.1007/ JHEP05(2017)010. arXiv: 1612.07789 [hep-ph].
[87] Wolfgang Altmannshofer et al. “Lepton flavor violating Z’ explanation of the muon anomalous magnetic moment”. In: Phys. Lett. B 762 (2016), pp. 389–398. doi: 10.1016/j.physletb.2016.09.046. arXiv: 1607.06832 [hep-ph].
[88] Antonio Pich. “Precision Tau Physics”. In: Prog. Part. Nucl. Phys. 75 (2014), pp. 41–85. doi: 10.1016/j.ppnp.2013.11.002. arXiv: 1310.7922 [hep-ph].
[89] Bernard Aubert et al. “Measurements of Charged Current Lepton Uni- versality and |Vus| using Tau Lepton Decays to e−ν ̄eντ, μ−ν ̄μντ, π−ντ, and K−ντ”. In: Phys. Rev. Lett. 105 (2010), p. 051602. doi: 10.1103/ PhysRevLett.105.051602. arXiv: 0912.0242 [hep-ex].
[90] Bernard Aubert et al. “Searches for Lepton Flavor Violation in the Decays tau+- —> e+- gamma and tau+- —> mu+- gamma”. In: Phys. Rev. Lett. 104 (2010), p. 021802. doi: 10.1103/PhysRevLett.104.021802. arXiv: 0908.2381 [hep-ex].
[91] L ́eoMoreletal.“Determinationofthefine-structureconstantwithan accuracy of 81 parts per trillion”. In: Nature 588.7836 (2020), pp. 61–65. doi: 10.1038/s41586-020-2964-7.
[92] B. Abi et al. “Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm”. In: Phys. Rev. Lett. 126.14 (2021), p. 141801. doi:10.1103/PhysRevLett.126.141801. arXiv: 2104.03281 [hep-ex].
[93] G. W. Bennett et al. “Final Report of the Muon E821 Anomalous Magnetic Moment Measurement at BNL”. In: Phys. Rev. D 73 (2006), p. 072003. doi: 10.1103/PhysRevD.73.072003. arXiv: hep-ex/0602035.
[94] T. Aoyama et al. “The anomalous magnetic moment of the muon in the Standard Model”. In: Phys. Rept. 887 (2020), pp. 1–166. doi: 10.1016/j. physrep.2020.07.006. arXiv: 2006.04822 [hep-ph].

[95] Manuel A. Buen-Abad et al. “Challenges for an axion explanation of the muon g − 2 measurement”. In: (Apr. 2021). arXiv: 2104.03267 [hep-ph].
[96] Wai-Yee Keung, Danny Marfatia, and Po-Yan Tseng. “Axion-like particles, two-Higgs-doublet models, leptoquarks, and the electron and muon g-2”. In: LHEP 2021 (2021), p. 209. arXiv: 2104.03341 [hep-ph].
[97] Sz. Borsanyi et al. “Leading hadronic contribution to the muon magnetic moment from lattice QCD”. In: Nature 593.7857 (2021), pp. 51–55. doi: 10.1038/s41586-021-03418-1. arXiv: 2002.12347 [hep-lat].
[98] L. Willmann et al. “New bounds from searching for muonium to anti- muonium conversion”. In: Phys. Rev. Lett. 82 (1999), pp. 49–52. doi: 10. 1103/PhysRevLett.82.49. arXiv: hep-ex/9807011.
[99] Lorenzo Calibbi and Giovanni Signorelli. “Charged Lepton Flavour Vio- lation: An Experimental and Theoretical Introduction”. In: Riv. Nuovo Cim. 41.2 (2018), pp. 71–174. doi: 10.1393/ncr/i2018-10144-0. arXiv: 1709.00294 [hep-ph].
[100] Wilhelm H. Bertl et al. “A Search for muon to electron conversion in muonic gold”. In: Eur. Phys. J. C 47 (2006), pp. 337–346. doi: 10.1140/epjc/ s2006-02582-x.
[101] L. Bartoszek et al. “Mu2e Technical Design Report”. In: (Oct. 2014). doi:10.2172/1172555. arXiv: 1501.05241 [physics.ins-det].
[102] R. Abramishvili et al. “COMET Phase-I Technical Design Report”. In: PTEP 2020.3 (2020), p. 033C01. doi: 10.1093/ptep/ptz125. arXiv: 1812. 09018 [physics.ins-det].
[103] Julian Heeck. “Lepton flavor violation with light vector bosons”. In: Phys. Lett. B 758 (2016), pp. 101–105. doi: 10.1016/j.physletb.2016.05.007. arXiv: 1602.03810 [hep-ph].
[104] Chuan-Hung Chen and Takaaki Nomura. “Lμ −Lτ gauge-boson production from lepton flavor violating τ decays at Belle II”. In: Phys. Rev. D 96.9 (2017), p. 095023. doi: 10.1103/PhysRevD.96.095023. arXiv: 1704.04407 [hep-ph].

[105] Thomas Flacke et al. “Phenomenology of relaxion-Higgs mixing”. In: JHEP 06 (2017), p. 050. doi: 10.1007/JHEP06(2017)050. arXiv: 1610.02025 [hep-ph].
[106] P. S. Bhupal Dev, Rabindra N. Mohapatra, and Yongchao Zhang. “Dis- placed photon signal from a possible light scalar in minimal left-right see- saw model”. In: Phys. Rev. D 95.11 (2017), p. 115001. doi: 10.1103/ PhysRevD.95.115001. arXiv: 1612.09587 [hep-ph].
[107] P. S. Bhupal Dev, Rabindra N. Mohapatra, and Yongchao Zhang. “Long Lived Light Scalars as Probe of Low Scale Seesaw Models”. In: Nucl. Phys. B 923 (2017), pp. 179–221. doi: 10.1016/j.nuclphysb.2017.07.021. arXiv: 1703.02471 [hep-ph].