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Searching for the lepton-flavor violating $γ γ e μ$ interaction at future $e^{-} e^{+}$ colliders

M. A. Arroyo-Ureña ^1,2,*, R. Gaitán^3,†, Marcela Marín ^3,4,‡, Humberto Salazar ^1,2,§, and M. G. Villanueva-Utrilla ^1,2,∥

¹Facultad de Ciencias Físico-Matemáticas, Benemérita Universidad Autónoma de Puebla, C.P. 72570, Puebla, México
²Centro Interdisciplinario de Investigación y Enseñanza de la Ciencia (CIIEC), Benemérita Universidad Autónoma de Puebla, C.P. 72570, Puebla, México
³Departamento de Física, FES-Cuautitlán, UNAM, C.P. 54770, Estado de México, México
⁴Instituto de Física, Universidad de Antioquia, Calle 70 # 52-21, Medellín, Colombia

^*Contact author: marco.arroyo@fcfm.buap.mx
^†Contact author: rgaitan@unam.mx
^‡Contact author: marcemarino8a@cuautitlan.unam.mx
^§Contact author: hsalazar@fcfm.buap.mx
^∥Contact author: maria.villanueva@alumno.buap.mx

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Phys. Rev. D 113, 035014 – Published 13 February, 2026

DOI: https://doi.org/10.1103/mvrj-qf6j

Abstract

We investigate the lepton flavor violating (LFV) process $e^{+} e^{-} \to e^{+} e^{-} e μ$ ( $e = e^{-}, e^{+}, μ = μ^{-}, μ^{+}$ ) at future circular colliders, probing the effective $γ γ e μ$ interaction through photon fusion. Within an effective field theory framework compatible with theoretical and experimental constraints, we identify regions in the parameter space of the effective couplings where the signal could be observed at the Circular Electron-Positron Collider at $\sqrt{s} = 240 GeV$ and the Future Circular Collider (FCC-ee) at $\sqrt{s} = 240$ and 350 GeV. Our analysis leverages distinctive kinematic distributions—particularly the transverse momentum of the scattered electron $p_{T}^{(e^{-} scattered)}$ and the central muon $p_{T}^{μ}$ —to achieve efficient signal-background separation. By employing a neural network classifier, we enhance the sensitivity beyond traditional cut-based methods, demonstrating the discovery potential of these facilities for LFV searches in the clean environment of $e^{+} e^{-}$ collisions.

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Phys. Rev. D 113, 035014– Published 13 February, 2026

Vol. 113, Iss. 3 — 1 February 2026

Received 8 September 2025
Accepted 15 January 2026

DOI: https://doi.org/10.1103/mvrj-qf6j

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Searching for the lepton-flavor violating $γ γ e μ$ interaction at future $e^{-} e^{+}$ colliders

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Searching for the lepton-flavor violating $γ γ e μ$ interaction at future $e^{-} e^{+}$ colliders