Probing Lepton Flavor Violation at FCC-ee

Abstract

We investigate the prospects for probing Lepton Flavor Violation (LFV) at FCC-ee within the Standard Model Effective Field Theory (SMEFT) framework. The approximately 2 × 10¹¹ τ-lepton pairs expected at the Z-pole run of FCC-ee could improve current limits on the branching fractions of τ→3ℓ and τ→ℓγ (ℓ=e,μ) by factors ranging from 30 to 800, depending on the specific channel. We compare the resulting new-physics reach with that obtained from searches for Z → τℓ and h → τℓ, which have so far received greater attention in studies of LFV at future e⁺e^- colliders. We find that τ decays can surpass both the current and the projected sensitivity of Z→τℓ searches to the same LFV interactions, while probing a broader range of SMEFT operators. We further show that, for LFV Yukawa-like interactions, direct searches for h→τℓ provide the strongest sensitivity. By contrast, for semileptonic operators that radiatively induce LFV Higgs decays, this hierarchy can be reversed, with τ decays providing the leading probe.

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BibTeX RIS

BibTeX

@misc{allwicher2026probing,
  title = {{Probing Lepton Flavor Violation at FCC-ee}},
  author = {L. Allwicher and R. Bartocci and M. Cepeda and C. Cornella and L. P. S. Leal and A. Lusiani and C. Martin Perez and P. Paradisi and E. Scantamburlo and O. Sumensari},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.27057},
  eprint = {2610.27057},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.27057},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Probing Lepton Flavor Violation at FCC-ee
AU  - L. Allwicher
AU  - R. Bartocci
AU  - M. Cepeda
AU  - C. Cornella
AU  - L. P. S. Leal
AU  - A. Lusiani
AU  - C. Martin Perez
AU  - P. Paradisi
AU  - E. Scantamburlo
AU  - O. Sumensari
PY  - 2026
DA  - 2026/10/19
PB  - arXiv
DO  - 10.48550/arxiv.2610.27057
UR  - https://arxiv.org/abs/2610.27057
AB  - We investigate the prospects for probing Lepton Flavor Violation (LFV) at FCC-ee within the Standard Model Effective Field Theory (SMEFT) framework. The approximately 2 × 10^11 τ-lepton pairs expected at the Z-pole run of FCC-ee could improve current limits on the branching fractions of τ→3ℓ and τ→ℓγ (ℓ=e,μ) by factors ranging from 30 to 800, depending on the specific channel. We compare the resulting new-physics reach with that obtained from searches for Z → τℓ and h → τℓ, which have so far received greater attention in studies of LFV at future e^+e^- colliders. We find that τ decays can surpass both the current and the projected sensitivity of Z→τℓ searches to the same LFV interactions, while probing a broader range of SMEFT operators. We further show that, for LFV Yukawa-like interactions, direct searches for h→τℓ provide the strongest sensitivity. By contrast, for semileptonic operators that radiatively induce LFV Higgs decays, this hierarchy can be reversed, with τ decays providing the leading probe.
ER  -

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