Abstract
Lepton Flavour Violation (LFV) is New Physics that must occur, but is stringently constrained by experiments searching for μ ↔ e flavour change, such as μ → eγ, μ → \( e\overline{e}e \) or μ → e conversion. However, in an Effective Field Theory(EFT) parametrisation, there are many more μ ↔ e operators than restrictive constraints, so determining operator coefficients from data is a remote dream. It is nonetheless interesting to learn about New Physics from data, so this manuscript introduces “observable-vectors” in the space of operator coefficients, which identify at any scale the combination of coefficients probed by the observable. These vectors have an overlap ≳ 10−3 with most of the coefficients, and are used to study whether μ → eγ, μ → \( e\overline{e}e \) and μ → e conversion give complementary information about New Physics. The appendix gives updated sensitivities of these processes, (and a subset of τ → ℓ decays), to operator coefficients at the weak scale in the SMEFT and in the EFT below mW.
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Davidson, S. Completeness and complementarity for μ → eγ, μ → \( e\overline{e}e \) and μA → eA. J. High Energ. Phys. 2021, 172 (2021). https://doi.org/10.1007/JHEP02(2021)172
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DOI: https://doi.org/10.1007/JHEP02(2021)172