Right-handed electrons in radiative muon decay

Electrons emitted in the radiative decay μ^-→e^-ν¯_eν_μγ have a significant probability of being right-handed, even in the limit m_e→0. Such “wrong-helicity” electrons, arising from helicity-flip bremsstrahlung, contribute an amount {α}/{4π}Γ₀ to the muon decay width (Γ₀≡G_F²m_μ⁵/(192π³)). We use the helicity-flip splitting function D_hf(z) of Falk and Sehgal [Phys. Lett. B 325 (1994) 509] to obtain the spectrum of the right-handed electrons and the photons that accompany them. For a minimum photon energy E_γ=10 MeV (20 MeV), approximately 4% (7%) of electrons in radiative μ-decay are right-handed.