  Electrons emitted in the radiative decay mu^- -> e^- anti-nu_e nu_mu gamma
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 alpha/(4 pi) Gamma_0 to the muon decay
width (Gamma_0 = G_F^2 m^5_mu/ (192 pi^3)). We use the helicity-flip splitting
function D_hf (z) of Falk and Sehgal (Phys. Lett. B 325, 509 (1994)) to obtain
the spectrum of the right-handed electrons and the photons that accompany them.
For a minimum photon energy E_gamma = 10 MeV (20 MeV), approximately 4% (7%) of
electrons in radiative mu-decay are right-handed.

High Energy Physics - Phenomenology