Lepton universality in anomalous l+l-γ events

Adopting five representative models so far proposed to explain the anomalous l+l-γ events i.e. I) Z0 → S or P + γ →l+l-γ, II) Z0 → Zsub(virt)sup(0) + γ → l+l-γ (anomalous magnetic-moment interaction), III) Z0 → l-barlsup(*) + ll-bar sup(*) → l+l-γ (excited lepton), IV) S or P →Zsub(virt)sup(0) + γ → l+l-γ and V) standard bremsstrahlung, it is studied to what extent the lepton universality in these anomalous events is affected by finite leptons mass effects. It is shown that the lepton universality is very well satisfied in models I, II and IV, while very strongly violated in model III and moderately in model V. If combined with our previous study on the angular distributions and with the data, our present study would indicate that only the standard bremsstrahlung mechanism could survive