LEPTON NUMBER VIOLATION DECAYS IN E6 STRING MODEL

Lepton number violation decays l(i) --> l(j)gammagamma and l(j) --> 3l (j) are investigated in the framework of E6 superstring model and the explicit expression for these decay rates are obtained. Relations betw een lepton number violation decays l(i) --> l(j)gammagamma and l(i) -- > l(j)gamma are established and it is shown that the relative value of these decays is independent of the details of the considered model. I n the considered model we predict that BR(tau --> mugammagamma) is lar ge than BR(mu --> egamma) in spite of the fact that tau --> mugammagam ma decay is suppressed by a factor of alpha(el)/pi, compared to the mu --> --> egamma. Using the present experimental restrictions, the uppe r bound for tau --> mugammagamma decays and lower limits for the masse s of new particles are obtained. Also it is shown that rare mu --> 3e decay has large BR in comparison with tau --> 3mu and tau --> 3e decay s.