Lepton flavor violation in the standard model extended by heavy singlet neutrinos

Some properties of extensions of standard model (SM) by heavy neutrinos with large lepton flavor violation (LFV) effects are given. The possible low energy processes and methods, which could show deviation from the SM in the neutrino sector, are mentioned. The low energy neutrinos LFV decays are listed. The amplitudes contributing to LFV decays and behaviour of total amplitudes in the large mass limit are given. Some interesting ratios of branching ratios are mentioned. The perturbative unitarity limit for heavy neutrino masses is discussed. The theoretical upper limits of branching ratios (BRs) are compared with the current experimental upper bounds and several choices of model parameters to fit the experimental results are evaluated. Astrophysical constraints on mixing angles are discussed