Lepton Flavor Violating τ and Leptonic B Decays at B-factories

We would like to review recent searches for lepton flavor violation (LFV) in τ decays carried out at the KEKB and PEPII B-factories. No evidence for such decays has been found yet and upper limits for various decay modes were obtained. The sensitivity to branching fractions of LFV decays is approaching ∼ 10-8, of which new physics beyond the Standard model is anticipated to possibly appear. Beside, Belle collaboration just presents the first evidence of a pure leptonic B decay B- → τ-ν(bar sign)τ, using 414 fb-1 of data. They detect the signal with a significance of 3.5 standard deviations including systematics, and measure the branching fraction to be B(B- → τ-ν(bar sign)τ) (1.79-0.49+0.56(stat)-0.46+0.39(syst)) x 10-4