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−ν̄τ, 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−ν̄τ) = (1.79−0.49+0.56(stat)−0.46+0.39(syst)) × 10−4.