Rare and forbidden B and tau decays in the Belle

A search for the purely leptonic decays B⁺ → e⁺v_e and B⁺ → μ⁺v_μ was performed using the 772 million B B-bar pairs collected by the Belle detector at the KEKB asymmetric-energy e⁺e⁻ collider. There was no evidence of a signal in either decay modes. A heavy neutral leptonlike new particle and heavy neutrino searches were also performed, but no significant signals were observed. Lepton flavor violation in τ decays was studied with an almost full data sample and the upper limits obtained were in the order of 10⁻⁸. In this paper, recent results that can give any constraints to new physics are briefly described