[hep-ph/0302186] Lepton-flavor-violating decays L->l gamma gamma as a new probe of supersymmetry with broken R-parity

Lepton-flavor-violating decays of the type L->l gamma gamma (mu->e gamma gamma, tau->e gamma gamma, and tau->mu gamma gamma) are proposed as new probes of R-parity-violating supersymmetry. Non-penguin diagrams with a sneutrino that decays into two photons via a triangle graph might trigger such decays even in the absence of the corresponding radiative decays into one photon only, e.g. mu->e gamma. Thus, processes of the type L->l gamma gamma may provide an independent probe of new flavor physics.

よく調べられてきたのはmu->e gammaとかtau -> mu/e gammaだったのだけれど、ell gamma gammaも結構いけるみたい。