Indirect upper limits on ℓi →ℓjγγ from ℓi →ℓjγ

Abstract

We perform an effective field theory analysis to correlate the charged lepton flavor violating processes li → ljγγ and li → ljγ. Using the current upper bounds on the rate for li → ljγ, we derive modelindependent upper limits on the rates for li → ljγγ. Our indirect limits are about three orders of magnitude stronger than the direct bounds from current searches for μ → eγγ, and four orders of magnitude better than current bounds for τ → lγγ. We also stress the relevance of Belle II or a Super Tau Charm Facility to discover the rare decay τ → lγγ