Lepton Flavor Violation from diphoton effective interactions

Abstract

We consider charged lepton flavor violating transitions mediated by the diphoton effective interactions ${\ell }_i{\ell }_j\gamma \gamma$ and explore which processes can probe them better. Our analysis includes single and double radiative decays, ${\ell }_i\to {\ell }_j\gamma (\gamma )$, as well as ${\ell }_i\to {\ell }_j$ conversions in nuclei for all possible flavor combinations, which we compute for the first time for $\ell \to \tau$ conversions in this framework. We find that currently the best limits are provided by the loop-induced ${\ell }_i\to {\ell }_j\gamma$ processes, while the best future sensitivities come from $\mu \to e$ conversion in aluminum and from potential $\tau \to \ell \gamma \gamma$ searches at Belle II or at the Super Tau Charm Facility. We also motivate the search for $\mu \to e\gamma \gamma$ at the Mu3e experiment as a complementary probe of these operators.

Comments: 11+6 pages, 4 figures. Extended discussion. Matches published version