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