Higgs mediated flavor violating electromagnetic interactions, induced at the one-loop level by a nondiagonal $H{f}_i{f}_j$ vertex, with $f_i$ and $f_j$ charged leptons or quarks, are studied within the context of a completely general effective Yukawa sector that comprises $S{U}_L(2)\times U_Y(1)$-invariant operators of up to dimension-six. Exact formulae for the one-loop $\gamma f_i{f}_j$ and $\gamma \gamma f_i{f}_j$ couplings are presented and their related processes used to study the phenomena of Higgs mediated lepton flavor violation. The experimental limit on the $\mu \to e\gamma$ decay is used to derive a bound on the branching ratio of the $\mu \to e\gamma \gamma$ transition, which is 6 orders of magnitude stronger than the current experimental limit. Previous results on the $\tau \to \mu \gamma$ and $\tau \to \mu \gamma \gamma$ decays are reproduced. The possibility of detecting signals of lepton flavor violation at $\gamma \gamma$ colliders is explored through the $\gamma \gamma \to l_i{l}_j$ reaction, putting special emphasis on the $\tau \mu$ final state. Using the bound imposed on the $H\tau \mu$ vertex by the current experimental data on the muon anomalous magnetic moment, it is found that about half a hundred events may be produced in the International Linear Collider.

• Received 11 February 2009

DOI:https://doi.org/10.1103/PhysRevD.79.093009