Production of the massless dark photon $\widetilde{\gamma}$ associated with the photon $\gamma$ from charged lepton flavor violating decay processes

Abstract

Abstract The massless dark photon $\widetilde{\gamma}$ can only interact with Standard Model (SM) sector via higher-dimensional operators. In this letter, we investigate its production associated with the ordinary photon $\gamma$ from the lepton flavor violation (LFV) process $\ell_i\rightarrow\ell_j\widetilde{\gamma}\gamma$ and di-production from the LFV process $\ell_i\rightarrow\ell_j \widetilde{\gamma} \widetilde{\gamma}$ induced by dipole operators. Comparing the obtained numerical results with the corresponding experimental measurements, we obtain the constraints on the effective couplings of $\widetilde{\gamma}$ with the SM charged leptons. The upper limit of the effective coupling ${\left|D_L^{\mu e}\right|}^2+{\left|D_R^{\mu e}\right|}^2$ coming from the process $\mu \rightarrow e\widetilde{\gamma}\gamma$ is looser than the process $\mu \rightarrow e\widetilde{\gamma}$ by about one order of magnitude.