We investigate an invisible lepton-flavor-violating scalar $\phi$ with exclusive $e-\mu$ couplings and study its resonant production via $\mu^+e^-\to\phi$ in fixed-target experiments. Since the effective center-of-mass energy is determined by the momentum of the initial-state bound electrons, atomic effects can significantly affect the resonance behavior. We therefore employ relativistic bound-state electron wave functions to calculate the production cross section and reveal a material-dependent broadening of the resonance lineshape. For the proposed HIAF experiment, fewer than one day of data taking ($6\times10^{10}$ MOT) can probe couplings at the $10^{-5}$ level at 90\% confidence level near resonance, demonstrating that high-intensity muon fixed-target experiments provide a powerful complementary probe of lepton-flavor violation.
Purely leptonic bound states provide precision probes of QED. Positronium $(e^+e^-)$ and muonium $(\mu^+e^-)$ have long been observed, whereas dimuonium $(\mu^+\mu^-)$ and tauonium $(\tau^+\tau^-)$ remain undiscovered. We study exclusive vector-leptonium electroproduction in $ep$ collisions within nonrelativistic QED....
Hao K. Deng, Qi-Ming Feng, Qi-Wei Hu et al.· 0 citations
We investigate the sensitivity of a same-sign $\mu^+\mu^+$ collider to doubly charged scalars in the Type-II seesaw framework, focusing on the regime in which the doubly charged scalar decays dominantly into same-sign $W$-boson pairs. Motivated by the $\mu$TRISTAN proposal, for a benchmark we consider a degenerate trip...
Mariana Frank, B. Fuks, Chayan Majumdar et al.· 0 citations
We investigate the potential of high-intensity muon experiments such as MEG~II and Mu3e to uncover dark matter (DM) through the lepton-flavor-violating decay $\mu^+\to e^+\chi\bar\chi$. We describe the underlying interactions in terms of dimension-six four-fermion operators and systematically explore all allowed Lorent...
D. Barducci, Giulio Marino, P. Panci et al.· 0 citations
We investigate the sensitivity of DUNE-like facilities to flavor-changing neutral-current interactions between down and strange quarks through inclusive deep-inelastic neutrino scattering. In the framework of a general low-energy effective Lagrangian for Dirac and Majorana neutrinos, we evaluate projected sensitivities...
Xin-Shuai Yan, Miao Liu, Qin Chang et al.· 0 citations
We construct a non-relativistic Lagrangian that describes muon-proton electroweak interactions. We determine the leading order coefficients by matching onto the theory with non-relativistic nucleons and relativistic leptons. The most impactful $\mathcal{O}(\alpha)$ corrections to those coefficients are determined by ma...
Evan Combes, E. Mereghetti, L. Platter· 0 citations
We combine the current experimental muon $g-2$ world average, which incorporates the final Fermilab result, with the latest electron $g-2$ determinations based on cesium and rubidium measurements to set 95\% CL exclusion contours for a pure vector mediator coupled to leptons. We explicitly test the assumption that the...
R. Serao, A. Capolupo· 0 citations
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