Access Type

Open Access Dissertation

Date of Award

January 2022

Degree Type


Degree Name



Physics and Astronomy

First Advisor

Alexey Petrov


The Standard Model is believed to be a low energy effective theory of some completetheory at higher energies. This is already evidenced in the observation of neutrino oscillations. Standard Model processes conserve the lepton flavor quantum numbers. Adding massive neutrinos to the Standard Model, the branching ratios of lepton flavor violating processes are found to be incredibly small. For example, a process μ → eγ has a branching ratio order ∼ 10^−54. These tiny branching ratios of lepton flavor violating processes indicate that they are especially clean areas to look for beyond the Standard Model physics. Any observed flavor violation would be new physics, and this has motivated searches for μ → eγ and μ → eee processes in muon experiments such as MEG and SINDRUM. These experiments have produced bounds on the branching ratios of these processes, already probing new physics at the scales of LHC experiments. Upcoming experiments such as MEG II and Mu3e should improve the current bounds by several orders of magnitude. Working in an effective field theory framework, we can use these experimental bounds to put constraints on the parameters of new physics models, such as the scale Λ at which new physics becomes operative. In this thesis, we examine the probabilities of the lepton flavor violating processes of the muonium atom. We compute the mass and, for the first time, the width difference of the mass eigenstates on muonium-antimuonium oscillations. Using the calculated mass and width difference, we use the current experimental bounds on muonium-antimuonium oscillations to put constraints on the new physics scale Λ. We also consider lepton-flavor violating two-body decays of muonium into two-lepton and two-photon states. The two-body muonium decays have a simpler experimental signature, and the corresponding Wilson coefficients can be restricted better in the muonium case. We argue that experimental searches for lepton flavor violating decays of muonia could be more advantageous than lepton flavor violating muon decays in some cases.

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