Muonium-antimuonium oscillations in effective field theory

TL;DR

This paper investigates muonium-antimuonium oscillations as a potential probe for new physics beyond the standard model, using effective field theory to analyze the process and its sensitivity to lepton flavor violation.

Contribution

It provides a detailed effective field theory analysis of muonium-antimuonium oscillations and establishes constraints on new physics scales from these processes.

Findings

Invisible decays dominate the lifetime difference

Constraints on new physics scales are derived from oscillation data

Effective operators can probe BSM physics beyond other LFV processes

Abstract

Flavor violating processes in the lepton sector have highly suppressed branching ratios in the standard model mainly due to the tiny neutrino mass. This means that observing lepton flavor violation (LFV) in the next round of experiments would constitute a clear indication of physics beyond the standard model (BSM). We revisit a discussion of one possible way to search for LFV, muonium-antimuonium oscillations. This process violates muon lepton number by two units and could be sensitive to the types of BSM physics that are not probed by other types of LFV processes. Using techniques of effective field theory, we calculate the mass and width differences of the mass eigenstates of muonium. We argue that its invisible decays give the parametrically leading contribution to the lifetime difference and put constraints on the scales of new physics probed by effective operators in muonium oscillations.