Finding the neutrino mass mechanism at muon colliders

Speaker(s) Kåre Fridell (KEK, Tsukuba)

In this talk I will show how neutrino mass mechanisms may be probed in future muon colliders, with special emphasis on the proposed μTRISTAN experiment. If neutrinos are Majorana particles, they may lead to charged lepton flavor violating processes that would constitute clear evidence for New Physics in the lepton sector. Using an effective field theory framework, we then compare the potential discovery reach with existing limits from rare lepton decays, finding that muon colliders are the most sensitive probe of charged lepton flavor violation for a range of parameters. As a model example, we then consider the type-ii seesaw model, and show how a muon collider could be used to constrain the CP-violating phases of the corresponding PMNS matrix.