Muon collider probes of Majorana neutrino dipole moments and masses

Majorana neutrinos may have transitional dipole moments, which violate leptonnumber as well as lepton flavour. We estimate the sensitivity of future colliders to the electron-muon neutrino dipole moment,lambda e mu, by considering same-sign dilepton final states.We find that hadron colliders, even the proposed FCC-hh, are sensitive only to|lambda e mu|greater than or similar to 10-9 mu B(with mu B the Bohr magneton), a value two-three orders of magnitude larger than currentbounds from astrophysics and low-energy neutrino-scattering experiments. In the case of afuture muon collider, we show that the sensitivity varies from|lambda e mu|similar to 5<middle dot>10-9 mu Bfor energy root s similar or equal to 3TeV, to similar to 10-12 mu Bfor root s similar or equal to 50TeV, matching the current laboratory bounds for root s similar or equal to 30TeV. The singular advantage of the muon collider signal would be a direct, clean identification of lepton number and flavour violation. We also show that a muon collider would improve by orders of magnitude the direct bounds on me mu and m mu mu, two of the entriesof the Majorana neutrino mass matrix. These bounds could be as strong as similar to 50keV, stillfar above the neutrino mass scale