Muonium-antimuonium oscillations in an extended minimal supersymmetric standard model with right-handed neutrinos

Boyang Liu, Purdue University

Abstract

The electron and muon number violating muonium-antimuonium oscillation process in two different models is investigated. First, modifying the Standard Model only by the inclusion of singlet right-handed neutrinos and allowing for general renormalizable interactions producing neutrino masses and mixing, the leading order matrix element contribution to this process is computed in Rξ gauge thereby establishing the gauge invariance to this order. To give a natural explanation of the smallness of the observed neutrino masses, the see-saw mechanism is explored resulting in three light Majorana neutrinos and three heavy Majorana neutrinos with mass scale MR >> MW. Present experimental limits set by the nonobservation of the oscillation process sets a lower limit on MR of roughly of order 600 GeV. Second, modifying the Minimal Supersymmetric Standard Model by the inclusion of three right-handed neutrino superfields and allowing only intra-generation lepton number violation but not inter-generation lepton number mixing, the muonium-antimuonium conversion can occur while the process μ → eγ is forbidden. For a wide range of the parameters, the contributions to the muonium-antimuonium oscillation time scale are at least two orders of magnitude below the sensitivity of current experiments. However, if the ratio of the two Higgs field VEVs, tan β, is very small, there is a limited possibility that the contributions are large enough for the present experimental limit to provide an inequality relating tan β with the light neutrino mass scale mv which is generated by see-saw mechanism. The resultant lower bound on tan β as a function of mv is more stringent than the analogous bounds arising from the muon and electron anomalous magnetic moments as computed using this model.

Degree

Ph.D.

Advisors

Love, Purdue University.

Subject Area

Particle physics

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