Lepton-flavor violation in the supersymmetric standard model with seesaw-induced neutrino masses

Abstract

We examine the lepton-flavor violation caused by a Yukawa coupling matrix y ν,ij for right-handed neutrinos in the supersymmetric standard model. We stress that decay rates for τ → µγ and µ → eγ may reach the range to be accessible to near future experiments if left-right mixing terms in the slepton mass matrix are substantially large.

The see-saw mechanism, neutrino Yukawa couplings, LFV decays li→lj+γ and leptogenesis

“…As was indicated in the Introduction, in the class of theories we consider, one of the effects of RG running from M X to M R < M X is the generation of new contributions in the amplitudes of the LFV processes [20,22]. In the "mass insertion" and leading-log approximations (see, e.g., [22,24,28]), the branching ratio of l i → l j + γ decay due to the new contributions has the following form…”

“…In the "mass insertion" and leading-log approximations (see, e.g., [22,24,28]), the branching ratio of l i → l j + γ decay due to the new contributions has the following form…”

“…If the SUSY breaking occurs via soft terms with universal boundary conditions at a scale M X above the RH Majorana neutrino mass scale M R , M X > M R 2 , the renormalisation group (RG) effects transmit the LFV from the neutrino mixing at M X to the effective mass terms of the scalar leptons at M R even if the soft SUSY breaking terms at M X are flavour symmetric and conserve the lepton charges L l . As a consequence of these RG-induced new LFV terms in the effective Lagrangian at M R < M X , the LFV processes can proceed with rates and cross sections which are within the sensitivity of presently operating and future planned experiments [20,22] (see also, e.g., [23,24,25,26,27,28,29,30]). In contrast, in the non-supersymmetric case, the rates and cross sections of the LFV processes are suppressed by the factor [31] (see also [32]) (m j /M W ) 4 < 6.7 × 10 −43 , M W being the W ± mass, which renders them unobservable.…”

Light charged Higgs at the beginning of the LHC era

“…Unfortunately these decays require an additional source of LFV. However, LFV couplings naturally appear in the MSSM once we extend it to accommodate the non-vanishing neutrino masses and mixing angles by means of a supersymmetric seesaw mechanism [72,73]. In this case, LFV entries in the slepton mass matrix (m 2 L ) ij are radiatively induced [72]:…”

Search for the lepton number violating decay τ → μγ

“…The decay τ → µγ is an anticipated lepton-number violating process in supersymmetric models [1,2,3], left-right supersymmetric models [4] and in supersymmetric string unified models [5]. For some ranges of model parameters, decay rates as high several parts per million are expected for this decay [3,5], even in light of the current experimental limit on the related µ → eγ decay [6].…”