1202.4906 (Jennifer Girrbach et al.)

Gamma(K -> e nu)/Gamma(K -> mu nu) in the Minimal Supersymmetric
Standard Model    [PDF]

Jennifer Girrbach, Ulrich Nierste

The quantity R_K = Gamma(K -> e nu)/Gamma(K -> mu nu) studied by the
experiment NA62 at CERN is known to probe lepton-flavour violating (LFV)
parameters of the Minimal Supersymmetric Standard Model (MSSM). A non-zero
parameter delta_{RR}^{13} can open the decay channel K -> e nu_tau and enhance
R_K over its Standard-Model value. In the region of the parameter space probed
by NA62 the contribution from a bino-stau loop diagram is numerically dominant
and the mixing between left-handed and right-handed staus is important. For
large values of the stau mixing angle theta_tau the commonly adopted mass
insertion approximation is not accurate. We therefore express the
supersymmetric contribution to R_K in terms of the mass of the lightest stau
eigenstate, the mixing angle theta_tau, and other relevant MSSM parameter such
as tan(beta) and the charged-Higgs boson mass M_H and plot the parameter
regions constrained by R_K. We further study to which extent R_K can be
depleted through MSSM contributions interfering destructively with the SM
amplitude for K -> e nu_e. This lepton-flavour conserving (LFC) mechanism
involves the parameter combination |delta_{LL}^{13} delta_{RR}^{13}|, which can
be constrained with a naturalness consideration for the electron mass or with
the measurement of the anomalous magnetic moment of the electron. The LFC
effect on R_K is marginal, an NA62 measurement of R_K significantly below the
Standard Model expectation would indicate physics beyond the MSSM.

View original: http://arxiv.org/abs/1202.4906