FCNC Processes in the Littlest Higgs Model with T-Parity: an Update

Abstract

We update our 2006-2007 results for FCNC processes in the Littlest Higgs model with T-parity (LHT). The removal of the logarithmic UV cutoff dependence in our previous results through a new contribution to the Z 0 -penguin diagrams identified by Goto et al. and del Aguila et al., while making the deviations from the SM expectations in the quark sector less spectacular, still allows for sizable new physics effects in K → πν ν and K L → π 0 + − decays and in the CP-asymmetry S ψφ with the latter unaffected by the new contribution. We extend our analysis by a study of the fine-tuning required to fit the data on ε K and by the inclusion of the decay K L → µ + µ − . A number of correlations can distinguish this model from the custodially protected Randall-Sundrum model analysed recently. We also reconsider lepton flavour violating decays, including now a discussion of finetuning. While the i → j γ decays are unaffected by the removal of the logarithmic cutoff dependence, the branching ratios for decays with three leptons in the final state, like µ → 3e are lowered by almost an order of magnitude. In spite of this, the pattern of lepton flavour violation in the LHT model can still be distinguished from the one in supersymmetric models.

μ − e conversion in the Littlest Higgs model with T-parity

“…This complements our previous calculations of µ → eγ and µ → eee in [24] and those in [23,25]. The results for the Ti nucleus are in good agreement with previous work [23,26] where a degenerate mirror quark sector was assumed. Here we have also considered the effect of a more general quark sector where we include non-degenerate mirror quark masses and arbitrary mixings.…”

“…Here we have also considered the effect of a more general quark sector where we include non-degenerate mirror quark masses and arbitrary mixings. We have also found that µ N → e N is one-loop finite [24,26,27]. This is apparent for box diagrams but not for Z penguins.…”

“…The key observation is that the rates for the three processes, µ → eγ, µ → eee and µ N → e N, in general do not simultaneously vanish for any of the values of the parameters making it impossible for the model to fit into those areas. Scanning over parameter space has been discussed in some detail previously [23,26], finding large correlations for non-vanishing cross-sections between different processes. Here we prefer to look for the parameter regions where all processes get small, fulfilling all experimental constraints.…”

“…We present below the relation of the form factors for µ → eγ, µ → eee and µ N → e N used in this and our previous work [24], which follow from [40,49], with those introduced by Buras et al [23,36] corrected in [26]:…”

Complete next-to-leading order gluino contributions to and

“…Constraints within various supersymmetric extensions are analyzed in [20][21][22][23][24][25][26][27][28][29][30][31] (for overviews see [3,35]). Bounds on the Little Higgs Model with T-parity have also been presented [36]. Finally, model-independent analyses in the effective field theory approach without [37] and with the assumption of minimal flavor violation [10,11] also show the strong constraining power of the B → X s γ branching fraction.…”