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

TL;DR

This paper updates the analysis of flavor-changing neutral current processes in the Littlest Higgs model with T-parity, incorporating new contributions that refine previous results and exploring implications for various rare decays and CP asymmetries.

Contribution

It introduces a new contribution to Z^0-penguin diagrams that removes UV cutoff dependence, providing a more accurate analysis of FCNC processes in the LHT model.

Findings

Deviations from the SM are less spectacular but still significant in certain rare decays.

The pattern of lepton flavor violation can distinguish the LHT model from supersymmetric models.

Branching ratios for some lepton decays are reduced by nearly an order of magnitude.

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 -> pi nu anti-nu and K_L -> pi^0 l^+ l^- decays and in the CP-asymmetry S_{psi phi} 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 epsilon_K and by the inclusion of the decay K_L -> mu^+ mu^-. 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 fine-tuning. While the l_i -> l_j gamma decays are unaffected by the removal of the logarithmic cutoff dependence, the branching ratios for decays with three leptons in the final state, like mu -> 3 e 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.