We present the electroweak and flavour structure of a model with a warped extra dimension and the bulk gauge group SU (3) c × SU (2) L × SU (2) R × P LR × U (1) X . The presence of SU (2) R implies an unbroken custodial symmetry in the Higgs system allowing to eliminate large contributions to the T parameter, whereas the P LR symmetry and the enlarged fermion representations provide a custodial symmetry for flavour diagonal and flavour changing couplings of the SM Z boson to left-handed down-type quarks. We diagonalise analytically the mass matrices of charged and neutral gauge bosons including the first KK modes. We present the mass matrices for quarks including heavy KK modes and discuss the neutral and charged currents involving light and heavy fields. We give the corresponding complete set of Feynman rules in the unitary gauge.

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.

No abstract

We reconsider the impact of heavy vector-like fermions on the couplings of standard model (SM) quarks to the SM gauge bosons W ± and Z and to the SM Higgs boson H. Integrating out these fermions at tree level we derive general formulae that can be used in any model containing such particles. We apply these formulae to the case of the lightest Kaluza-Klein (KK) fermions in a Randall-Sundrum (RS) model with a custodial protection of flavour conserving Zd i Ld i L and flavour violating Zd i Ld j L couplings. We point out that in this model also the couplings of Zu i Rū i R and Zu i Rū j R are protected.In particular we demonstrate explicitly that this protection is not spoiled by the mixing of the SM quarks with the KK fermions, which is guaranteed by the underlying P LR symmetry. We find that the impact of KK fermions on the Z-couplings, while not negligible, is significantly smaller than the one coming from the mixing of Z with the heavy KK gauge bosons Z H and Z ′ . The situation is similar for the W ± couplings with the only exception of the tb coupling where the impact of KK fermions can in principle be larger than the effects that are induced by gauge boson mixing. We also show explicitly that at O(v 2 /M 2 KK ) the fermion-Higgs couplings of a Higgs placed on the infrared (IR) brane is not affected by the KK contributions up to strongly chirally suppressed contributions. The corrections to the CKM matrix, in particular the breakdown of its unitarity, are found to be small. We also investigate the right-handed couplings of W ± that are generated through the mixing with KK-fermions and introduce a 3×3 matrix that describes the pattern of flavour violation in these new interactions of the standard W ± .

After a brief theoretical introduction of the warped extra-dimensional model with custodial protection the results of [1] are presented. In this work we analyze the impact of Kaluza-Klein (KK) gauge boson modes on ∆F = 2 observables, for the first time considering the full operator basis and including NLO renormalization group running. It is pointed out that the dominant contribution in the B-system does not come from the KK gluon, but that contributions from KK excitations of the weak gauge bosons are competitive. In a numerical analysis we assess the amount of fine-tuning necessary for obtaining realistic values for quark masses and mixings and at the same time realistic values for ǫK , the measure for CP violation in K meson mixing. We are able to show that a mass of the lightest KK gauge boson of 2-3 TeV, and hence in the reach of the LHC, is still possible for moderate fine-tuning. These results enable us to make predictions for not yet measured ∆F = 2 observables, such as S ψφ and A SL s , which can differ significantly from their SM values.