A complete discussion of tree-level flavor-changing effects in the Randall-Sundrum (RS) model with brane-localized Higgs sector and bulk gauge and matter fields is presented. The bulk equations of motion for the gauge and fermion fields, supplemented by boundary conditions taking into account the couplings to the Higgs sector, are solved exactly. For gauge fields the Kaluza-Klein (KK) decomposition is performed in a covariant R ξ gauge. For fermions the mixing between different generations is included in a completely general way. The hierarchies observed in the fermion spectrum and the quark mixing matrix are explained naturally in terms of anarchic five-dimensional Yukawa matrices and wave-function overlap integrals. Detailed studies of the flavor-changing couplings of the Higgs boson and of gauge bosons and their KK excitations are performed, including in particular the couplings of the standard W ± and Z 0 bosons. A careful analysis of electroweak precision observables including the S and T parameters and the Z 0 bb couplings shows that the simplest RS model containing only Standard Model particles and their KK excitations is consistent with all experimental bounds for a KK scale as low as a few TeV, if one allows for a heavy Higgs boson (m h 1 TeV) and/or for an ultra-violet cutoff below the Planck scale. The study of flavor-changing effects includes analyses of the non-unitarity of the quark mixing matrix, anomalous righthanded couplings of the W ± bosons, tree-level flavor-changing neutral current couplings of the Z 0 and Higgs bosons, the rare decays t → c(u)Z 0 and t → c(u)h, and the flavor mixing among KK fermions. The results obtained in this work form the basis for general calculations of flavor-changing processes in the RS model and its extensions. arXiv:0807.4937v3 [hep-ph] 20 Oct 2008remaining issue of excessive contributions to the T parameter can be cured, e.g., by extending the bulk hypercharge group to SU (2) R × U (1) X and breaking it to U (1) Y on the UV brane [33]. An embedding of the SM fermions into the custodially symmetric SU (2) L × SU (2) R model, under which the left-handed bottom quark is symmetric under the exchange of SU (2) L and SU (2) R , allows one to protect the left-handed Z 0 bb coupling from vast corrections [34].Delocalized fermions have the further virtue of admitting a natural explanation of the flavor structure of the SM by harnessing the idea of split fermions [35]. In fact, it is perhaps not an overstatement to say that the RS scenario offers the best theory of flavor we have to date. Starting from anarchic 5D Yukawa couplings, the large mass hierarchies of the SM fermions can be generated without flavor symmetries by localizing the SM fermions at different points in the fifth dimension [21,26,36,37]. Given the large hierarchy of quark masses in the SM, small mixing angles in the Cabibbo-Kobayashi-Maskawa (CKM) matrix are a natural consequence of this scenario [37]. This way of generating fermion mass hierarchies also implies a certain amount of suppression of dangero...
We reexamine the Randall-Sundrum (RS) model with enlarged gauge symmetry SU (2) L × SU (2) R × U (1) X × P LR in the presence of a brane-localized Higgs sector. In contrast to the existing literature, we perform the Kaluza-Klein (KK) decomposition within the mass basis, which avoids the truncation of the KK towers. Expanding the low-energy spectrum as well as the gauge couplings in powers of the Higgs vacuum expectation value, we obtain analytic formulas which allow for a deep understanding of the model-specific protection mechanisms of the T parameter and the left-handed Z-boson couplings. In particular, in the latter case we explain which contributions escape protection and identify them with the irreducible sources of P LR symmetry breaking. We furthermore show explicitly that no protection mechanism is present in the charged-current sector confirming existing model-independent findings. The main focus of the phenomenological part of our work is a detailed discussion of Higgs-boson couplings and their impact on physics at the CERN Large Hadron Collider. For the first time, a complete one-loop calculation of all relevant Higgs-boson production and decay channels is presented, incorporating the effects stemming from the extended electroweak gauge-boson and fermion sectors.
A comprehensive analysis of tree-level weak interaction processes at low energy is presented for the Randall-Sundrum (RS) model with SU (2) L × U (1) Y bulk gauge symmetry and brane-localized Higgs sector. The complete form of the effective weak Hamiltonian is obtained, which results from tree-level exchange of Kaluza-Klein (KK) gluons and photons, the W ± and Z 0 bosons and their KK excitations, as well as the Higgs boson. Exact expressions are used for the bulk profiles of the various fields, and for the exchange of entire towers of KK gauge-boson states. A detailed phenomenological analysis is performed for potential new-physics effects in neutral-meson mixing and in rare decays of kaons and B mesons, including both inclusive and exclusive processes. We find that while the predictions for ∆F = 2 observables are rather model-independent, ∆F = 1 processes depend sensitively on the exact realizations of the electroweak gauge and the fermionic sector. In this context, we emphasize that the localization of the right-handed top quark in the extra dimension plays a crucial role in the case of rare Z 0 -mediated decays, as it determines the relative size of left-to right-handed couplings. We also extend earlier studies of quark flavor-changing neutral currents by examining observables which up to now attracted little attention. These include D-D mixing, B → τ ν τ , B → X s (Of special interest are the dimension-six operators describing the effective four-fermion interactions at low energies induced by heavy gauge-boson exchange. In particular, these will give rise to ∆F = 2 and ∆F = 1 FCNC processes, which are loop-suppressed in the SM. In the RS model, such processes arise already at tree level. However, as mentioned earlier, they are protected by the RS-GIM mechanism.( ). It follows that the latter ones can be discarded to very good approximation, whereas the contributions from the δ A matrices must only be kept to first order in v 2 /M 2 KK . We then obtain the simpler expression
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