2009/05/31 by Andrzej J. Buras, Andrzej J Buras, Bjoern Duling +2
Physics and Astronomy · #Boson #Coupling (piping) #Fermion #Gauge boson #Higgs boson #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #Quark #Standard Model (mathematical formulation) #hep-ph
paper · pdf · doi:10.1088/1126-6708/2009/09/076
published as JHEP 0909:076,2009 · 40 pages, 8 figures. Comments added, references added, typos corrected
openalex publication_date 2009/09/15 · arxiv created 2009/12/11 · arxiv updated 2010/01/07 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 ZdLi dLi and flavour violating ZdLi dLj couplings. We point out that in this model also the couplings of ZuRi uRi and ZuRi uRj 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 PLR 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 ZH 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(v2/MKK2) 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 3x3 matrix that describes the pattern of flavour violation in these new interactions of the standard W.