ΔF= 2 observables and fine-tuning in a warped extra dimension with custodial protection

Abstract

We present a complete study of ∆S = 2 and ∆B = 2 processes in a warped extra dimensional model with a custodial protection of Zb LbL , including ε K , ∆M K , ∆M s , ∆M d , A q SL , ∆Γ q , A CP (B d → ψK S ) and A CP (B s → ψφ). These processes are affected by tree level contributions from Kaluza-Klein gluons, the heavy KK photon, new heavy electroweak gauge bosons Z H and Z ′ , and in principle by tree level Z contributions. We confirm recent findings that the fully anarchic approach where all the hierarchies in quark masses and weak mixing angles are geometrically explained seems implausible and we confirm that the KK mass scale M KK generically has to be at least ∼ 20 TeV to satisfy the ε K constraint. We point out, however, that there exist regions in parameter space with only modest fine-tuning in the 5D Yukawa couplings which satisfy all existing ∆F = 2 and electroweak precision constraints for scales M KK ≃ 3 TeV in reach of the LHC. Simultaneously we find that A CP (B s → ψφ) and A s SL can be much larger than in the SM as indicated by recent results from CDF and DØ data. We point out that for B d,s physics ∆F = 2 observables the complex (Z H , Z ′ ) can compete with KK gluons, while the tree level Z and KK photon contributions are very small. In particular we point out that the Zd i Ld j L couplings are protected by the custodial symmetry. As a by-product we show the relation of the RS flavour model to the Froggatt-Nielsen mechanism and we provide analytic formulae for the effective flavour mixing matrices in terms of the fundamental 5D parameters.

FCNC effects in a minimal theory of fermion masses

“…It is remarkable that already the minimal FCNC effects that we are studying here give quite stringent bounds at least on M D , not much weaker than the typical constraints on the compositeness/KK scale one finds in complete models [22,[33][34][35][36][37]. On the other hand, the bounds on M Q,U,D do not exclude the possibility that some of the heavy fermions could be as light as a TeV.…”

Strong signatures of right-handed compositeness

“…These scenarios are in fact strongly motivated by flavor physics. Assuming universal couplings for either left-handed or right-handed fermions allows to realize the hypothesis of Minimal Flavor Violation (MFV) [18] in strongly coupled theories, solving the flavor problem of composite Higgs models [14][15][16][17]. Here the compositeness of the up quark cannot be small, it being determined by the one of the top.…”

LHC predictions from a tevatron anomaly in the top quark forward-backward asymmetry

“…[41] which contains a very similar set-up. The procedure is, essentially, as follows: (i) draw the contributing diagrams arising from L FCNC and integrate G out.…”