Top quark Kaluza-Klein mode mixing in the Randall-Sundrum bulk standard model and B→X_sγ

We study top quark Kaluza-Klein (KK) mode mixing in the Randall-Sundrum scenario with all the SM fermions and gauge bosons in the bulk. Even though the simple assumption of a universal bulk fermion mass m_ψ leads to the same KK mass spectrum for all SM fermions and thus suppresses new contributions to the flavor changing neutral current and the ρ parameter, the large Yukawa coupling of the top quark generates mixing among its KK modes and breaks the degeneracy: An unacceptably large contribution to Δρ occurs. In order to satisfy the Δρ constraint, we relax the model by assigning a different bulk fermion mass to the SU(2) singlet bottom quark and demonstrate that there exists some limited parameter space where the Δρ constraint is satisfied. It is also shown that the current measurement of Br(B→X_s+γ) can be accommodated in this modified model, and the one sigma level precision constrains the effective weak scale k_EW such as k_EW ≳3. TeV for mψ/k= -0.4, where k_EW is the warp-suppressed AdS₅ curvature.