Top quark Kaluza-Klein mode mixing in the Randall-Sundrum bulk standard model andB→Xsγ

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 $m_{\psi }$ leads to the same KK mass spectrum for all SM fermions and thus suppresses new contributions to the flavor changing neutral current and the $\rho$ parameter, the large Yukawa coupling of the top quark generates mixing among its KK modes and breaks the degeneracy: An unacceptably large contribution to $\Delta \rho$ occurs. In order to satisfy the $\Delta \rho$ 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 $\Delta \rho$ constraint is satisfied. It is also shown that the current measurement of $\mathrm{Br}(\overrightarrow{B}{X}_s+\gamma )$ can be accommodated in this modified model, and the one sigma level precision constrains the effective weak scale $k_{\mathrm{EW}}$ such as $k_{\mathrm{EW}}\gtrsim 3\mathrm{TeV}$ for $m_{\psi }/k=-0.4,$ where $k_{\mathrm{EW}}$ is the warp-suppressed ${\mathrm{AdS}}_5$ curvature.