This operator contains s and d fields of both chiralities. As a result, in a large class of split fermion models, the overlap suppression would be similar to that accounting for the smallness of the down and strange 4D Yukawa couplings. Integrating over the 5D profiles of the four quarks, this may yield a suppression factor of O ( m$_{d}$m$_{s}$/v 2 ) ∼ 10 − $^{9}$. Together with the naive scale suppression, 1 / Λ 2 $_{5D}$, the coefficient of O 4 K can be sufficiently suppressed to be consistent with the experimental bound. In the absence of large brane kinetic terms (BKTs), however, fermion localization generates order one non-universal couplings to the gauge KK fields [63]. (See e.g. [64] and references therein. The case with large BKTs is similar to the warped case discussed below.) The fact that the bulk masses are, generically, not aligned with the 5D Yukawa couplings implies that KK gluon exchange processes induce, among others, the following operator in the low energy theory: [ ( D$_{L}$ ) 2 $_{12}$/ (6 M 2 $_{KK}$) ] (¯ s$_{L}$ d$_{L}$ ) $^{2}$, where ( D$_{L}$ )$_{12}$ ∼ λ is the left-handed down-quark rotation matrix from the 5D interaction basis to the mass basis. This structure provides only a mild suppression to the resulting operator. It implies that to satisfy the ϵ$_{K}$ constraint the KK and the inverse compactifi- cation scales have to be above 10 $^{3}$TeV, beyond the direct reach of near future experiments, and too high to be linked to a solution of the hierarchy problem. This problem can be solved by tuning the 5D flavor parameters and imposing appropriate 5D flavor symmetries to make the tuning stable. Once the 5D bulk masses are aligned with the 5D Yukawa matrices the KK gauge contributions would vanish and such a configuration is radiatively stable. The warped extra-dimension [Randall-Sundrum (RS)] framework [65] provides a solution to the hierarchy problem. Moreover, with SM fermions propagating in the bulk, both the SM and the NP flavor puzzles can be addressed. The light fermions could be localized away from the TeV brane [66], where the Higgs is localized. Such a configuration can generate the observed Yukawa hierarchy and, at the same time, ensure that higher-dimensional operators are suppressed by a high cutoff scale associated with the location of the light fermions in the extra dimension [67]. Furthermore, since the KK states are localized near the TeV brane, the couplings between the SM quarks and the gauge KK fields exhibit the hierarchical structure associated with SM masses and CKM mixings. This hierarchy in the couplings provides an extra protection against non-standard flavor-violating effects [68] denoted as RS-GIM mechanism [69] (see also [70]). It is interesting to note that an analogous mechanism is at work in models with strong dynamics at the TeV scale, with large anomalous dimension and partial compositeness [71]. The link with strongly-interacting models in indeed motivated by the AdS/CFT correspondence [72], which implies that the above 5D framework is the dual description of 4D composite Higgs models [73]. 23