5D UED: flat and flavorless

Abstract

Abstract5D UED is not automatically minimally flavor violating. This is due to flavor asymmetric counter-terms required on the branes. Additionally, there are likely to be higher dimensional operators which directly contribute to flavor observables. We document a mostly unsuccessful attempt at utilizing localization in a flat extra dimension to resolve these flavor constraints while maintaining KK-parity as a good quantum number. It is unsuccessful insofar as we seem to be forced to add brane operators in such a way as to precisely mimic the effects of a double throat warped extra dimension. In the course of our efforts, we encounter and present solutions to a problem common to many extra dimensional models in which fields are "doubly localized:" ultra-light modes. Under scrutiny, this issue seems tied to an intrinsic tension between maintaining Kaluza-Klein parity and resolving mass hierarchies via localization.

A review on non-minimal universal extra dimensions

“…[33] to be R −1 ∼ > 600 GeV. Generic non-minimal extensions by boundary terms or quark bulk masses can induce FCNCs at the tree-level, which are highly constrained due to the absence of an RS-GIM mechanism [2]. Hence boundary terms and bulk masses in the fermion sector are typically assumed to be flavor-blind (cf.…”

“…quarks, leptons, gauge bosons and the Higgs boson which have been observed at the LHC. If the extra dimension is 'symmetric' under the reflection about its midpoint, which may be regarded as the consequence of two throats compactification [2] as shown in Fig. 1, a KK mode carries a definite parity (even or odd), dubbed KK-parity.…”

Black holes and the LHC: A review

“…The splitting is a unique phenomenon in extra dimension models and it may be responsible for the observed Yukawa hierarchy [135] (also see [136,137] for universal extra dimension (UED) setup) and the proton longevity problem (Adams (2000) [139]) in particle physics.…”

Constraints on universal extra dimensions fromW′searches

“…4 In Ref [21] it has been shown that fermion mass matrices in split-UED induce FCNC's unless the mass matrices are flavor blind, i.e., proportional to the unit matrix in flavor space. The same arguments hold for fermion BLKTs.…”