Abstract

We propose a realization of Minimal Flavor Violation in the lepton sector of the Randall–Sundrum model. With the MFV assumption, the only source of flavor violation are the 5D Yukawa couplings, and the usual two independent sources of flavor violation are related. In the limit of massless neutrinos, the bulk mass matrices and 5D Yukawa matrices are simultaneously diagonalized, and hence the absence of FCNCs. In the case of massive neutrinos, the contributions to FCNCs in the charged lepton sector are highly suppressed, due to the smallness of neutrino masses. In addition, the MFV assumption also allows suppressing one-loop charged current contributions to flavor changing processes by reducing the size of the Yukawa couplings, which is not possible in the generic anarchical case. We found that the first KK mass scale as low as ∼3 TeV can be allowed. In both cases, we present a set of numerical results that give rise to realistic lepton masses and mixing angles. Mild hierarchy in the 5D Yukawa matrix of O(25) in our numerical example is required to be consistent with two large and one small mixing angles. This tuning could be improved by having a more thorough search of the parameter space.

Highlights

  • The Randall-Sundrum (RS) model [1] is a solution to the gauge hierarchy problem based on non-factorizable geometry in a slice of AdS5 space with warped background metric

  • We propose a realization of Minimal Flavor Violation in the lepton sector of the Randall-Sundrum model

  • The non-diagonal term in Eq (6) is the source of the FCNCs in the charged lepton sector. Because this term is proportional to ξ, the size of the contributions to FCNCs is determined by the value of ξ, which turns out to be small in order to accommodate realistic lepton masses, as we show below

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Summary

INTRODUCTION

The Randall-Sundrum (RS) model [1] is a solution to the gauge hierarchy problem based on non-factorizable geometry in a slice of AdS5 space with warped background metric. There are two sources of flavor violation, the 5D Yukawa couplings and the bulk fermion mass terms, which can generate dangerous tree-level FCNCs mediated by the KK gauge bosons. Even though these processes are somewhat suppressed by the built-in RS GIM mechanism [8], constraints from the CP-violating parameter ǫK for Ko − Ko mixing still gives a stringent bound of 8 TeV with a generic flavor structure [9]. MFV alleviates the tension that exists in the generic anarchical case between the tree-level FCNCs and one-loop charged-current contributions to LFV processes. It allows the charged-current contributions to be suppressed by reducing the Yukawa couplings without increasing the tree-level FCNC contributions

MINIMAL FLAVOR VIOLATION IN THE LEPTON SECTOR
CONCLUSIONS
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