Flavor Violation in Theories with TeV Scale Quantum Gravity

Zurab Berezhiani; Gia Dvali

doi:10.1016/S0370-2693(99)00135-5

paper

Flavor Violation in Theories with TeV Scale Quantum Gravity

arXiv:hep-ph/9811378 · doi:10.1016/S0370-2693(99)00135-5

Abstract

We study the effects of possible flavor-violating operators in theories with the TeV scale quantum gravity, in which the ordinary matter is localized on a 3-brane embedded in the space with $N$ extra dimensions, whereas gravity propagates in the bulk. These operators are scaled by the fundamental Planck mass $M_{P f} \sim$ TeV and must be suppressed by the gauge family symmetries. We study suppression of the most dangerous and model-independent operators. Several points emerge. First, we show that the Abelian symmetries can not do the job and one has to invoke non-Abelian $U (2)_{F}$ (or $U (3)_{F}$ ) symmetries. However, even in this case there emerge severe restrictions on the fermion mixing pattern and the whole structure of the theory. In order not to be immediately excluded by the well-known bounds, the horizontal gauge fields {\it must} be the bulk modes, like gravitons. For the generic hierarchical breaking pattern the four-fermion operators induced by the tree-level exchange of the bulk gauge fields are unsuppressed for $N = 2$ . For $N > 3$ the suppression factor goes as a square of the largest $U (2)_{F}$ -non-invariant Yukawa coupling, which implies the lower bound $M_{P f} > 10$ TeV or so from the $K^{0} - K ˉ^{0}$ system. Situation is different in the scenarios when flavor Higgs fields live on a ( $3 + N^{'}$ )-brane of lower dimensionality than the gauge fields. The further suppression of gauge-mediated operators can be achieved by an explicit construction: for instance, if $U (2)_{F}$ is broken by a vacuum expectation value of the doublet, the troublesome operators are suppressed in the leading order, due to custodial SO(4) symmetry of the Higgs-gauge quartic coupling.

18 pages, Latex

Flavor Violation in Theories with TeV Scale Quantum Gravity

Abstract

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