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 Mpf ∼ 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 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 Mpf> 10 TeV or so from the K0 - K̄0 system. Situation is different in the scenarios when flavor Higgs fields (and thus familons) 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.
|Original language||English (US)|
|Number of pages||10|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - 1999|
ASJC Scopus subject areas
- Nuclear and High Energy Physics