Flavor mixing in gauge-Higgs unification

Abstract

Gauge-Higgs unification is the fascinating scenario solving the hierarchy problem without supersymmetry. In this scenario, the Standard Model (SM) Higgs doublet is identified with extra component of the gauge field in higher dimensions and its mass becomes finite and stable under quantum corrections due to the higher dimensional gauge symmetry. On the other hand, Yukawa coupling is provided by the gauge coupling, which seems to mean that the flavor mixing and CP violation do not arise at it stands. In this talk, we discuss that the flavor mixing is originated from simultaneously non-diagonalizable bulk and brane mass matrices. Then, this mechanism is applied to various flavor changing neutral current (FCNC) processes via Kaluza-Klein (KK) gauge boson exchange at tree level and constraints for compactification scale are obtained.

B0−B¯0mixing in gauge-Higgs unification

“…It is highly non-trivial problem to explain the variety of fermion masses and flavor mixings in this scenario, since the gauge interactions should be universal for all matter fields, while the flavor symmetry has to be broken eventually in order to distinguish each flavor and to realize their mixings. In our previous papers [11,12], we addressed this issue and have clarified the mechanism to generate the flavor mixings by the interplay between bulk masses and the brane localized masses. 1 For the case of gravity-gauge-Higgs unification, see [4].…”

“…B This paper is organized as follows. After introducing our model in the next section, we summarize in section 3 how the flavor mixing is realized in the context of the gauge-Higgs unification, which was clarified and described in detail in our previous paper [11,12]. In section 4, as an application of the flavor mixing discussed in section 3, we calculate the mass difference of neutral B-mesons caused by the B We also obtain the lower bound for the compactification scale by comparing the obtained result with the experimental data.…”

“…In the previous papers, as typical processes of FCNC, we have calculated the K 0 -K 0 mixing and the D 0 -D 0 mixing amplitude at the tree level via non-zero KK gluon exchange and obtained the lower bounds for the compactification scale as the predictions of our model [11,12]. Interestingly, the obtained lower bounds of O(10) TeV were much milder than what we naively expect assuming that the amplitude is simply suppressed by the inverse powers of the compactification scale, say O(10 3 ) TeV.…”

“…Since our model reduces to the SM at low energies, there is no FCNC processes at the tree level with respect to the zero mode fields. However, it turns out that the exchange of non-zero Kaluza-Klein (KK) modes of gauge bosons causes FCNC at the tree level, though the rates of FCNC are suppressed by the inverse powers of the compactification scale ("decoupling") [11,12].…”

“…We may start with the base where the bulk mass terms are diagonalized, since the bulk mass terms are written in the form of hermitian matrix, which may be diagonalized by suitable unitary transformations, keeping the kinetic and gauge interaction terms of fermions invariant [11,12]. Even in this base, however, the brane-localized mass terms still have off-diagonal elements in the flavor base in general.…”