Fermion Mass Hierarchy in Grand Gauge-Higgs Unification

Grand gauge-Higgs unification of five dimensional $SU(6)$ gauge theory on an orbifold $S^1/Z_2$ is discussed. The Standard model (SM) fermions are introduced on one of the boundaries and some massive bulk fields are also introduced so that they couple to the SM fermions through the mass terms on the boundary. Integrating out the bulk fields generates the SM fermion masses with exponentially small bulk mass dependences. The SM fermion masses except for top quark are shown to be reproduced by mild tuning the bulk masses. One-loop Higgs potential is calculated and it is shown that the electroweak symmetry breaking occurs by introducing additional bulk fields. Higgs boson mass is also computed.