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In this paper we propose a possible explanation to the Fermion mass hierarchyproblem by fitting the type-II seesaw mechanism into the Higgs doublet sector,such that their vacuum expectation values are hierarchal. We extend theStandard Model with two extra Higgs doublets as well as a spontaneously broken$U_X(1)$ gauge symmetry. All the fermion Yukawa couplings except that of topquark are of order ${\cal O} (10^{-2})$ in our model. Constraints on theparameter space from Electroweak precision measurements are studied. Besides,the neutral component of the new fields, which are introduced to cancel theanomalies of the $U(1)_X$ gauge symmetry can be dark matter candidate. Weinvestigate its signature in the dark matter direct detection.

A Three Higgs Doublet Model for the Fermion Mass Hierarchy Problem