Electroweak symmetry breaking and large extra dimensions

In supersymmetric theories with large extra dimensions a finite radiative electroweak symmetry breaking can be triggered if the top/stop multiplet propagates in the bulk of the extra dimensions. We have constructed a consistent supersymmetric five-dimensional model where the extra coordinate is compactified on the orbifold S¹/₂, with radius R, and exhibiting as generic features: large tan β≃m_t/m_b, a well defined pattern of Higgs and supersymmetric mass spectra, sneutrinos as the LSP and perturbative couplings for scales as large as ~ 40/R. In order to understand the finiteness of the Higgs mass, which requires the contribution of KK-modes heavier than the cut-off of the five-dimensional theory (Λ~M_s, the string scale), we have introduced a string-motivated regularization where those heavy KK-modes decouple exponentially as exp {-M²_KK/2Λ²}. The regularization does not spoil the five-dimensional structure and the finite result is recovered in the limit Λ→∞. We stress that a top in the bulk should lead to observable phenomenological and experimental consequences.