Supersymmetry and finite radiative electroweak breaking from an extra dimension

A five-dimensional N = 1 supersymmetric theory compactified on the orbifold S-1/Z (2) is constructed. Gauge fields and SU(2)(L) singlets propagate in the bulk (U-states) while SU(2)(L) doublets are localized at an orbifold fixed point brane (T-states). Zero bulk modes and localized states constitute the MSSM and massive modes are arranged into N = 2 supermultiplets. Superpotential interactions on the brane are of the type UTT. Supersymmetry is broken in the bulk by a Scherk-Schwarz mechanism using the U(1)(R) global R-symmetry. A radiative finite electroweak breaking is triggered by the top-quark/squark multiplet T propagating in the bulk. The compactification radius R is fixed by the minimization conditions and constrained to be 1/R less than or similar to 10-15 TeV. It is also constrained by precision electroweak measurements to be 1/R greater than or similar to 4 TeV. The pattern of supersymmetric mass spectrum is well defined. In particular, the lightest supersymmetric particle is the sneutrino and the next to lightest supersymmetric particle the charged slepton, with a squared-mass difference similar to M-Z(2) The theory couplings, gauge and Yukawa, remain perturbative up to scales E given, at one-loop, by ER less than or similar to 30-40. Finally, LEP searches on the MSSM Higgs sector imply an absolute lower bound on the SM-like Higgs mass, around 145 GeV in the one-loop approximation. (C) 2001 Elsevier Science B.V. All rights reserved.