Supersymmetry and electroweak breaking with large and small extra dimensions

We consider the problem of supersymmetry and electroweak breaking in a 5d theory compactified on an S-1/Z(2) orbifold, where the extra dimension may be large or small. We consider the case of a supersymmetry breaking 4d brane located at one of the orbifold fixed points with the Standard Model gauge sector, third family and Higgs fields in the 5d bulk, and the first two families on a parallel 4d matter brane located at the other fixed point. We compute the Kaluza-Klein mass spectrum in this theory using a matrix technique which allows us to interpolate between large and small extra dimensions. We also consider the problem of electroweak symmetry breaking in this theory and localize the Yukawa couplings on the 4d matter brane spatially separated from the brane where supersymmetry is broken. We calculate the 1-loop effective potential using a zeta-function regularization technique, and find that the dominant top and stop contributions are separately finite. Using this result we find consistent electroweak symmetry breaking for a compactification scale 1/R approximate to 830 GeV and a lightest Higgs boson mass m(h) approximate to 170 GeV. (C) 2001 Elsevier Science B.V. All rights reserved.