1995/11/28 by Mirjam Cvetic, Paul Langacker · 2 citations
Physics and Astronomy · #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevd.54.3570
published as Phys.Rev.D54:3570-3579,1996 · 20 Pages, uses RevTeX (additional references and comments added)
arxiv created 1995/11/28 · arxiv updated 2009/11/30
Within a class of superstring vacua which have an additional non-anomalous U(1)' gauge factor, we address the scale of the U(1)' symmetry breaking and constraints on the exotic particle content and their masses. We also show that an extra gauge U(1)' provides a new mechanism for generating a naturally small effective μ term. In general, existing models are not consistent with all phenomenological constraints; however, they do provide a testing ground to address the above issues, yielding a set of concrete scenarios. Under the assumptions that the spontaneous U(1)' breaking takes place in the observable sector and that the supersymmetry breaking scalar mass square terms are positive at the string scale, the breaking of U(1)' symmetry is radiative. It can take place when the appropriate Yukawa couplings of exotic particles are of order one, which occurs for Z2× Z2 fermionic orbifold constructions at symmetric points of moduli space. The Z' mass is either of \cal O(MZ), when the symmetry breaking is due to a single standard model singlet, or is of a scale intermediate between the string and electro-weak scales, determined by the radiative corrections (or by competing non-renormalizable operators), when the breaking is due to two or more mirror-like singlets. In the former case, the MZ'/MZ hierarchy achievable without excessive fine tuning is within future experimental reach.