Z' Gauge Models from Strings

Potentially realistic string models often contain additional abelian gauge factors besides the standard model group. The consequences of such extended gauge structure are manifold both for theory and phenomenology as I show focussing in the simplest case of just one additional non-anomalous U(1)‘. First, I discuss the possible symmetry breaking patterns according to the scale at which the U(1)’ symmetry gets broken: in the first case, that scale must be below ~ 1 TeV to avoid fine-tuning; in the second case, the breaking can take place along a flat direction at an intermediate scale between the string scale and the electroweak scale. In both cases, I present a number of the generic implications expected, e.g. for the mu problem, Z’ and Higgs physics, dark matter and fermion masses.