The physics of heavy Z^′ gauge bosons

The U(1)^′ symmetry associated with a possible heavy Z^′ would have profound implications for particle physics and cosmology. The motivations for such particles in various extensions of the standard model, possible ranges for their masses and couplings, and classes of anomaly-free models are discussed. Present limits from electroweak and collider experiments are briefly surveyed, as are prospects for discovery and diagnostic study at future colliders. Implications of a Z^′ are discussed, including an extended Higgs sector, extended neutralino sector, and solution to the μ problem in supersymmetry; exotic fermions needed for anomaly cancellation; possible flavor changing neutral current effects; neutrino mass; possible Z^′ mediation of supersymmetry breaking; and cosmological implications for cold dark matter and electroweak baryogenesis.