Extended Gauge Sectors at Linear Colliders * †

Signatures of extended gauge models at high energy ee linear colliders are summarized. The phenomenology of models with extended gauge symmetries is particularly rich. The existence of new gauge bosons is one of the hallmarks of extended electroweak theories and their discovery would be a definitive signal for physics beyond the Standard Model (SM). However, extra gauge bosons are not the sole signature of an extended gauge group. These models also contain new exotic fermions, which are required for anomaly cancellation, as well as an enlarged Higgs sector, to facilitate the extended symmetry breaking. In addition, Supersymmetry may also be present, particularly in Grand Unified Theories (GUTS), to solve the hierarchy problem and to ensure the consistency of coupling constant unification with present data[1]. This talk will summarize the potential of high energy ee linear colliders to investigate the physics of new gauge bosons, at mass scales both above and equal to the machine center of mass energy, and to discover signals for exotic fermions. The subjects of extended Higgs sectors and Supersymmetry will be left to other speakers[2]. We begin with a brief review of several extended gauge models which presently appear in the literature. The most appealing set of enlarged electroweak models are those which are based on GUTS, examples being the unifying groups SO(10) and E6. In E6 string-inspired models[3] additional Z-bosons arise from the breaking chain E6 → SO(10)× U(1)ψ → SU(5)× U(1)χ × U(1)ψ → SM × U(1)θ , (1) where U(1)θ, which is a linear combination of U(1)χ and U(1)ψ, remains unbroken at low energies (< ∼ 10TeV). The fermion couplings of the extra Z-boson, Z , in this model take the form g 2cw √ 5xw/3(Qψ cos θ/ √ 6 − Qχ sin θ/ √ 10), where θ lies in the Research supported by the U.S. Department of Energy, Division of High Energy Physics, Contract W-31-109-ENG-38. Presented at the Workshop on Physics and Experiments with Linear ee Colliders, Waikoloa,