Unscrambling new models for higher-energy physics

Abstract

Abstract. There is strong evidence that new physical degrees of freedom and new phenomena exist and may be revealed in future collider experiments. The best hints of what this new physics might be are provided by electroweak symmetry breaking. I briefly review certain theories for physics beyond the standard model, including the top-quark seesaw model and universal extra dimensions. A common feature of these models is the presence of vector-like quarks at the TeV scale. Then I discuss the role of a linear e + e − collider in disentangling this new physics. THE CASE FOR NEW PHYSICSThe observed fundamental particles, namely the SU(3) C × SU(2) W × U(1) Y gauge bosons, the longitudinal degrees of freedom of the W ± and Z 0 , and three generations of quarks and leptons, may explain in principle all observed physical phenomena. However, there is strong evidence for the existence of new phenomena at higher energy scales than the ones probed so far. The most robust argument is provided by the perturbative violation of unitarity in the W W scattering, at a scale of order 1 TeV [1]. Therefore, either the W and Z have strongly coupled selfinteractions at the TeV scale, or new fundamental degrees of freedom exist. The scale of these new phenomena is within the reach of future collider experiments, and exploring them is at the heart of high-energy physics.The standard model accomodates rather well all available data, especially when the Higgs boson is light [2]. More generally, any model with a decoupling limit [3] given by the standard model is viable, at least in that limit. These are models in 1) Plenary talk at the 5th International Linear Collider Workshop (LCWS 2000), Fermilab, October 24-28, 2000