| Themes > Science > Physics > Elementary particle physics > Elementary particle physics Today > Elementary particle physics Today > Beyond the Standard Model |
Many of the elements of the simple Higgs mechanism for electroweak symmetry breakdown can be retained if an additional symmetry between bosons and fermions, called supersymmetry, were to exist. This elegant symmetry alleviates quantum instabilities in the theory, at the expense of introducing a host of new elementary particles at masses near 1 TeV. In supersymmetric theories, essentially every particle in Table A has a supersymmetric boson or fermion partner. Currently, supersymmetry has no direct experimental support; however, supersymmetric grand unified theories correctly predict low-energy coupling strengths. Additional strong motivation for supersymmetry is provided by superstring theories, which unify the Standard Model and gravity by replacing point particles with tiny strings. Many supersymmetric theories, furthermore, predict the existence of heavy, stable, neutral particles that have the potential to explain the missing mass of the universe. Astronomical observations indicate that visible objects might comprise less than 10% of the total mass of the universe. With its plethora of new particles, supersymmetric theories can solve this problem. If true, this would have profound implications for our place in the universe: we would not be made of the material that comprises the bulk of the universe! Alternative to an elementary Higgs particle is dynamical symmetry breaking via fermion-antifermion interactions. This is analogous to the Bardeen-Cooper-Schrieffer theory of superconductivity in which electron- electron Cooper pairs replace the scalar order parameter of the Landau- Ginsberg phenomenological theory. Scenarios for electroweak symmetry breaking along these lines range from minimal top-antitop interactions to more ambitious schemes modeled on QCD. These models often predict many new heavy particles below the TeV scale. Although the basic premise of these speculations is very appealing, no complete dynamical theory currently exists. We do, however, expect that new particles or interactions should appear, at a mass scale below a few TeV. To make headway in unfolding dynamical symmetry breaking will require accelerators of the highest possible energy to discover new heavy fermions and bosons or some complete surprise. Such discoveries would provide the clues necessary to help guide our imaginations about the underlying dynamics. In addition to supersymmetry and dynamical symmetry breaking, there have been many other possible suggestions for new physics. They include: extended symmetries with additional heavy gauge bosons W', Z', neutrino masses and associated oscillations among the three different species, new sources of CP violation, grand unification of strong and electroweak interactions, etc. The menu of possibilities is rich. Full exploration will require a diverse and broad-based experimental program that utilizes accelerator and non-accelerator facilities. Theorists may speculate, but data rules supreme in the study of nature. |
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