Symmetry breaking and effecto of heavy particles in electro-weak gauge theories

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The gauge theory based on the group SU(3) X SU(2)_L X U(1) is in good accord (with some uncertainty) with various kinds of measurements in electro-weak interactions. For this model to be established as the unified theory of strong and electro-weak interactions, it is crucial to make precision testy of radiative corrections in this theory. The purposes of the present research project are the following :a) To study the physics law at energies E higher than the weak-boson mass scale M_W, in particular, the effects of possible heavy particles through radiative corrections in light particle processes.b) Research aiming at understanding the nature of the Higgs particle.c) Phenomenological study to determine the properties of quarks and leptons.Regarding the purposes a) and c) we have studied the non-decoupling effects of heavy particles in the gauge boson two- and three-point couplings and have obtained a few interesting results (as summarized in the report "Precision Test of Electro-Weak Parameters and New Physics" ) :1) The analysis of the symmetry properties of the S, T, U parameters of the two-point functions is useful in understanding the oblique corrections.2) Comparison with the precision measurements of S and T gives a meaningful upper bound on the number of extra generations N_<eg>.3) Regarding the triple gauge-boson couplings, we have identified the four parameters which are sufficient to describe the non-decoupling effects of heavy particles in the gammaW^+W^- and Z^OW^+W_- couplings.As for the purpose b), we have studied the properties of the Higgs in theories in which it is given a geometrical role in extra dimensions of space-time. The research in this direction is still in progress.