No abstract

No abstract

The breaking of isospin symmetry in the electroweak theory with a dynamical Higgs sector is analyzed. The natural size of the breaking in various amplitudes is estimated, given that the breaking is very large in the fermion mass matrix. Special attention is paid to the parameter p = MwlMl cos 2 9 W . Hypercolor models are then investigated. There it is noted that p -1 will naturally exhibit a sensitive, linear dependence on the fermion-doublet mass splittings. PACS numbers: 12.10.Ck, ll.30.Jw The observation of the charged and neutral weak bosons 1,2 reinforces our belief in the standard model of color-electroweak interactions. The final missing link is an understanding of the mechanism of electroweak symmetry breaking. It is attractive to assume that the breaking arises spontaneously, and within this framework at least two distinct possibilities emerge. One is that of the light, elementary Higgs field whose weak self-interactions are arranged to give it a nonzero vacuum expectation value. A problem with this scheme is that truly elementary Higgs fields offer no understanding of fermion masses which are merely parametrized by the Yukawa couplings of the Higgs field to the fermions. Another possibility is that the spontaneous symmetry breakdown is due to new matter and strong forces at a mass scale around 1 TeV. In hypercolor models, for example, the Higgs sector is a set of bound states and resonances formed from new, strongly interacting fermions. 3 If new matter is involved, the masses of ordinary fermions must come from some direct interaction between the ordinary fermions and the new matter. In hypercolor models this must look like a four-fermion interaction or, at a deeper level, perhaps arise from the exchange of very massive (>10 TeV) extendedhypercolor bosons. While no realistic model of this sort has been constructed, it remains an attractive idea and one that at least offers the possibility of a deeper understanding of fermion masses.In either of these cases, the observed strong isospin nonconservation in the fermion mass matrix must be built into, if not explained by, the Lagrangian. It is important then to ask how this breaking infects other sectors of the theory through quantum corrections. In particular, one may expect correcy-yu(uldl) 0>" UR +yd(uLdi) -3>-