Isospin-Symmetry Breaking in Electroweak Theories

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 ρMW2MZ2cos2θW. Hypercolor models are then investigated. There it is noted that ρ1 will naturally exhibit a sensitive, linear dependence on the fermion-doublet mass splittings.