Technifermion representations and precision electroweak constraints

We discuss the selection of fermion representations in technicolor models with a view toward minimizing technicolor contributions to the precision electroweak S parameter. We present and analyze models that involve one technifermion SU(2)(L) doublet with standard-model singlet technifermion sectors that lead to walking behavior, which further reduces S. We also consider models that have technifermions in higher-dimensional representations and study embeddings in extended technicolor theories. (c) 2005 Elsevier B.V. All rights reserved.