Technifermion Representations and Precision Electroweak Constraints

TL;DR

The paper addresses how technicolor models can satisfy precision electroweak constraints by selecting technifermion representations to minimize the S parameter. It proposes a minimal SU(2)_{TC} model with an SM-nonsinglet doublet in the fundamental and a walking SM-singlet sector mediated by metacolor, achieving walking while keeping S small. It also analyzes the viability of higher-dimensional technifermion representations and their embedding into ETC, showing that many such constructions either increase S or lose asymptotic freedom. The work highlights the prospects and challenges of building ETC-compatible, walking technicolor theories that remain consistent with current electroweak data.

Abstract

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.