Top Quark Compositeness: Feasibility and Implications

TL;DR

This paper explores the feasibility of a mostly composite top quark within electroweak symmetry breaking models, analyzing constraints from electroweak precision tests and implications for LHC phenomenology.

Contribution

It provides a detailed analysis of the parameter space allowing high top compositeness and examines the impact on electroweak precision and collider signatures.

Findings

Light custodial partners weaken electroweak constraints.

Moderate positive T-parameter contributions can improve electroweak fit.

Enhanced high-energy four-top production at the LHC is predicted.

Abstract

In models of electroweak symmetry breaking in which the SM fermions get their masses by mixing with composite states, it is natural to expect the top quark to show properties of compositeness. We study the phenomenological viability of having a mostly composite top. The strongest constraints are shown to mainly come from one-loop contributions to the T-parameter. Nevertheless, the presence of light custodial partners weakens these bounds, allowing in certain cases for a high degree of top compositeness. We find regions in the parameter space in which the T-parameter receives moderate positive contributions, favoring the electroweak fit of this type of models. We also study the implications of having a composite top at the LHC, focusing on the process pp-> t\bar t t\bar t (b\bar b) whose cross-section is enhanced at high-energies.