Massive Color-Octet Bosons: Bounds on Effects in Top-Quark Pair Production

TL;DR

This paper reviews constraints on massive color-octet bosons, highlighting their potential effects on top-quark pair production and establishing bounds on observable asymmetries in collider experiments.

Contribution

It provides a model-independent analysis of constraints on color-octet bosons and their impact on top-quark pair production, especially regarding forward-backward asymmetry.

Findings

Constraints from collider and electroweak data limit new physics effects.

Flavor non-universal couplings can avoid flavor-changing neutral currents.

An upper bound on top-quark asymmetry is derived for s-channel resonance exchange.

Abstract

A critical survey of the existing direct and indirect constraints on massive spin-one color octets is presented. Since such new degrees of freedom appear in any extension of the color gauge group to a product of at least two SU(3) factors, we keep our discussion as independent as possible from the underlying theory. In the framework of scenarios that involve flavor non-universal couplings, we show that excessive flavor-changing neutral currents can be avoided by a suitable alignment in flavor space. Constraints from electroweak precision observables and direct production at hadron colliders still leave space for sizable new-physics effects in top-quark pair production, in particular a large forward-backward asymmetry. In this context, we derive a model-independent upper bound on the asymmetry that applies whenever top-antitop production receives the dominant corrections from s-channel exchange of a new single color-octet resonance.