Effects of Top Compositeness

TL;DR

The paper tackles whether top-quark compositeness can coexist with precision electroweak constraints while yielding observable effects at colliders. It adopts an effective field theory below the compositeness scale $\Lambda$, parameterized by a second scale $f$ and dimension-six operators with coefficients estimated via naive dimensional analysis, examining how $S$, $T$, $U$ oblique parameters and $\Gamma(Z\rightarrow b\bar b)$ constrain the new physics. Two scenarios are analyzed: right-handed-only compositeness and left-handed top-doublet compositeness, with mixing angles $\theta^u_L$, $\theta^c_L$, $\theta^u_R$, $\theta^c_R$ bounded by flavor physics. The findings show strong constraints pushing $\Lambda_{L}$ to higher scales for left-handed compositeness, while right-handed compositeness allows a lower $\Lambda$ and potentially sizable effects, including possible enhancements in $t\bar t$ production, highlighting distinctive experimental signatures of the two scenarios.

Abstract

We investigate the effects of top quark compositeness on various physical parameters, and obtain lower limits on the compositeness scale from electroweak precision data. We consider corrections to top quark decay rates and other physical processes. Our results depend sensitively on whether the left-handed top is composite. A considerable enhancement of $t \bar t$ production is possible if only the right-handed top is composite.