Effective-Field-Theory Approach to Top-Quark Production and Decay

TL;DR

This paper develops a model‑independent effective field theory framework for top quark interactions using dimension‑six operators invariant under the SM gauge group. It shows that the leading deviations from the Standard Model arise from interference terms of order $1/\Lambda^2$ and identifies a focused set of 15 operators that impact top decay, single‑top production, and top pair production. By deriving how these operators modify decay rates, angular and energy distributions, cross sections, and spin observables (including CP‑odd asymmetries), the work provides a comprehensive, testable map from new physics at scale $\Lambda$ to measurable collider signatures. The results enable systematic bounds on possible beyond‑SM physics and highlight polarized‑top observables as essential probes of CP violation in the top sector, with practical strategies across the three production/decay modes and dedicated CP‑odd measurements in the CP‑odd operator sector.

Abstract

We discuss new physics in top-quark interactions, using an effective field theory approach. We consider top-quark decay, single top production, and top-quark pair production. We identify 15 dimension-six operators that contribute to these processes, and we compute the deviation from the Standard Model induced by these operators. The results provide a systematic way of searching for (or obtaining bounds on) physics beyond the Standard Model.

Figures (12)

• Figure 1: The Feynman diagrams for $t\rightarrow be^+\nu$. (a) is the SM amplitude; (b) represents the vertex correction induced by the operator $O_{\phi q}^{(3)}$ and $O_{tW}$.
• Figure 2: The differential decay rate induced by different operators. The curves are normalized so that the area is the same.
• Figure 3: The energy dependence of the electron.
• Figure 4: The energy dependence of the neutrino.
• Figure 5: Feynman diagrams for the $s$- and $t$-channel single top production. (a-c) are the $s$-channel diagrams, while (d-f) are the $t$-channel diagrams. (a,d) are the SM amplitude, (b,e) are the correction from $O_{\phi q}^{(3)}$ and $O_{tW}$, and (c,f) are the four-fermion interaction from $O_{qq}^{(1,3)}$. The diagrams for the $t$-channel process $\bar{d}b\rightarrow \bar{u}t$ can be obtained by interchanging $u$ and $d$ quarks in (d-f).