The Impact of Dimension-8 SMEFT Contributions: A Case Study

TL;DR

This paper investigates the numerical impact of dimension-8 SMEFT operators generated by a specific BSM model on the $tar{t}h$ process, revealing effects at the sub-percent to two percent level, which are typically neglected.

Contribution

It provides a detailed case study of dimension-8 SMEFT contributions from a specific BSM model, quantifying their effects on collider observables.

Findings

Dimension-8 operators contribute at 0.5-2% level in $tar{t}h$ production.

The study highlights the importance of considering higher-dimensional operators in SMEFT analyses.

Numerical effects depend on the parameters of the BSM model.

Abstract

The use of the SMEFT Lagrangian to quantify possible Beyond the Standard Model (BSM) effects is standard in LHC and future collider studies. One of the usual assumptions is to truncate the expansion with the dimension-$6$ operators. The numerical impact of the next terms in the series, the dimension-$8$ operators, is unknown in general. We consider a specific BSM model containing a charge-${2 3}$ heavy vector-like quark and compute the operators generated at dimension-$8$. The numerical effects of these operators are studied for the $t\bar{t}h$ process, where they contribute at tree level and we find effects at the ${\cal{O}}(0.5-2\%)$ level for allowed values of the parameters.