Impact of dimension-eight SMEFT contributions: A case study

The use of the Standard Model effective field theory 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-six operators. The numerical impact of the next terms in the series, the dimension-eight operators, is unknown in general. We consider a specific BSM model containing a charge-2/3 heavy vectorlike quark and compute the operators generated at dimension eight. The numerical effects of these operators are studied for the t $(t) over bar $h process, where they contribute at tree level and we find effects at the O(0.5-2%) level for allowed values of the parameters.

Automated summary

The use of the Standard Model effective field theory Lagrangian is common in studying Beyond the Standard Model effects in collider experiments. This study focuses on a specific BSM model with a charge-2/3 heavy vectorlike quark and computes the operators generated at dimension eight. Numerical effects of these operators on the $t\bar{t}h$ process are found to be around 0.5-2% for allowed parameter values.