# Off-shell single-top-quark production in the Standard Model Effective Field Theory

## TL;DR

This paper provides a detailed NLO QCD calculation of off-shell single-top-quark production within the Standard Model and SMEFT, including all relevant operators and effects, and makes the framework publicly accessible.

## Contribution

It introduces a fully differential, spin-dependent NLO QCD calculation for off-shell single-top production in SMEFT, including higher order operators and off-shell effects, with publicly available code.

## Key findings

- Inclusion of all relevant SMEFT operators at 1/Λ^2 at NLO
- Consideration of chirality-flipping operators at 1/Λ^4
- Framework available in the MCFM software

## Abstract

We present a fully differential and spin-dependent $t$-channel single-top-quark calculation at next-to-leading order (NLO) in QCD including off-shell effects by using the complex mass scheme in the Standard Model (SM) and in the Standard Model Effective Field Theory (SMEFT). We include all relevant SMEFT operators at $1/\Lambda^2$ that contribute at NLO in QCD for a fully consistent comparison to the SM at NLO. In addition, we include chirality flipping operators that do not interfere with the SM amplitude and contribute only at $1/\Lambda^4$ with a massless $b$-quark. Such higher order effects are usually captured by considering anomalous right-handed $Wtb$ and left-handed $Wtb$ tensor couplings. Despite their formal suppression in the SMEFT, they describe an important class of models for new physics. Our calculation and analysis framework is publicly available in MCFM.