The top quark right coupling in the tbW-vertex

TL;DR

This paper calculates the standard model contributions to the top quark's right-handed coupling in the $tbW$ vertex and proposes LHC observables to measure it, aiding the search for new physics.

Contribution

It provides the first detailed calculation of electroweak and QCD effects on the $V_R$ coupling and introduces observables that isolate this coupling at the LHC.

Findings

Standard model predicts a small but non-zero $V_R$ due to loop effects.

Proposed observables are sensitive to $V_R$ and free from tree-level standard model contributions.

Results enable setting bounds on new physics models affecting the $tbW$ vertex.

Abstract

The most general parametrization of the $tbW$ vertex includes a right coupling $V_R$ that is zero at tree level in the standard model. This quantity may be measured at the Large Hadron Collider where the physics of the top decay is currently investigated. This coupling is present in new physics models at tree level and/or through radiative corrections, so its measurement can be sensitive to non standard physics. In this paper we compute the leading electroweak and QCD contributions to the top $V_R$ coupling in the standard model. This value is the starting point in order to separate the standard model effects and, then, search for new physics. We also propose observables that can be addressed at the LHC in order to measure this coupling. These observables are defined in such a way that they do not receive tree level contributions from the standard model and are directly proportional to the right coupling. Bounds on new physics models can be obtained through the measurements of these observables.