Measuring the W-t-b interaction at the ILC

The large top quark mass suggests that the top plays a pivotal role in electroweak symmetry-breaking dynamics and, as a result, may have modified couplings to electroweak bosons. Hadron colliders can provide measurements of these couplings at the similar to 10% level, and one of the early expected triumphs of the International Linear Collider (ILC) is to reduce these uncertainties to the percent level. In this article, we propose the first direct measurement of the standard model W-t-b coupling at the ILC, from measurements of tt-like signals below the tt production threshold. We estimate that the ILC with 100 fb(-1) can measure a combination of the coupling and top width to high precision, and when combined with a direct measurement of the top width from the above-threshold scan, results in a model-independent measurement of the W-t-b interaction of the order of similar to 3%.