The 4-fold Pandharipande--Thomas vertex

We give a conjectural but full and explicit description of the (K-theoretic) equivariant vertex for Pandharipande–Thomas stable pairs on toric Calabi–Yau 4-folds, by identifying torus-fixed loci as certain quiver Grassmannians and prescribing a canonical half of the tangent-obstruction theory. For any number of non-trivial legs, the DT/PT vertex correspondence can then be verified by computer in low degrees.