(0,2) Landau-Ginzburg Models and Residues

We study the topological heterotic ring in (0,2) Landau-Ginzburg models without a (2,2) locus. The ring elements correspond to elements of the Koszul cohomology groups associated to a zero-dimensional ideal in a polynomial ring, and the computation of half-twisted genus zero correlators reduces to a map from the first non-trivial Koszul cohomology group to complex numbers. This map is a generalization of the local Grothendieck residue. The results may be applied to computations of Yukawa couplings in a heterotic compactification at a Landau-Ginzburg point.