Schur powers of the cokernel of a graded morphism

Abstract

Let $\phi :F⟶G$ be a graded morphism between free R-modules of rank t and $t+c-1$, respectively, and let $I_j\left(\phi \right)$ be the ideal generated by the $j\times j$ minors of a matrix representing φ. In this paper: (1) We show that the canonical module of $R/I_j\left(\phi \right)$ is up to twist equal to a suitable Schur power ${\Sigma }^{I}M$ of $M=\mathrm{coker}\left({\phi }^{⁎}\right)$; thus equal to ${\wedge }^{t+1-j}M$ if $c=2$ in which case we find a minimal free R-resolution of ${\wedge }^{t+1-j}M$ for any j, (2) For $c=3$, we construct a free R-resolution of ${\wedge }^{2}M$ which starts almost minimally (i.e. the first three terms are minimal up to a precise summand), and (3) For $c\ge 4$, we construct under a certain depth condition the first three terms of a free R-resolution of ${\wedge }^{2}M$ which are minimal up to a precise summand. As a byproduct we answer the first open case of a question posed by Buchsbaum and Eisenbud in [2, pg. 299].