Resolution and tor algebra structures of grade 3 ideals defining compressed rings

Abstract

Let R=k[x,y,z] be a standard graded 3-variable polynomial ring, where k denotes any field. We study grade 3 homogeneous ideals I⊆R defining compressed rings with socle k(−s)ℓ⊕k(−2s+1), where s⩾3 and ℓ⩾1 are integers. The case for ℓ=1 was previously studied in [8]; a generically minimal resolution was constructed for all such ideals. The paper [7] generalizes this resolution in the guise of (iterated) trimming complexes. In this paper, we show that all ideals of the above form are resolved by an iterated trimming complex. Moreover, we apply this machinery to construct ideals I such that R/I is a ring of Tor algebra class G(r) for some fixed r⩾2, and R/I may be chosen to have arbitrarily large type. In particular, this provides a new class of counterexamples to a conjecture of Avramov not already constructed by Christensen, Veliche, and Weyman in [5].