The realizability criterion for complete intersection rings

Assume that a local ring RR has minimal regular presentation Q/IQ/I, let kk be its residue field, and fix minimal generators f1,,fnf_1,\ldots,f_n of II. Let

E=Q[e1,,enei=fi]E=Q[e_1,\ldots,e_n\mid \partial e_i=f_i]

and let

S=k[χ1,,χn],\mathcal{S}=k[\chi_1,\ldots,\chi_n],

where each χi\chi_i has cohomological degree 22. For an RR-complex MM with finitely generated homology, write VR(M){\rm V}_R(M) for its support variety in SpecS{\operatorname{Spec}^*}\mathcal{S}. Realizability conjecture. The ring RR is complete intersection if and only if 0\\{\bm{0}\\} is realizable as VR(M){\rm V}_R(M) for some RR-complex MM with H(M)\operatorname{H}(M) finitely generated. This proposes a converse to the known obstruction: over Cohen–Macaulay rings that are not complete intersections, every such complex with nonzero finitely generated homology has support variety of dimension at least 22, so the origin is not realizable. The complete-intersection direction follows from the established realizability of every closed subset, while the converse remains open in the stated generality.

Sources & referencesView supporting material

Primary source

Benjamin Briggs, Eloísa Grifo and Josh Pollitz, “The embedded deformation problem for monomial ideals”, arXiv:2506.10827 (2025).

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