Conjecture on unbounded ranks of small maximal Cohen–Macaulay modules

A small maximal Cohen–Macaulay module over a local ring is a finitely generated maximal Cohen–Macaulay module whose multiplicity satisfies the smallness bound discussed in the source. For a positive integer NN, saying that a ring admits no small maximal Cohen–Macaulay module of rank at most NN means that every such module has rank greater than NN.

Unbounded-rank small maximal Cohen–Macaulay conjecture. For every integer NN, there exists a complete local domain RR that does not admit small maximal Cohen–Macaulay modules of rank N\leq N.

This conjecture is motivated by examples where small maximal Cohen–Macaulay modules exist only in higher rank, while the preceding result rules out rank-one maximal Cohen–Macaulay modules in a family of complete local domains. The source gives no resolution.

Sources & referencesView supporting material

Primary source

Linquan Ma, “Maximal Cohen-Macaulay modules over certain Segre products”, arXiv:1802.04786 (2018).

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