Conjecture on unbounded ranks of small maximal Cohen–Macaulay modules

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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.

References

Primary source

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

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