The Dao-number regularity conjecture for ideals

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Let (R,m)(R,\mathfrak{m}) be the local ring under consideration, let I⊂RI\subset R be an ideal, let R(m)=⨁k≥0mk\mathcal{R}(\mathfrak{m})=\bigoplus_{k\ge0}\mathfrak{m}^k be the Rees algebra of m\mathfrak{m}, and let R(m,I)=⨁k≥0Imk\mathcal{R}(\mathfrak{m},I)=\bigoplus_{k\ge0}I\mathfrak{m}^k be the extension of II in R(m)\mathcal{R}(\mathfrak{m}). Write d1(I)\mathfrak{d}_1(I), d2(I)\mathfrak{d}_2(I), and d3(I)\mathfrak{d}_3(I) for the Dao numbers of II. Dao-number regularity conjecture. For all ideals I⊂RI\subset R:

d2(I)≤d3(I)=d1(I)≤reg⁡R(m)R(m,I).\mathfrak{d}_2(I)\le\mathfrak{d}_3(I)=\mathfrak{d}_1(I)\le\operatorname{reg}_{\mathcal{R}(\mathfrak{m})}\mathcal{R}(\mathfrak{m},I).

The paper proves this bound under additional hypotheses, namely when depth⁡gr⁡m(I)>0\operatorname{depth}\operatorname{gr}_{\mathfrak{m}}(I)>0 or when RR is regular; the conjecture asserts that the same inequality holds for every ideal in the setting considered.

References

Primary source

Antonino Ficarra, “Dao numbers and the asymptotic behaviour of fullness”, arXiv:2402.05555 (2025).

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