Ideals of reduction number two

TL;DR

This paper investigates the Hilbert function of m-primary ideals with reduction number two in Cohen-Macaulay rings, establishing inequalities among Hilbert coefficients and exploring their relation to the depth of the associated graded ring.

Contribution

It proves a new inequality relating Hilbert coefficients for ideals with reduction number two and examines their connection to the depth of the associated graded ring.

Findings

Established the inequality e_1(I) ≥ e_0(I) - ℓ_A(A/I) + e_2(I) under certain conditions.

Connected Hilbert coefficients to the depth of the associated graded ring.

Extended previous work by Huneke, Ooishi, Sally, and Goto-Nishida-Ozeki.

Abstract

In a local Cohen-Macaulay ring $(A, \mathrm{m})$, we study the Hilbert function of an $\mathrm{m}$-primary ideal $I$ whose reduction number is two. It is a continuous work of the papers of Huneke, Ooishi, Sally, and Goto-Nishida-Ozeki. With some conditions, we show the inequality $\mathrm{e}_1(I)\ge \mathrm{e}_0(I) - \ell_A (A/I) + \mathrm{e}_2(I)$ of the Hilbert coefficients, which is the converse inequality of Sally and Itoh. We also study relations between the Hilbert coefficients and the depth of the associated graded ring.