Ratliff-Rush filtration, Hilbert coefficients and the reduction number of integrally closed ideals (2304.04524v1)

Abstract: Let $(R,\mathfrak{m})$ be a Cohen-Macaulay local ring of dimension $d\geq 3$ and $I$ an integrally closed $\mathfrak{m}$-primary ideal. We establish bounds for the third Hilbert coefficient $e_3(I)$ in terms of the lower Hilbert coefficients $e_i(I),~0\leq i\leq 2$ and the reduction number of $I$. When $d=3$, the boundary cases of these bounds characterize certain properties of the Ratliff-Rush filtration of $I$. These properties, though weaker than depth $G(I)\geq 1$, guarantees that Rossi's bound for reduction number $r_J(I)$ holds in dimension three. In that context, we prove that if $depth G(I)\geq d-3$, then $r_J(I)\leq e_1(I)-e_0(I)+\ell(R/I)+1+e_2(I)(e_2(I)-e_1(I)+e_0(I)-\ell(R/I))-e_3(I).$ We also discuss the signature of the fourth Hilbert coefficient $e_4(I).$