arXiv subjects

Maria Evelina Rossi

Publications and source records attributed to Maria Evelina Rossi.

26 records · Page 2Linked to original sources

arXiv2009

Integrally closed and componentwise linear ideals

In two dimensional regular local rings integrally closed ideals have a unique factorization property and have a Cohen-Macaulay associated graded ring. In higher dimension these properties do not hold for general integrally closed ideals and the goal of the paper is to identify a subclass of integrally closed ideals for which they do. We restrict our attention to 0-dimensional homogeneous ideals in polynomial rings $R$ of arbitrary dimension and identify a class of integrally closed ideals, the Goto-class $\G^*$, that is closed under product and that has a suitable unique factorization property. Ideals in $\G^*$ have a Cohen-Macaulay associated graded ring if either they are monomial or $\dim R\leq 3$. Our approach is based on the study of the relationship between the notions of integrally closed, contracted, full and componentwise linear ideals.

math.AC↗

arXiv2009

Consecutive cancellations in Betti numbers of local rings

Let I be a homogeneous ideal in a polynomial ring P over a field. By Macaulay's Theorem, there exists a lexicographic ideal L=Lex(I) with the same Hilbert function as I. Peeva has proved that the Betti numbers of P/I can be obtained from the graded Betti numbers of P/L by a suitable sequence of consecutive cancellations. We extend this result to any ideal I in a regular local ring (R,m) by passing through the associated graded ring. To this purpose it will be necessary to enlarge the list of the allowed cancellations. Taking advantage of Eliahou-Kervaire's construction, several applications are presented. This connection between the graded perspective and the local one is a new viewpoint and we hope it will be useful for studying the numerical invariants of classes of local rings.

math.AC↗

arXiv2007

Contracted ideals and the Groebner fan of the rational normal curve

The paper has two goals: the study the associated graded ring of contracted homogeneous ideals in $K[x,y]$ and the study of the Groebner fan of the ideal $P$ of the rational normal curve in ${\bf P}^d$. These two problems are, quite surprisingly, very tightly related. We completely classify the contracted ideals with a Cohen-Macaulay associated graded rings in terms of the numerical invariants arising from Zariski's factorization. We determine explicitly all the initial ideals (monomial or not) of $P$ that are Cohen-Macaulay.

math.AC↗

arXiv2004

Castelnuovo-Mumford Regularity and finiteness of Hilbert Functions

The notion of regularity has been used by S. Kleiman in the construction of bounded families of ideals or sheaves with given Hilbert polynomial, a crucial point in the construction of Hilbert or Picard scheme. In a related direction, Kleiman proved that if I is an equidimensional reduced ideal in a polynomial ring S over an algebraically closed field, then the coefficients of the Hilbert polynomial of R = S/I can be bounded by the dimension and the multiplicity of R. Srinivas and Trivedi proved that the corresponding result does not hold for a local domain. However, they proved that there exist a finite number of Hilbert functions for a local Cohen-Macaulay ring of given multiplicity and dimension. The proofs of the above results are very difficult and involve deep results from Algebraic Geometry. The aim of this paper is to introduce a unified approach which gives more general results and easier proofs of the above mentioned results. This approach is based on the fact that a class C of standard graded algebras has a finite number of Hilbert functions if and only if there are upper bounds for the regularity and the embedding dimension of the members of C.

math.AC↗

arXiv2004

Graded rings associated with contracted ideals

By definition, an $\m$-primary ideal $I$ in a 2-dimensional regular local ring $(R, \m)$ is contracted if $I=R \cap IR[\m/x]$ for some $x \in \m \setminus \m^2$. Contracted ideals have been introduced by Zariski and used for proving the unique factorization theorem for complete (i.e. integrally closed) ideals. Any complete ideal is contracted but not the other way round. While the associated graded rings to complete ideals are always Cohen-Macaulay, this is not the case for contracted ideals. Our goal is to study depth, Hilbert function and defining equations of the graded rings of homogeneous contracted ideals. We show, by using quadratic transform, that the depth of the associated graded ring to a contracted ideal $I$ is determined by depth of the associated graded rings to a certain family of monomial ideals (indeed lex-segments) which are naturally attached to $I$. For certain classes of contracted ideals we show that the associated graded ring is Cohen-Macaulay or at least has positive depth.

math.AC↗

arXiv2003

Depth of associated graded rings via Hilbert coefficients of ideals

Given a local Cohen-Macaulay ring $(R, {\mathfrak m})$, we study the interplay between the integral closedness -- or even the normality -- of an ${\mathfrak m}$-primary $R$-ideal $I$ and conditions on the Hilbert coefficients of $I$. We relate these properties to the depth of the associated graded ring of $I$.

math.AC↗

arXiv2002

Castelnuovo-Mumford regularity and extended degree

The main result of this paper shows that the Castelnuovo-Mumford regularity of the tangent cone of a local ring is effectively bounded by the dimension and any extended degree. From this it follows that there are only a finite number of Hilbert-Samuel functions of local rings with given dimension and extended degree.

math.AC↗

arXiv2002

Notes on the behavior of the Ratliff-Rush filtration

We establish new classes of Ratliff-Rush closed ideals and some pathological behavior of the Ratliff-Rush closure. In particular, Ratliff-Rush closure does not behave well under passage modulo superficial elements, taking powers of ideals, associated primes, leading term ideals, and the minimal number of generators. In contrast, the reduction number of the Ratliff-Rush filtration behaves better: it preserves some information on the reduction number of the ideal.

math.AC↗