S. El Baghdadi, L. Izelgue, S. Kabbaj
This paper studies the class group of graded integral domains. As an application, we state a decomposition theorem for class groups of semigroup rings. This recovers well-known results developed for the classic contexts of polynomial rings and Krull semigroup rings. Our results are backed by original examples.
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On graded Going down domains
本文针对无挠交换可消幺半群上的分次整环，引入分次下降整环概念，给出分次Prüfer整环的等价刻画，借助分次可除整环刻画该类整环，并证明其下降性质在商整环下稳定。
On graded going-down domains, II
本文研究了回拉中分级整环的分级下行性质，并据此构造了该类整环的原创性实例。
Let $R=\bigoplus_{α\inΓ}R_α$ be a graded integral domain graded by an arbitrary grading torsionless monoid $Γ$, and $\star$ be a semistar operation on $R$. In this paper we define and study the graded integral domain analogue of $\star$-Nagata and Kronecker function rings of $R$ with respect to $\star$. We say that $R$ is a graded Prüfer $\star$-multiplication domain if each nonzero finitely generated homogeneous ideal of $R$ is $\star_f$-invertible. Using $\star$-Nagata and Kronecker function rings, we give several different equivalent conditions for $R$ to be a graded Prüfer $\star$-multipli…
The literature in persistent homology often refers to a "structure theorem for finitely generated graded modules over a graded principal ideal domain". We clarify the nature of this structure theorem in this context.
Graded Perinormality
本文引入分次近正规与分次全局近正规整环概念，证明经典近正规性结果的分次类比，并研究分次整环与其第0个分次分量间的性质下降关系。
Let P be a lattice polytope with $h^*$-vector $(1, h^*_1, h^*_2)$. In this note we show that if $h_2^* \leq h_1^*$, then $P$ is IDP. More generally, we show the corresponding statements for semi-standard graded Cohen-Macaulay domains over algebraically closed fields.
Let $R=\bigoplus_{α\inΓ}R_α$ be a graded integral domain and $\star$ be a semistar operation on $R$. For $a\in R$, denote by $C(a)$ the ideal of $R$ generated by homogeneous components of $a$ and for$f=f_0+f_1X+\cdots+f_nX^n\in R[X]$, let $\A_f:=\sum_{i=0}^nC(f_i)$. Let $N(\star):=\{f\in R[X]\mid f\neq0\text{and}\A_f^{\star}=R^{\star}\}$. In this paper we study relationships between ideal theoretic properties of $\NA(R,\star):=R[X]_{N(\star)}$ and the homogeneous ideal theoretic properties of $R$. For example we show that $R$ is a graded Prüfer-$\star$-multiplication domain if and only if $\NA…
Graded Injective Domains
本文研究分次 $i$-整环与分次配对整环，并揭示其与 gr-Prüfer 整环之间的关联。
For a graded domain $R=k[X_0,...,X_m]/J$ over an arbitrary domain $k$, it is shown that the ideal generated by elements of degree $\geq mA$, where $A$ is the least common multiple of the weights of the $X_i$, is a normal ideal.
Restrictions on Hilbert coefficients give depths of graded domains
该研究通过分次多项式环中齐次素理想添加一般线性形式后希尔伯特系数的变化特征，给出了商环深度的判定准则，并关联了素理想通用初始理想的约束条件。
For a Mori dream space X, the Cox ring Cox(X) is a Noetherian Z^n-graded normal domain for some n > 0. Let C(Cox(X)) be the cone (in R^n) which is spanned by the vectors a \in Z^n such that Cox(X)_a \neq 0. Then C(Cox(X)) is decomposed into a union of chambers. Berchtold and Hausen proved the existence of such decompositions for affine integral domains over an algebraically closed field. We shall give an elementary algebraic proof to this result in the case where the homogeneous component of degree 0 is a field. Using such decompositions, we develop the Demazure construction for Z^n-graded Kru…
The main result of this paper is a generalization of the theorem of Chevalley-Shephard-Todd to the rings of invariants of pseudoreflection groups over Dedekind domains. In the special case of a principal ideal domain in which the group order is invertible it is proved that this ring of invariants is isomorphic to a polynomial ring. An intermediate result is that every finitely generated regular graded algebra over a Dedekind domain is isomorphic to a tensor product of blowup algebras.
We prove the existence of HK density function for a pair $(R, I)$, where $R$ is a ${\mathbb N}$-graded domain of finite type over a perfect field and $I\subset R$ is a graded ideal of finite colength. This generalizes our earlier result where one proves the existence of such a function for a pair $(R, I)$, where, in addition $R$ is standard graded. As one of the consequences we show that if $G$ is a finite group scheme acting linearly on a polynomial ring $R$ of dimension $d$ then the HK density function $f_{R^G, {\bf m}_G}$, of the pair $(R^G, {\bf m}_G)$, is a piecewise polynomial function o…
Let $k$ be an algebraically closed field of characteristic 0, and $A$ a Cohen-Macaulay graded domain with $A_0=k$. If $A$ is semi-standard graded (i.e., $A$ is finitely generated as a $k[A_1]$-module), it has the $h$-vector $(h_0, h_1, ..., h_s)$, which encodes the Hilbert function of $A$. From now on, assume that $s=2$. It is known that if $A$ is standard graded (i.e., $A=k[A_1]$), then $A$ is level. We will show that, in the semi-standard case, if $A$ is not level, then $h_1+1$ divides $h_2$. Conversely, for any positive integers $h$ and $n$, there is a non-level $A$ with the $h$-vector $(1,…
Let $Γ$ be a torsionless commutative cancellative monoid, $R =\bigoplus_{α\in Γ}R_α$ be a $Γ$-graded integral domain, and $H$ be the set of nonzero homogeneous elements of $R$. In this paper, we show that if $Q$ is a maximal $t$-ideal of $R$ with $Q \cap H = \emptyset$, then $R_Q$ is a valuation domain. We then use this result to give simple proofs of the facts that (i) $R$ is a UMT-domain if and only if $R_Q$ is a quasi-Prüfer domain for each homogeneous maximal $t$-ideal $Q$ of $R$ and (ii) $R$ is a P$v$MD if and only if every nonzero finitely generated homogeneous ideal of $R$ is $t$-invert…
Almost Gorenstein standard graded rings and their localizations
本文证明了域上Cohen-Macaulay标准分次整环为几乎Gorenstein分次环，等价于其在分次极大理想处局部化的完备化为几乎Gorenstein局部环。
Let B be a commutative $\mathbb{Z}$-graded domain of characteristic zero. An element f of B is said to be cylindrical if it is nonzero, homogeneous of nonzero degree, and such that $B_{(f)}$ is a polynomial ring in one variable over a subring. We study the relation between the existence of a cylindrical element of B and the existence of a nonzero locally nilpotent derivation of B. Also, given d > 0, we give sufficient conditions that guarantee that every derivation of $B^{(d)} = \oplus_i B_{di}$ can be extended to a derivation of B. We generalize some results of Kishimoto, Prokhorov and Zaiden…
Let $G$ be a group with identity $e$. Let $R$ be a $G$-graded commutative ring and $M$ a graded $R$-module. In this paper, we introduce the concept of graded classical and graded strongly classical 2-absorbing second submodules of graded modules over a graded commutative rings. A number of results concerning these classes of graded submodules and their homogeneous components are given.
A characterization of monoid graded semihereditary rings
研究了格子左半赫瑞迪环的特征，证明了格子左合意性和所有平坦左模子模的平坦性是充要条件，从而给出了格子普鲁弗域的新特征。
Rigidity of Graded Integral Domains and of their Veronese Subrings
研究分次整环的刚性是否遗传给其Veronese子环，以及子环的导子能否扩展到原环，刻画使Veronese子环非刚性的子群性质。
The space of homogeneous preserving semistar operations on graded domains
本文研究分次整环上保持齐次性的半星运算空间，证明 $\star_a$ 保持齐次性，并证明齐次 Kronecker 函数环的赋值超环集合与分次赋值超环集合同胚，以及有限型保持齐次性的半星运算集合构成谱空间。
On monoid graded semihereditary rings
研究分级左赫瑞德和左半赫瑞德环的模块性质，提供分级自由、投射、注入和平坦模块的分级版本，包括巴尔准则和拉兹洛定理。
Let $I$ be an ideal generated by a system of parameters in an excellent Cohen-Macaulay local domain. We show that the associated graded ring $G^*(I)$ of the filtration $\{(I^n)^*: n\in \mathbb{N}\}$ is Cohen-Macaulay. We prove that if $R$ is an excellent Buchsbaum local domain then $G^*(I)$ is a Buchsbaum module over the Rees ring $\mathcal R^*(I)=\oplus_{n\in \mathbb{N}}(I^n)^*.$ We provide quick proofs of well-known results of I. Aberbach, Huneke-Itoh and Huneke-Hochster about the filtration $\{(I^n)^*: n\in \mathbb{N}\}$ in excellent local domains. An important tool used in the proofs is a …
We shall describe the divisor class group and the graded canonical module of the multi-section ring for a normal projective variety X and Weil divisors D_1,..., D_s on X under a mild condition. In the proof, we use the theory of Krull domain and the equivariant twisted inverse functor due to Hashimoto.
We demonstrate how some classical computations of divisor class groups can be obtained using the theory of rational coefficient Weil divisors and related results of Watanabe.
Stability theorems for positively graded domains and a question of Lindel
本文证明正分次诺特整环中单模行可补成同伦于单位阵的可逆矩阵，由此得出生成元提升、射影模分裂及Lindel问题的肯定解答，并给出射影模可消去性的充分条件。
When do pseudo-Gorenstein rings become Gorenstein?
本文研究伪Gorenstein环成为Gorenstein环的条件，证明在温和假设下伪Gorenstein的近乎Gorenstein分次整环必为Gorenstein，并阐明相关概念关系及给出构造拟Gorenstein环的方法。
We give examples of two dimensional normal ${\mathbb Q}$-Gorenstein graded domains, where the set of $F$-thresholds of the maximal ideal is not discrete, thus answering a question by Mustaţă-Takagi-Watanabe. We also prove that, for a two dimensional standard graded domain $(R, {\bf m})$ over a field of characteristic $0$, with graded ideal $I$, if $({\bf m}_p, I_p)$ is a reduction mod $p$ of $({\bf m}, I)$ then $c^{I_p}({\bf m}_p) \neq c^I_{\infty}({\bf m})$ implies $c^{I_p}({\bf m}_p)$ has $p$ in the denominator.
We define graded group schemes and graded group varieties and develop their theory. Graded group schemes are the graded analogue of group schemes and are in correspondence with graded Hopf algebra. In this setting, graded group varieties take the place of infinitesimal group schemes; an important and well studied class of group schemes. We give some examples, derive their properties, and define some special type of graded group schemes, like connected and étale graded group schemes, among others. We give a generalization of the result that connected graded bialgebras are graded Hopf algebra. O…
We prove that a complete local or graded one-dimensional domain of prime characteristic has finite F-representation type if its residue field is algebraically closed or finite, and present examples of a complete local or graded one-dimensional domain which does not have finite F-representation type with a perfect residue field. We also present some examples of higher dimensional rings of finite F-representation type.
Let $A$ be a regular domain containing a field $K$ of characteristic zero, $G$ be a finite subgroup of the group of automorphisms of $A$ and $B=A^G$ be the ring of invariants of $G$. Let $S= A[X_1,\ldots, X_m]$ and $R= B[X_1, \ldots, X_m]$ be standard graded with $\ deg \ A=0$, $\ deg \ B=0$ and $\ deg \ X_i=1$ for all $i$. Extend the action of $G$ on $A$ to $S$ by fixing $X_i$. Note $S^G=R$. Let $I$ be an arbitrary homogeneous ideal in $R$. The main goal of this paper is to establish a comparative study of graded components of local cohomology modules $H_I^i(R)$ that would be analogs to those…
Density functions for filtrations of graded ideals
本文发展了标准分次整环上任意分次理想滤链的密度函数一般理论，证明其基本性质、分段多项式逼近与饱和密度函数的可微性，并给出符号幂与整闭包重合的数值判据及混合重数不等式。
Suppose that R\rightarrow S is an extension of local domains and ν^* is a valuation dominating S. We consider the natural extension of associated graded rings along the valuation gr_{ν^*}(R)\rightarrow gr_{ν^*}(S). We give examples showing that in general, this extension does not share good properties of the extension $\rightarrow S, but after enough blow ups above the valuations, good properties of the extension R\rightarrow S are reflected in the extension of associated graded rings. Stable properties of this extension (after blowing up) are much better in characteristic zero than in positiv…
On graded u-nil clean rings
该文定义并研究分次 U-nil 洁净环，作为分次 nil-good 环的推广，并讨论其在矩阵环、分次群环及平凡环扩张中的性质转移。
We consider $\G$-graded commutative algebras, where $\G$ is an abelian group. Starting from a remarkable example of the classical algebra of quaternions and, more generally, an arbitrary Clifford algebra, we develop a general viewpoint on the subject. We then give a recent classification result and formulate an open problem.
Let $G$ be a group with identity $e$. Let $R$ be a $G$-graded commutative ring, $M$ a graded $R$-module and $A\subseteq h(R)$ a multiplicatively closed subset of $R$. In this paper, we introduce the concept of graded $A$-2-absorbing submodules of $M$ as a generalization of graded 2-absorbing submodules and graded $A$-prime submodules of $M.$ We investigate some properties of this class of graded submodules.
In this paper we show that the sets of $F$-jumping coefficients of ideals form discrete sets in certain graded $F$-finite rings. We do so by giving a criterion based on linear bounds for the growth of the Castelnuovo-Mumford regularity of certain ideals. We further show that these linear bounds exists for one-dimensional rings and for ideals of (most) two-dimensional domains. We conclude by applying our technique to prove that all sets of $F$-jumping coefficients of all ideals in the determinantal ring given as the quotient by $2\times 2$ minors in a $2\times 3$ matrix of indeterminates form d…
Let k be a field of any characteristic and R = k[x,y,z]/(f) be a graded normal hypersurface. We call (a,b,c; h) = deg(x,y,z;f) the type of R with gcd(a,b,c)=1. Then the a-invariant a(R) is given by h - (a+b+c). The classification of such R (or f) was made by many authors (Arnold, Saito, Wagreich, ...). Here we classify the possible types of R for a fixed a(R) with $- 1 \le a(R) \le 6$ by commutative ring theoretic method using the Dolgachev-Pinkham-Demazure construction of normal graded rings. We also show that if we fix $a(R) \ge 0$, then the number of possible types of R is finite.
We prove that, if $A$ is a positively graded, graded commutative, local, finite Hopf algebra, its cohomology is finitely generated, thus unifying classical results of Wilkerson and Hopkins-Smith, and of Friedlander-Suslin. We do this by showing the existence of conormal elementary quotients.
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