arXiv subjects
Publications and source records attributed to Parviz Sahandi.
Let $\Gamma$ be a cancellation monoid and $R=\bigoplus_{\alpha \in \Gamma}R_{\alpha}$ be a $\Gamma$-graded ring. It is shown that $R$ is graded left semihereditary if and only if $R$ is graded left coherent and every graded submodule of a flat left $R$-module is flat. Hence it gives a new characterization of graded-Pr\"{u}fer domains.
In order to study graded left hereditary and left semihereditary rings graded by a cancelation monoid in terms of their modules, we need to revisit graded free, projective, injective, and flat modules and provide graded versions of specific results concerning these modules, like Baer's criterion on injectivity and Lazard's theorem on flatness. Then, among other things, we can give some characterization of graded left hereditary and left semihereditary rings, in particular, of graded-Pr\"{u}fer and graded-Dedekind domains.
In this paper we consider the graded going-down property of graded integral domains in pullbacks. It then enables us to give original examples of these domains.
Let $R=\bigoplus_{\alpha\in\Gamma}R_{\alpha}$ be a graded integral domain. In this paper we study the space of homogeneous preserving semistar operations on $R$. We show if $\star$ is a homogeneous preserving semistar operation on $R$, then $\star_a$ is also homogeneous preserving. Let $KR(R,b)$ be the homogeneous Kronecker function ring of $R$ with respect to the $b$-operation. It is shown that the set of valuation overrings of $KR(R,b)$, endowed with the Zariski topology, is homeomorphism to $Zar_h(R)$, the set of gr-valuation overrings of $R$, endowed with the Zariski topology. We also show that the set $SStar_{f,hp}(R)$ of finite type, homogeneous preserving semistar operations on $R$, endowed with the Zariski topology, is a spectral space.
Let $\Gamma$ be a torsionless commutative cancellative monoid, $R=\bigoplus_{\alpha \in \Gamma}R_{\alpha}$ be a $\Gamma$-graded integral domain. In this note we show that each homogeneous star operation $\star:\mathbf{HF}(R)\to\mathbf{HF}(R)$ of $R$, is the restriction of a (classical) star operation $e(\star):F(R)\to F(R)$ of $R$. We also show that the set $HStar_f(R)$ of homogeneous star operations of finite type on $R$, endowed with the Zariski topology, is a spectral space.
Let $\Gamma$ be a torsionless commutative cancellative monoid and $R =\bigoplus_{\alpha \in \Gamma}R_{\alpha}$ be a $\Gamma$-graded integral domain. In this paper, we introduce the notion of graded going-down domains. Among other things, we provide an equivalent condition for graded-Pr\"{u}fer domains in terms of graded going-down and graded finite-conductor domains. We also characterize graded going-down domains by means of graded divided domains. As an application, we show that the graded going-down property is stable under factor domains.
We introduce new homological dimensions, namely the Cohen-Macaulay projective, injective and flat dimensions for homologically bounded complexes. Among other things we show that (a) these invariants characterize the Cohen-Macaulay property for local rings, (b) Cohen-Macaulay flat dimension fits between the Gorenstein flat dimension and the large restricted flat dimension, and (c) Cohen-Macaulay injective dimension fits between the Gorenstein injective dimension and the Chouinard invariant.
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 $t$-invertible, if and only if $R_Q$ is a valuation domain for all homogeneous maximal $t$-ideals $Q$ of $R$. Let $D[Γ]$ be the monoid domain of $Γ$ over an integral domain $D$. We also show that $D[Γ]$ is a UMT-domain if and only if $D$ is a UMT-domain and the integral closure of $Γ_S$ is a valuation monoid for all maximal $t$-ideals $S$ of $Γ$. Hence, $D[Γ]$ is a P$v$MD if and only if $D$ is a P$v$MD and $Γ$ is a P$v$MS.
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 $\NA(D,\star)$ is a Prüfer domain if and only if $\NA(R,\star)$ is a Bézout domain. We also determine when $\NA(R,v)$ is a PID.
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 $\star$-multiplication domain. In particular we give new characterizations for a graded integral domain, to be a P$v$MD.
There are nice relations between graded homological dimensions and ordinary homological dimensions. We study the Gorenstein injective dimension of a complex of graded modules denoted by $^*\Gid$, and derive its properties. In particular we prove the Chouinard's like formula for $^*\Gid$, and compare it with the usual Gorenstein injective dimension.
In this note we show that an integral domain $D$ of finite $w$-dimension is a quasi-Prüfer domain if and only if each overring of $D$ is a $w$-Jaffard domain. Similar characterizations of quasi-Prüfer domains are given by replacing $w$-Jaffard domain by $w$-stably strong S-domain, and $w$-strong S-domain. We also give new characterizations of UM$t$ domains.
In this paper we study the class of $w$-Jaffard domains in pullback constructions, and give new examples of these domains. In particular we give examples to show that the two classes of $w$-Jaffard and Jaffard domains are incomparable. As another application, we establish that for each pair of positive integers $(n,m)$ with $n+1\leq m\leq 2n+1$, there is an (integrally closed) integral domain $R$ such that $w$-$\dim(R)=n$ and $w[X]$-$\dim(R[X])=m$.
We prove the depth formula, for homologically bounded complexes $X, Y$ provided that the complete intersection flat dimension of $X$ is finite and $\sup(X\utp_RY)<\infty$. In particular, let $M$ and $N$ are two $R$-modules and the complete intersection flat dimension of $M$ is finite. Then $M$ and $N$ satisfies the depth formula, provided $\Tor^R_i(M,N)=0$ for all $i\ge 1$.
Let $D$ be an integral domain and $\star$ a semistar operation stable and of finite type on it. In this paper we define the semistar dimension (inequality) formula and discover their relations with $\star$-universally catenarian domains and $\star$-stably strong S-domains. As an application we give new characterizations of $\star$-quasi-Prüfer domains and UM$t$ domains in terms of dimension inequality formula (and the notions of universally catenarian domain, stably strong S-domain, strong S-domain, and Jaffard domains). We also extend Arnold's formula to the setting of semistar operations.
Given a stable semistar operation of finite type $\star$ on an integral domain $D$, we show that it is possible to define in a canonical way a stable semistar operation of finite type $\star[X]$ on the polynomial ring $D[X]$, such that, if $n:=\star$-$\dim(D)$, then $n+1\leq \star[X]\text{-}\dim(D[X])\leq 2n+1$. We also establish that if $D$ is a $\star$-Noetherian domain or is a Prüfer $\star$-multiplication domain, then $\star[X]\text{-}\dim(D[X])=\star\text{-}\dim(D)+1$. Moreover we define the semistar valuative dimension of the domain $D$, denoted by $\star$-$\dim_v(D)$, to be the maximal rank of the $\star$-valuation overrings of $D$. We show that $\star$-$\dim_v(D)=n$ if and only if $\star[X_1,...,X_n]$-$\dim_v(D[X_1,...,X_n])=2n$, and that if $\star$-$\dim_v(D)<\infty$ then $\star[X]$-$\dim_v(D[X])=\star$-$\dim_v(D)+1$. In general $\star$-$\dim(D)\leq\star$-$\dim_v(D)$ and equality holds if $D$ is a $\star$-Noetherian domain or is a Prüfer $\star$-multiplication domain. We define the $\star$-Jaffard domains as domains $D$ such that $\star$-$\dim(D)<\infty$ and $\star$-$\dim(D)=\star$-$\dim_v(D)$. As an application, $\star$-quasi-Prüfer domains are characterized as domains $D$ such that each $(\star,\star')$-linked overring $T$ of $D$, is a $\star'$-Jaffard domain, where $\star'$ is a stable semistar operation of finite type on $T$. As a consequence of this result we obtain that a Krull domain $D$, must be a $w_D$-Jaffard domain.
Let $R$ be a commutative integral domain and let $\star$ be a semistar operation of finite type on $R$, and $I$ be a quasi-$\star$-ideal of $R$. We show that, if every minimal prime ideal of $I$ is the radical of a $\star$-finite ideal, then the set $\Min(I)$ of minimal prime ideals over $I$ is finite.
Let $D$ be an integral domain and $\star$ a semistar operation stable and of finite type on it. In this paper, we are concerned with the study of the semistar (Krull) dimension theory of polynomial rings over $D$. We introduce and investigate the notions of $\star$-universally catenarian and $\star$-stably strong S-domains and prove that, every $\star$-locally finite dimensional Prüfer $\star$-multiplication domain is $\star$-universally catenarian, and this implies $\star$-stably strong S-domain. We also give new characterizations of $\star$-quasi-Prüfer domains introduced recently by Chang and Fontana, in terms of these notions.