Semistar-Krull and Valuative Dimension of Integral Domains

Abstract

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.