On the defining equations of Rees algebra of a height two perfect ideal using the theory of $D$-modules

Abstract

Let $k$ be a field of characteristic zero, and $R=k[x_1, \ldots, x_d]$ with $d \geq 3$ be a polynomial ring in $d$ variables. Let $\m=(x_1, \ldots, x_d)$ be the homogeneous maximal ideal of $R$. Let $\mathcal{K}$ be the kernel of the canonical map $\alpha: \sym(I) \rightarrow \R(I)$, where $\sym(I)$ (resp. $\R(I)$) denotes the symmetric algebra (resp. the Rees algebra) of an ideal $I$ in $R$. We study $\mathcal{K}$ when $I$ is a height two perfect ideal minimally generated by $d+1$ homogeneous elements of same degree and satisfies $G_d$, that is, the minimal number of generators of the ideal $I_{\mathfrak{p}}$, $\mu(I_{\mathfrak{p}}) \leq \dim R_{\mathfrak{p}}$ for every $\mathfrak{p} \in V(I) \backslash \{\m\}$. We show that \begin{enumerate}[{\rm (i)}] \item $\mathcal{K}$ can be described as the solution set of a system of differential equations, \item the whole bigraded structure of $\mathcal{K}$ is characterized by the integral roots of certain $b$-functions, \item certain de Rham cohomology groups can give partial information about $\mathcal{K}$. \end{enumerate}