$v$-numbers of symbolic power filtrations

Abstract

We study the asymptotic behaviour of $v$-number and local $v$-numbers of Noetherian generalized symbolic power filtrations $\mathcal I=\{I_n\}$ in a Noetherian $\mathbb N$-graded domain and show that they are quasi-linear type. We provide sufficient conditions for the existence of the limits $\lim\limits_{n\to\infty}\frac{v(I_n)}{n}$ and $\lim\limits_{n\to\infty}\frac{v_\mathfrak p(I_n)}{n}$ for all $\mathfrak p\in\overline A(\mathcal I)$. We explicitly compute local $v$-numbers and $v$-numbers of symbolic powers of cover ideals of complete bipartite graphs, complete graphs, cycles, $K_m^s$ and compare them with their Castelnuovo-Mumford regularity. We give an example of a bipartite graph $\mathcal H$ that is not a complete bipartite graph and $v(J(\mathcal H))>bight(I(\mathcal H))-1$. This answers a question in [25, Question 3.12]. We show that for both connected bipartite graphs and connected non-bipartite graphs, the difference between the regularity and the $v$-number of the cover ideals can be arbitrarily large. This strengthens and gives an alternative proof of[25,Theorem 3.10]. We provide a counterexample to a conjecture [12, Conjecture 5.4] due to A. Ficarra and E. Sgroi.