arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2501.01807math.AGmath.ACmath.CO
收藏

关于与自由性相关的平面曲线的若干评注

Some remarks on plane curves related to freeness

Alexandru Dimca

AI总结:

本文研究非自由复射影平面曲线下自由曲线相关公式的变化,证明任意曲线的庞加莱多项式与贝蒂多项式之差为特定多项式,并给出直线排列第二指数的新界,改进了相关已有结果。

摘要:

设$C$为一条既约复射影平面曲线,$d_1$与$d_2$为$C$的前两个最小指数。对于次数为$d$的自由曲线$C$,存在一个联系$d,d_1, d_2$与$C$的总Tjurina数的简单公式。我们的第一个结果讨论了当曲线$C$不再自由时该结果的变化情况。对于自由直线排列,其庞加莱多项式与贝蒂多项式$B(t)$一致,也与乘积$P(t)=(1+d_1t)(1+d_2t)$一致。我们的第二个结果表明,对于任意曲线$C$,差值$P(t)-B(t)$是一个多项式$a t +bt^2$,其中$a$与$b$为非负整数。此外,$a =0$或$b=0$当且仅当$C$是自由直线排列。最后,我们给出了直线排列$\mathcal A$的第二指数$d_2$的新界,其对应的下界改进了H. Schenck关于$\mathcal A$的最大指数与$\mathcal A$中点的最大重数之间关系的一个结果。

英文摘要:

Let $C$ be a reduced complex projective plane curve, and let $d_1$ and $d_2$ be the first two smallest exponents of $C$. For a free curve $C$ of degree $d$, there is a simple formula relating $d,d_1, d_2$ and the total Tjurina number of $C$. Our first result discusses how this result changes when the curve $C$ is no longer free. For a free line arrangement, the Poincaré polynomial coincides with the Betti polynomial $B(t)$ and with the product $P(t)=(1+d_1t)(1+d_2t)$. Our second result shows that for any curve $C$, the difference $P(t)-B(t)$ is a polynomial $a t +bt^2$, with $a$ and $b$ non-negative integers. Moreover $a =0$ or $b=0$ if and only if $C$ is a free line arrangement. Finally we give new bounds for the second exponent $d_2$ of a line arrangement $\mathcal A$, the corresponding lower bound being an improvement of a result by H. Schenck concerning the relation between the maximal exponent of $\mathcal A$ and the maximal multiplicity of points in $\mathcal A$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑