Jakub Kabat
The main purpose of the present paper is to study the numerical properties of supersolvable resolutions of line arrangements. We provide upper-bounds on the so-called extension to supersolvability numbers for certain extreme line arrangements in $\mathbb{P}^{2}_{\mathbb{C}}$ and we show that these numbers \textbf{are not} determined by the intersection lattice of the given arrangement.
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We study supersolvable line arrangements in ${\mathbb P}^2$ over the reals and over the complex numbers, as the first step toward a combinatorial classification. Our main results show that a nontrivial (i.e., not a pencil or near pencil) complex line arrangement cannot have more than 4 modular points, and if all of the crossing points of a complex line arrangement have multiplicity 3 or 4, then the arrangement must have 0 modular points (i.e., it cannot be supersolvable). This provides at least a little evidence for our conjecture that every nontrivial complex supersolvable line arrangement ha…
We show that the number of lines in an $m$--homogeneous supersolvable line arrangement is upper bounded by $3m-3$ and we classify the $m$--homogeneous supersolvable line arrangements with two modular points up-to lattice-isotopy. A lower bound for the number of double points $n_2$ in an $m$--homogeneous supersolvable line arrangement of $d$ lines is also considered. When $3 \leq m \leq 5$, or when $m \geq \frac{d}{2}$, or when there are at least two modular points, we show that $n_2 \geq \frac{d}{2}$, as conjectured by B. Anzis and S. O. Toh\u aneanu. This conjecture is shown to hold also for …
We introduce a new class of line arrangements in the projective plane, called nearly supersolvable, and show that any arrangement in this class is either free or nearly free. More precisely, we show that the minimal degree of a Jacobian syzygy for the defining equation of the line arrangement, which is a subtle algebraic invariant, is determined in this case by the combinatorics. When such a line arrangement is nearly free, we discuss the splitting types and the jumping lines of the associated rank two vector bundle, as well as the corresponding jumping points, introduced recently by S. Marche…
In this paper we give a very natural description of the bijections between the minimal CW-complex homotopy equivalent to the complement of a supersolvable arrangement $\mathcal{A}$, the $\textbf{nbc}$ basis of the Orlik-Solomon algebra associated to $\mathcal{A}$ and the set of chambers of $\mathcal{A}$. We use these bijections to get results on the first (co)homology group of the Milnor fiber of $\mathcal{A}$ and to describe a bijection between the symmetric group and the $\textbf{nbc}$ basis of the braid arrangement.
We prove Anzis and Tohaneanu conjecture, that is the Dirac-Motzkin conjecture for supersolvable line arrangements in the projective plane over an arbitrary field of characteristic zero. Moreover, we show that a divisionally free arrangements of lines contain at least one double point, that can be regarded as the Sylvester-Gallai theorem for some free arrangements. This is a corollary of a general result that if you add a line to a free projective line arrangement, then that line has to contain at least one double point. Also we prove some conjectures and one open problems related to supersolva…
In a recent paper arXiv:1602.02300v2, Cook II, Harbourne, Migliore and Nagel related the splitting type of a line arrangement in the projective plane to the number of conditions imposed by a general fat point of multiplicity $j$ to the linear system of curves of degree $j+1$ passing through the configuration of points dual to the given arrangement. If the number of conditions is less than the expected, we say that the configuration of points admits unexpected curves. In this paper, we characterize supersolvable line arrangements whose dual configuration admits unexpected curves and we provide …
For a line arrangement in the complex projective plane $\mathbb{P}^2$, we investigate the compactification $\overline{F}$ of the affine Milnor fiber in $\mathbb{P}^3$ and its minimal resolution $\widetilde{F}$. We compute the Chern numbers in terms of the combinatorics of the line arrangement, then we show that the minimal resolution is never a quotient of a ball; in addition, we also prove that $\widetilde{F}$ is of general type when the arrangement has only nodes or triple points as singularities.
If $M$ is the complement of a hyperplane arrangement, and $A=H^*(M,\k)$ is the cohomology ring of $M$ over a field of characteristic 0, then the ranks, $ϕ_k$, of the lower central series quotients of $π_1(M)$ can be computed from the Betti numbers, $b_{ii}=\dim_{\k} \Tor^A_i(\k,\k)_i$, of the linear strand in a (minimal) free resolution of $\k$ over $A$. We use the Cartan-Eilenberg change of rings spectral sequence to relate these numbers to the graded Betti numbers, $b'_{ij}=\dim_{\k} \Tor^E_i(A,\k)_j$, of a (minimal) resolution of $A$ over the exterior algebra $E$. From this analysis, we rec…
In this paper we construct 206 examples of Calabi-Yau manifolds with different Euler numbers. All constructed examples are smooth models of double coverings of $P^3$ branched along an octic surface. We allow 11 types of (not necessary isolated) singularities in the branch locus. Thus we broaden the class of examples studied in math.AG/9902057. For every considered example we compute the Euler number and give a precise description of a resolution of singularities.
A penalised Saito functional for heuristic search of free line arrangements
本文提出一种非负功能，用于衡量线束的自由性，通过半连续松弛Saito准则，利用角度最小化方法实现自由性的计算探索。
On the Jacobian algebras of Ziegler pairs of plane arrangements
研究Ziegler平面排列对的雅可比代数的贝蒂数差异及其与二维线排列Ziegler对的锥面关系
Free resolution of the logarithmic derivation modules of close to free arrangements
该文研究从自由构形删除两个超平面得到的接近自由构形的对数导子模结构，给出其极小自由分解信息与分次Betti数下界，确定三维情形的极小自由分解并辅以示例揭示代数与组合性质的关联。
Construction of free curves by adding lines to a given curve
本文通过添加特定直线构造新的自由平面曲线，提出超可解曲线猜想，并给出度8和度9的极大曲线新例子，以及自由圆锥线排列的构造。
First we construct a free resolution for the Milnor (or Jacobian) algebra $M(f)$ of a complex projective Chebyshev plane curve $\CC_d:f=0$ of degree $d$. In particular, this resolution implies that the dimensions of the graded components $M(f)_k$ are constant for $k \geq 2d-3.$ Then we show that the Milnor algebra of a nodal plane curve $C$ has such a behaviour if and only if all the irreducible components of $C$ are rational. For the Chebyshev curves, all of these components are in addition smooth, hence they are lines or conics and explicit factorizations are given in this case.
We show that if X is the complement of a complex hyperplane arrangement, then the homology of X has linear free resolution as a module over the exterior algebra on the first cohomology of X. We study invariants of X that can be deduced from this resolution. A key ingredient is a result of Aramova, Avramov, and Herzog [2000] on resolutions of monomial ideals in the exterior algebra. We give a new conceptual proof of this result.
A minimal resolution for the Jacobian ideal of a generic curve arrangement
本文利用似然对应理论，为复射影平面中节点曲线排列的雅可比理想的第一、第二合冲模构造了显式极小生成元集，并推广到超曲面排列情形。
A Resolution of the Diagonal for Smooth Projective Toric Varieties
研究光滑射影环面簇在主除子格条件不成立时的对角线分解问题，通过阶梯函数标记顶点并施加扇形对称假设，得到\(X_\Sigma\times X_\Sigma\)上\(\mathcal{O}_\Delta\)的局部自由分解，还探讨了变形参数\(\epsilon\)对分解族的影响。
Let $ \mathcal{D} = \{D_{1}, \ldots, D_{\ell}\} $ be an arrangement of smooth hypersurfaces with normal crossings on the complex projective space $ \mathbb{P}^{n} $ and let $ Ω^{1}_{\mathbb{P}^{n}}(log \mathcal{D}) $ be the logarithmic bundle attached to it. Our aim is to study the injectivity of the correspondence $ \mathcal{D} \longrightarrow Ω^{1}_{\mathbb{P}^{n}}(log \mathcal{D}) $. In order to do that, we first show that $ Ω^{1}_{\mathbb{P}^{n}}(log \mathcal{D}) $ admits a resolution of length $ 1 $ depending on the degrees and on the equations of $ D_{1}, \ldots, D_{\ell} $. Then, we pro…
A collection $S = \{D_1,\ldots, D_n\}$ of divisors in a smooth variety $X$ is an {\em arrangement} if intersections of all subsets of $S$ are smooth. We show that a double cover of $X$ ramified on an arrangement has a crepant resolution under additional hypotheses. Namely, we assume that all intersection components that change the canonical divisor when blown up satisfy are {\em splayed}, a property of the tangent spaces of the components first studied by Faber. This strengthens a result of Cynk and Hulek, which requires a stronger hypothesis on the intersection components. Further, we study t…
In this note we describe the minimal resolution of the ideal $I_f$, the saturation of the Jacobian ideal of a nearly free plane curve $C:f=0$. In particular, it follows that this ideal $I_f$ can be generated by at most 4 polynomials. Related general results by Hassanzadeh and Simis on the saturation of codimension 2 ideals are discussed in detail. Some applications to rational cuspidal plane curves and to line arrangements are also given.
On the numerical Terao's conjecture and Ziegler pairs for line arrangements
本文提出了一个反例，反驳了复射影平面上线束安排中的数值Terao猜想，并构造了具有相同底层matroid但不同自由解析的Ziegler对。
Let $G$ be a group which admits the structure of an iterated semidirect product of finitely generated free groups. We construct a finite, free resolution of the integers over the group ring of $G$. This resolution is used to define representations of groups which act compatibly on $G$, generalizing classical constructions of Magnus, Burau, and Gassner. Our construction also yields algorithms for computing the homology of the Milnor fiber of a fiber-type hyperplane arrangement, and more generally, the homology of the complement of such an arrangement with coefficients in an arbitrary local syst…
Given $Σ\subset R:=\mathbb K[x_1,\ldots,x_k]$, where $\mathbb K$ is a field of characteristic 0, any finite collection of linear forms, some possibly proportional, and any $1\leq a\leq |Σ|$, we prove that $I_a(Σ)$, the ideal generated by all $a$-fold products of $Σ$, has linear graded free resolution. This allows us to determine a generating set for the defining ideal of the Orlik-Terao algebra of the second order of a line arrangement in $\mathbb P_{\mathbb{K}}^2$, and to conclude that for the case $k=3$, and $Σ$ defining such a line arrangement, the ideal $I_{|Σ|-2}(Σ)$ is of fiber type. We …
Topological inequalities for conic-line arrangements with some prescribed singularities
该研究从4维流形视角引入组合二次曲线-直线构形，证明了ADE型偶总次数构形的Hirzebruch型不等式，还通过相关理论得到可分与奇数型构形消解重数序列的不等式与同余式。
On Ziegler pairs of line arrangements: from non-existence to abundance
研究线排列的Ziegler对，证明当线数d<9时交格决定指数数据，并列举d=10时的六个不同Ziegler对，构造了具有相同交格、雅可比关系最小次数和Milnor代数希尔伯特函数但不同最小分级自由分解的高次例子。
From Pascal's Theorem to the geometry of Ziegler's line arrangements
本文研究 Ziegler 与 Yuzvinsky 用以说明同调不变量和形式性不由组合学决定的六边形线排布，揭示其与帕斯卡定理的几何联系，并给出 Jacobian syzygy 最小次数及形式性的一般结论。
Small resolutions of moduli spaces of scaled curves
本文提出了一种方法，用于构造稳定缩放n标记直线和有理树的模空间的小解析扩张，并探讨了其与图矩阵的关系。
Resolutions of Type $\mathbb{A}$ Quantum Surface Singularities
本文通过构造几何解析类别\mathcal{X}，展示了类型A量子克莱因奇点的非交换解析与导出等价性，并推广了经典克莱因奇点的几何 McKay对应。
On the Jacobian syzygies for generic toric models
本文针对仿射环面中的一般超曲面，在射影空间关联超曲面配置，并计算了相应雅可比代数的最小分次分解。
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