Singular Loci of Hibi toric varieties
V. Lakshmibai, H. Mukherjee
我们首先在Hibi复曲面簇上的奇点处构造余切空间的显式基，即，与分配格有关的复曲面簇。然后，我们确定这些环面品种的奇异轨迹。
We first construct explicit bases for the cotangent spaces at singular points on Hibi toric varieties, i.e., toric varieties associated to distributive lattices. We then determine the singular loci of these toric varieties.
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Singular loci of Bruhat-Hibi toric varieties
对于复曲面簇X关联的布鲁哈特偏序集的舒伯特品种在一个极小的G/P，我们描述的奇异轨迹相关联的多面体锥的面孔。我们进一步证明了X中的奇异轨迹是纯余维数为3的。
We compute the divisor class group and the Picard group of projective varieties with Hibi rings as homogeneous coordinate rings. These varieties are precisely the toric varieties associated to order polytopes. We use tools from the theory of toric varieties to get a description of the two groups which only depends on combinatorial properties of the underlying poset.
In this article, we summarize combinatorial description of complete intersection Calabi-Yau threefolds in Hibi toric varieties. Such Calabi-Yau threefolds have at worst conifold singularities, and are often smoothable to non-singular Calabi-Yau threefolds. We focus on such non-singular Calabi-Yau threefolds of Picard number one, and illustrate the calculation of topological invariants, using new motivating examples.
Singular loci of Grassmann-Hibi toric varieties
对于复曲面簇X与Schubert簇的Bruhat偏序集在格拉斯曼，我们描述了奇异轨迹的相关多面体锥的面。我们还确定了X的最大奇点处的切锥。这些又是复曲面的变种。在n维向量空间（基域上）中2-平面格拉斯曼的Schubert簇的Bruhat偏序集上，我们还证明了一个与某些奇点处的重数有关的乘积公式.
We describe the non-Gorenstein loci of normal toric varieties. In the case of Hibi rings a combinatorial description is provided in terms of the underlying partially ordered set. As a non-toric application we compute the dimensions of the non-Gorenstein loci of the first secant variety of Segre varieties.
Conic divisorial ideals of toric rings and applications to Hibi rings and stable set rings
本文研究环面环的锥除子理想，提出确定方法并描述了完美图的Hibi环与稳定集环的锥除子理想，刻画了其对称性，并构造了特殊稳定集环族的NCCR。
In this paper, we study splitting (or toric) non-commutative crepant resolutions (= NCCRs) of some toric rings. In particular, we consider Hibi rings, which are toric rings arising from partially ordered sets, and show that Gorenstein Hibi rings with class group $\mathbb{Z}^2$ have a splitting NCCR. In the appendix, we also discuss Gorenstein toric rings with class group $\mathbb{Z}$, in which case the existence of splitting NCCRs is already known. We especially observe the mutations of modules giving splitting NCCRs for the three dimensional case, and show the connectedness of the exchange gr…
In this manuscript we sharpen the lower bound on the codimension of the irreducible components of the Noether-Lefschetz locus of surfaces in projective toric threefolds given in [BG17]. We also provide a simpler proof of Theorem 4.11 in [BG17], which allows one to avoid some technical assumptions.
Stable base loci, movable curves, and small modifications, for toric varieties
我们证明了在一个完全Q-阶乘复曲面簇X上的因子锥的对偶是由其稳定基轨迹的维数小于k的小修改曲线生成的，这些修改曲线在族中移动，从而扫除了X的k维子簇的双有理变换。我们给出了一个例子，表明它不足以考虑X本身的曲线。
We study the real loci of toric degenerations of complex varieties with reducible central fibre. We show that the topology of such degenerations can be explicitly described via the Kato-Nakayama space of the central fibre as a log space. We furthermore provide generalities of real structures in log geometry and their lift to Kato-Nakayama spaces. A key point of this paper is a description of the Kato-Nakayama space of a toric degeneration and its real locus, both as bundles determined by combinatorial data. We provide several examples including real toric degenerations of K3-surfaces and a tor…
We study equivariant bi-vector fields on a toric variety. We prove that, on a smooth toric variety of dimension $n$, the locus where the rank of an equivariant bi-vector field is $\leq 2k$ is not empty and has at least a component of dimension $\geq 2k+1$, for all integers $k> 0$ such that $2k < n$. The same is true also for $k=0$, if the toric variety is smooth and compact. While for the non compact case, the locus in question has to be assumed to be non empty.
We construct a family of flat semitoric degenerations for the Hibi variety of every finite distributive lattice. The irreducible components of each degeneration are the toric varieties associated with polytopes forming a regular subdivision of the order polytope of the underlying poset. These components are themselves Hibi varieties. For each degeneration in our family we also define the corresponding weight polytope and embed the degeneration into the associated toric variety as the union of orbit closures given by a set of faces. Every such weight polytope projects onto the order polytope wi…
We continue our study of the Noether-Lefschetz loci in toric varieties and investigate deformation of pairs (V,X) where V is a complete intersection subvariety and X a quasi-smooth hypersurface in a odd dimensional simplicial projective toric variety, with V\subset X. Under some assumptions, we prove that the cohomological class in H^{k,k}(X) associated to V remains of type (k,k) under an infinitesimal deformation if and only if V remains algebraic. Actually we prove that locally the Noether-Lefschetz locus is an irreducible component of a suitable Hilbert scheme. This generalizes Theorem 4.2 …
The notion of a d-critical locus is an ingredient in the definition of motivic Donaldson-Thomas invariants by [BJM19]. There is a canonical d-critical locus structure on the Hilbert scheme of dimension zero subschemes on local toric Calabi-Yau 3-folds. This is obtained by truncating the $-1$-shifted symplectic structure on the derived moduli stack [BBBBJ15]. In this paper we show the canonical d-critical locus structure has critical charts consistent with the description of Hilbert scheme as a degeneracy locus [BBS13]. In particular, the canonical d-critical locus structure is isomorphic to th…
We study the base locus of the higher fundamental forms of a projective toric variety $X$ at a general point. More precisely we consider the closure $X$ of the image of a map $({\mathbb C}^*)^k\to {\mathbb P}^n$, sending $t$ to the vector of Laurent monomials with exponents $p_0,\dots,p_n\in {\mathbb Z}^k$. We prove that the $m$-th fundamental form of such an $X$ at a general point has non empty base locus if and only if the points $p_i$ lie on a suitable degree-$m$ affine hypersurface. We then restrict to the case in which the points $p_i$ are all the lattice points of a lattice polytope and …
Toric real loci via moment polytopes
本文提出名为万花筒（kaleidoscope）的多面体模型，通过矩多面体组合学研究环面实轨迹拓扑，给出可定向性判据与欧拉示性数公式，统计复维数≤9的光滑环面法诺簇中实轨迹可定向的数量。
Laurent polynomial mirrors for quiver flag zero loci
本文针对高维法诺簇分类问题，将Gelfand–Cetlin退化推广到Y形箭图旗簇，提出构造法诺箭图旗零轨迹洛朗多项式镜像的方法，并验证了99个四维情形的猜想镜像。
Exceptional loci of F-blowups and $G$-Hilbert schemes
研究F吹胀正常分形变的例外极子，通过组合数据给出素除子中心维数公式，并探讨F吹胀与三维终端奇点和canonical奇点的关联。
Ample bodies and Terracini loci of projective varieties
本文引入射影簇的充足体概念，用以证明 Terracini 轨迹为空，并给出环面簇与齐次簇的特定可辨识性结论。
Real Toric Varieties: Interactions between their Geometry and their Topology
本文研究实环带簇的拓扑，特别关注环面不可分裂的情形，通过典型纤维化、贝蒂数计算、完全代数同调及可定向性判据的推广，并给出了三维不可分裂环面等变嵌入的拓扑分类。
In this article, we establish the arithmetic purity of strong approximation for smooth loci of weighted projective spaces. By using this result and the descent method, we also prove that the arithmetic purity of strong approximation with Brauer-Manin obstruction holds for any smooth and complete toric variety.
Boundedness of toric foliations
本文研究环面 Fano 叶状结构的有界性及相关轨迹连通性，并证明其插值 $δ$-lct 集合满足降链条件。
Adapting focal loci techniques used by Chiantini and Lopez, we provide lower bounds on the genera of curves contained in very general surfaces in Gorenstein toric threefolds. We illustrate the utility of these bounds by obtaining results on algebraic hyperbolicity of very general surfaces in toric threefolds.
Fixed point loci of moduli spaces of sheaves on toric varieties
该研究推广前人工作给出非奇异环面簇上纯等变层的组合描述，借助GIT构造对应模空间，显式表出Gieseker稳定层模空间的环面作用不动点轨迹，构造出对应Gieseker稳定性的等变线丛，并得到μ-稳定自反层模空间不动点轨迹的组合描述，可用于计算相关欧拉示性数生成函数。
In this paper, we study derived categories of certain toric varieties with Picard number three that are blowing-up another toric varieties along their torus invariant loci of codimension at most three. We construct strong full exceptional collections by using Orlov's blow-up formula and mutations.
There are matroid toric ideals without quadratic Gröbner bases
本文证明若拟阵包含Fano平面或其对偶作为子式，则其环面理想无二次Gröbner基，通过建立与正则单模旗三角剖分的联系并利用多面体重新表述解决Herzog和Hibi的著名问题。
Normal Bundle Splitting Strata of Rational Curves in Toric Varieties
本文研究环面簇中有理曲线法丛分裂型的分层，通过Cox构造和相对上同调态射给出非平衡性数值判据，并应用于射影空间爆破，与已有结果等价。
In this paper, we prove that: For any given finitely many distinct points $P_1,...,P_r$ and a closed subvariety $S$ of codimension $\geq 2$ in a complete toric variety over a uncountable (characteristic 0) algebraically closed field, there exists a rational curve $f:\mathbb{P}^1\to X$ passing through $P_1,...,P_r$, disjoint from $S\setminus \{P_1,...,P_r\}$ (see Main Theorem). As a corollary, we prove that the smooth loci of complete toric varieties are strongly rationally connected.
Toric Amplitudes and Universal Adjoints
本文研究了托利安幅度的代数性质及其与超曲面几何的关系，通过双体积解释揭示其与Warren伴随的联系。
We say that a group G acts infinitely transitively on a set X if for every integer m the induced diagonal action of G is transitive on the cartesian mth power of X with the diagonals removed. We describe three classes of affine algebraic varieties such that their automorphism groups act infinitely transitively on their smooth loci. The first class consists of affine cones over flag varieties, the second of non-degenerate affine toric varieties, and the third of iterated suspensions over affine varieties with infinitely transitive automorphism groups of a reinforced type.
Toric degenerations of weight varieties and applications
我们表明，一个重量品种，这是一个商的旗品种的极大环面，承认一个平坦的退化的复曲面品种。特别地，我们证明了空间多边形的模空间退化为极化复曲面簇，其矩多面体由其对角线的长度定义。我们将这些结果推广到更一般的关于射影空间乘积的行列式的Flaschka-Millson Hamilton算子。我们还研究边界复曲面因子和某些真正的轨迹。
In this note we introduce higher order polar loci as natural generalizations of the classical polar loci, replacing the role of tangent spaces by that of higher order osculating spaces. The close connection between polar loci and dual varieties carries over to a connection between higher order polar loci and higher order dual varieties. We generalize the duality between the degrees of polar classes of a variety and those of its dual variety to varieties that are reflexive to a higher order. In particular, the degree of the top (highest codimension) polar class of order k is equal to the degree…
Ehrhart polynomials and stringy Betti numbers
研究了Gorenstein复曲面簇的弦贝蒂数与某些多面体区域的Ehrhart多项式的母函数之间的关系。我们用这个观点给出了反例Hibi的猜想的单峰性的自反多面体的δ向量。
We describe a practical and effective method for reconstructing the deformation class of a Fano manifold X from a Laurent polynomial f that corresponds to X under Mirror Symmetry. We explore connections to nef partitions, the smoothing of singular toric varieties, and the construction of embeddings of one (possibly-singular) toric variety in another. In particular, we construct degenerations from Fano manifolds to singular toric varieties; in the toric complete intersection case, these degenerations were constructed previously by Doran--Harder. We use our method to find models of orbifold del …
Castelnuovo-Mumford regularity of toric varieties with at most one singular point
研究了至多一个奇点的简单投影托里克品种的拟正则性上界，结合组合与同调方法证明了Eisenbud-Goto界在光滑和单奇点情况下均成立。
Asymptotic invariants of base loci
本文定义并系统地研究了光滑射影簇上线丛的基轨迹的渐近不变量。我们区分一个开放的稠密子集的真正的大锥，称为稳定的轨迹，由一组类上的渐近基轨迹是局部常数。渐近不变量定义了大锥上的连续函数，粗略地说，其消失表征了不稳定轨迹。我们表明，至少对于复曲面品种，存在一个多面体分解的大锥上，这些功能是多项式。
On the Virtual Euler Characteristic of the Moduli Space of Stable Pairs on Surfaces
本文研究了环面上稳定对理论，确定了固定点轨迹上的虚拟切空间，提出计算虚拟欧拉示性数的程序并以射影平面为例说明，通过特例验证支持了有理性与对称性猜想。
We find a relation between mixed volumes of several polytopes and the convex hull of their union, deducing it from the following fact: the mixed volume of a collection of polytopes only depends on the product of their support functions (rather than on the individual support functions). For integer polytopes, this dependence is essentially a certain specialization of the isomorphism between two well-known combinatorial models for the cohomology of toric varieties, however, this construction has not been extended to arbitrary polytopes so far (partially due to the lack of combinatorial tools cap…
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