Delta invariants of projective bundles and projective cones of Fano type
Kewei Zhang, Chuyu Zhou
本文针对Fano型射影丛与射影锥，建立了计算其Delta不变量的精确公式，为相关几何量的确定提供了明确工具。
本文给出了计算Fano型射影丛和射影锥的Delta不变量的精确公式。
In this paper, we will give a precise formula to compute delta invariants of projective bundles and projective cones of Fano type.
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K-semistability of log Fano cone singularities
本文给出了log Fano锥奇点K-半稳定性的非阿基米德刻画，证明其与Collins--Székelyhidi的原始定义一致，并揭示了测试K-半稳定性只需测试特殊测试配置及其与lc位置的联系。
Mori cone is rigid in smooth connected families of Fano manifolds.
We prove two new results on the K-polystability of Q-Fano varieties based on purely algebro-geometric arguments. The first one says that any K-semistable log Fano cone has a special degeneration to a uniquely determined K-polystable log Fano cone. As a corollary, we combine it with the differential-geometric results to complete the proof of Donaldson-Sun's Conjecture which says that the metric tangent cone of any close point appearing on a Gromov-Hausdorff limit of Kahler-Einstein Fano manifolds only depends on the algebraic structure of the singularity. The second result says that for any lo…
In this note, we will show that delta invariant of a log Fano pair can be approximated by lc places of complements of plt type if it is no greater than one. Give a log Fano pair with delta invariant no greater than one, under the assumption that delta invariant of the log Fano pair can be approximated by lc places of bounded complements of plt type, we show the existence of the divisorial valuation computing delta invariant of this log Fano pair.
For a variety $X$, a big $\mathbb{Q}$-divisor $L$ and a closed connected subgroup $G \subset \mathrm{Aut}(X, L)$ we define a $G$-invariant version of the $δ$-threshold. We prove that for a Fano variety $(X, -K_X)$ and a connected subgroup $G \subset \mathrm{Aut}(X)$ this invariant characterizes $G$-equivariant uniform $K$-stability. We also use this invariant to investigate $G$-equivariant $K$-stability of some Fano varieties with large groups of symmetries, including spherical Fano varieties. We also consider the case of $G$ being a finite group.
The Morrison--Kawamata Cone Conjecture predicts that the action of the automorphism group on the effective nef cone and the action of the pseudo-automorphism group on the effective movable cone of a klt Calabi-Yau pair have rational, polyhedral fundamental domains. In a previous paper, we proved the conjecture for certain blowups of Fano manifolds of index n-1. In this paper, we consider the Morrison--Kawamata conjecture for blowups of Fano manifolds of index n-2.
On Casagrande-Druel Fano varieties with Lefschetz defect 2
本文研究Lefschetz缺陷为2的Casagrande-Druel Fano簇，证明19族Fano三维簇中15族源于构造A，并构造147族Fano四维簇，完成分类，同时推广至构造B覆盖18族。
The affine cones over Fano-Mukai fourfold of genus $7$ are flexible
本文证明了亏格 $7$ 的任何光滑 Fano-Mukai 四重折叠的仿射锥具有柔性。
This is the first of a series of three papers which provide proofs of results announced recently in arXiv:1210.7494.
Variation of cones of divisors in a family of varieties -- Fano type case
研究纤维上Fano类型性质与整体Fano类型性质的关系，证明在一般有限基变换后，Fano类型簇族的Néron-Severi空间、nef锥、有效锥、可动锥和Mori chamber分解的不变性，并应用于有界性问题。
We address the following question: When an affine cone over a smooth Fano threefold admits an effective action of the additive group? In this paper we deal with Fano threefolds of index 1 and Picard number 1. Our approach is based on a geometric criterion from our previous paper, which relates the existence of an additive group action on the cone over a smooth projective variety X with the existence of an open polar cylinder in X. Non-trivial families of Fano threefolds carrying a cylinder were found in loc. cit. Here we provide new such examples.
We classify the cones of curves of Fano varieties of dimension greater or equal than five and (pseudo)index dim X -3, describing the number and type of their extremal rays.
In this short note we show that the closed cone of moving curves of a smooth Fano-threefold is polyhedral. The proof relies on a famous result of Bucksom, Demailly, Paun and Peternell which says that the strongly movable cone is dual to the cone of pseudoeffective divisors. Finally, we relate the extremal rays of the cone of moving curves on a threefold with extremal rays in the cone of strongly movable curves on a birational model obtained by a Mori contraction.
We show that the affine cones over any Fano-Mukai fourfold of genus 10 are flexible; in particular, the automorphism group of such a cone acts highly transitively outside the vertex. Furthermore, any Fano-Mukai fourfold of genus 10, with one exception, admits a covering by open charts isomorphic to the affine four-space.
We describe the closed cone of moving curves of smooth Fano three- and fourfolds by giving finitely many equations that cut out the cone. The equations are induced by the exceptional divisors of divisorial contractions and by nef divisors on birational models obtained by sequences of flips.The results presented here are part of the author's Ph.D. thesis, written under the supervision of Stefan Kebekus.
Boundedness of log Fano cone singularities and discreteness of local volumes
本文证明固定维度下体积有下界的K-半稳定log Fano锥奇点有界，进而得出klt奇点局部体积集合仅以零为聚点。
Delta invariants of weighted hypersurfaces
本文通过Abban-Zhuang方法和加权超曲面线性系研究，证明了大量准光滑Fano超曲面的K稳定性。
This is the third and final paper in a series which establish results announced in arXiv:1210.7494. In this paper we consider the Gromov-Hausdorff limits of metrics with cone singularities in the case when the limiting cone angle approaches 2π. We also put all our technical results together to complete the proof of the main theorem that if a K-stable Fano manifold admits a Kahler-Einstein metric.
The Morrison-Kawamata cone conjecture predicts that the actions of the automorphism group on the effective nef cone and the pseudo-automorphism group on the effective movable cone of a klt Calabi-Yau pair $(X, Δ)$ have finite, rational polyhedral fundamental domains. Let $Z$ be an $n$-dimensional Fano manifold of index $n-1$ such that $-K_Z = (n-1) H$ for an ample divisor $H$. Let $Γ$ be the base locus of a general $(n-1)$-dimensional linear system $V \subset |H|$. In this paper, we verify the Morrison-Kawamata cone conjecture for the blow-up of $Z$ along $Γ$.
We compute the cones of effective divisors on blowups of $\mathbb{P}^1 \times \mathbb{P}^2$ and $\mathbb{P}^1 \times \mathbb{P}^3$ in up to 6 points. We also show that all these varieties are log Fano, giving a conceptual explanation for the fact that all the cones we compute are rational polyhedral.
The Miyaoka-Yau inequality and the delta invariant for Fano varieties I -klt Fano case-
研究针对\(n\)维klt法诺簇建立宫冈 - 丘不等式，还受他人启发在孤子情形下证明其等变形式，用等变陈类和加权δ不变量取代相关量，得出允许凯勒 - 里奇孤子的光滑法诺流形的等变宫冈 - 丘不等式。
This is the second of a series of three papers which provide proofs of results announced in arXiv:1210.7494. In this paper we consider the Gromov-Hausdorff limits of metrics with cone singularities in the case when the limiting cone angle is less than 2π. We show that these are in a natrual way projective algebraic varieties. In the case when the limiting variety and the limiting divisor are smooth we show that the limiting metric also has standard cone singularities.
K-stablity of Fano threefold hypersurfaces of index 1
通过给出delta不变量的下界，解决了Fano指数为1的拟光滑Fano三维超曲面的K-稳定性问题，使用了Abban和Zhuang引入的方法计算Fano三维超曲面旗上的delta不变量下界。
We construct Q-factorial terminal Fano varieties, starting in dimension 4, whose nef cone jumps when the variety is deformed. It follows that de Fernex and Hacon's results on deformations of 3-dimensional Fanos are optimal. The examples are based on the existence of high-dimensional flips which deform to isomorphisms, generalizing the Mukai flop. We also extend de Fernex and Hacon's positive results on deformations of Fano varieties. Toric Fano varieties which are smooth in codimension 2 and Q-factorial in codimension 3 are rigid. The divisor class group is deformation-invariant for klt Fanos …
On the existence of minimizer on a log Fano cone singularity
针对不可数代数闭域上的对数法诺锥奇点，证明了满足条件的𝕋-不变赋值对应的比值δ存在极小值，采用通用极限论证，舍弃对数法诺锥结构则存在反例。
Let X be a smooth, complex Fano variety, and delta(X) its Lefschetz defect. It is known that if delta(X) is at least 4, then X is isomorphic to a product SxT, where dim T=dim X-2. In this paper we prove a structure theorem for the case where delta(X)=3. We show that there exists a smooth Fano variety T with dim T=dim X-2 such that X is obtained from T with two possible explicit constructions; in both cases there is a P^2-bundle Z over T such that X is the blow-up of Z along three pairwise disjoint smooth, irreducible, codimension 2 subvarieties. Then we apply the structure theorem to Fano 4-fo…
K-polystability and reduced uniform K-stability of log Fano cone singularities
研究证明log Fano锥奇点在特定条件下K-多项稳定性与特殊测试配置的K-多项稳定性等价，并建立其减少均匀K稳定性等价于K-多项稳定性。
The movable cone of Calabi--Yau threefolds in ruled Fano manifolds
本文显式描述了直纹 Fano 流形中一般完全交 Calabi-Yau 三维流形的可动锥 chamber 结构，并找到了其所有有限个双有理极小平凡模型。
We study the cones of q-ample divisors on smooth complex varieties. In favourable cases, we identify a part where the closure of this cone and the nef cone have the same boundary. This is especially interesting for Fano (or almost Fano) varieties.
On the cone conjecture for log Calabi-Yau mirrors of Fano 3-folds
该研究针对带K3纤维化的光滑射影3-fold，证明当三阶上同调群为零时伪自同构群在可动锥余维一面上的轨道有限，验证了锥猜想的特例，且该类3-fold可作为Fano 3-folds的对数Calabi-Yau镜像。
Betti numbers and pseudoeffective cones in 2-Fano varieties
本文提出（弱）k-Fano 簇的定义并猜想其伪有效 k-闭链锥具有多面体性，通过计算一大类 k-Fano 簇的 Betti 数证明了该猜想在指数≥n-2 的 2-Fano 簇等特殊情形下成立，并完成弱 2-Fano 簇的分类。
On the Futaki invariant of Fano threefolds
本文研究K-多稳态Fano三维流形上Futaki不变量的零点集，证明除Iskovskikh-Mori-Mukai分类中的八个族外该不变量在Kähler锥上恒为零，并构造二维Kähler类族，进而推出非Kähler-Einstein的cscK度量的存在性。
We show that uniform K-stability is a Zariski open condition in Q-Gorenstein families of Q-Fano varieties. To prove this result, we consider the behavior of the stability threshold in families. The stability threshold (also known as the delta-invariant) is a recently introduced invariant that is known to detect the K-semistability and uniform K-stability of a Q-Fano variety. We show that the stability threshold is lower semicontinuous in families and provide an interpretation of the invariant in terms of the K-stability of log pairs.
We show that delta invariant is a continuous function on the big cone. We will also introduce an analytic delta invariant and show its continuity in the Kähler cone, from which we deduce the continuity of the greatest Ricci lower bound. Then building on the work Berman-Boucksom-Jonsson, we obtain a uniform Yau-Tian-Donaldson theorem for twisted Kähler-Einstein metrics in general Kähler classes.
In this work we deal with vector bundles of rank two on a Fano manifold $X$ with $b_2=b_4=1$. We study the nef and pseudoeffective cones of the corresponding projectivizations and how these cones are related to the decomposability of the vector bundle. As consequences, we obtain the complete list of $\mathbb{P}^1$-bundles over $X$ that have a second $\mathbb{P}^1$-bundle structure, classify all the uniform rank two vector bundles on this class of Fano manifolds and show the stability of indecomposable Fano bundles (with one exception on $\mathbb{P}^2$).
A conjecture of Batyrev and Manin relates arithmetic properties of varieties with ample anticanonical class to geometric invariants; in particular, counting functions defined by metrized ample line bundles and the corresponding asymptotics of rational points of bounded height are interpreted in terms of cones of effective divisors and certain thresholds with respect to these cones. This framework leads to the notion of balanced line bundles, whose counting functions, conjecturally, capture generic distributions of rational points. We investigate balanced line bundles in the context of the Mini…
On the geometry of Fano varieties with Lefschetz defect 2
本文研究莱夫谢茨缺陷为2的光滑复法诺簇的几何，通过翻转序列得到其圆锥丛结构，分析圆锥丛的光滑性或德·佩佐纤维化性质，最终构造出表现该行为的法诺四维簇族。
The fundamental property of Fano varieties with mild singularities is that they have a finite polyhedral Mori cone. Thus, it is very interesting to ask: What we can say about algebraic varieties with a finite polyhedral Mori cone? I give a review of known results. All of them were obtained applying methods which were originated in the theory of discrete groups generated by reflections in hyperbolic spaces with a fundamental chamber of finite volume. This is my report on Fano conference in Torino, October 2002
Let $D$ be a Fano manifold that may be realised as $\mathbb{P}(\mathcal{E})$ for some rank $2$ holomorphic vector bundle $\mathcal{E}\longrightarrow Z$ over some Fano manifold $Z$. Let $k\in\mathbb{N}$ divide $c_{1}(D)$. We classify those Kähler cones of dimension $\leq4$ of the form $(\frac{1}{k}K_{D})^{\times}$ that are smoothable. As a consequence, we find that any irregular Calabi-Yau cone of dimension $\leq 4$ of this form does not admit a smoothing, leaving $K_{\mathbb{P}^{2}_{(2)}}^{\times}$ as currently the only known example of a smoothable irregular Calabi-Yau cone in these dimension…
A Bott tower of height $r$ is a sequence of projective bundles $$X_r \overset{π_r}\longrightarrow X_{r-1} \overset{π_{r-1}}\longrightarrow \cdots \overset{π_2}\longrightarrow X_1=\mathbb P^1 \overset{π_1} \longrightarrow X_0=\{pt\}, $$ where $X_i=\mathbb P (\mathcal O_{X_{i-1}}\oplus \mathcal L_{i-1})$ for a line bundle $\mathcal L_{i-1}$ over $X_{i-1}$ for all $1\leq i\leq r$ and $\mathbb P(-)$ denotes the projectivization. These are smooth projective toric varieties and we refer to the top object $X_{r}$ also as a Bott tower. In this article, we study the Mori cone and numerically effective …
From Kähler Ricci solitons to Calabi-Yau Kähler cones
研究带有Kähler Ricci soliton的光滑Fano流形，通过动量多面体上的权函数方法，证明其与高维复射影空间乘积的规范锥是Calabi-Yau锥，并探讨了相关分支应用。
Valuative invariants for linearized line bundles on a spherical variety
该研究给出射影球簇上线性化充足线丛的赋值不变量公式，将其用于研究法诺球簇的g-孤立子，并证明法诺球极流形对应锥总存在Calabi-Yau锥度量。
We consider the problem to determine which blow-ups along subvarieties in products of two projective spaces are log Fano. By describing the nef cones of such blow-ups with special centers, we give a partial classification result. For each example, explicit boundary divisors are also given.
Let $U\subset \mathbb P^N$ be a projective variety which is not a cone and whose hyperplane sections are smooth Enriques surfaces. We prove that the degree of a $U$ is at most 32 and the bound is sharp.
We consider weak Fano manifolds with small contractions obtained by blowing up successively curves and subvarieties of codimension 2 in products of projective spaces. We give a classification result for a special case. In the process of proof, we describe explicitly the structure of nef cones and compute the self intersection numbers of anti-canonical divisors for such weak Fano manifolds.
Product theorem on delta invariants via adding a general boundary
本文利用添加一般边界产生 K-稳定性的已知结论，重新证明了 Fano 簇的 delta 不变量乘积定理。
In this paper we describe the geometry of the 2m-dimensional Fano manifold G parametrizing (m-1)-planes in a smooth complete intersection Z of two quadric hypersurfaces in the complex projective space P^{2m+2}, for m>0. We show that there are exactly 2^{2m+2} distinct isomorphisms in codimension one between G and the blow-up of P^{2m} at 2m+3 general points, parametrized by the 2^{2m+2} distinct m-planes contained in Z, and describe these rational maps explicitly. We also describe the cones of nef, movable and effective divisors of G, as well as their dual cones of curves. Finally, we determin…
In this paper we classify rank two Fano bundles $\cE$ on Fano manifolds satisfying $H^2(X,\Z)\cong H^4(X,\Z)\cong\Z$. The classification is obtained via the computation of the nef and pseudoeffective cones of the projectivization ${\mathbb{P}}(\cE)$, that allows us to obtain the cohomological invariants of $X$ and $\cE$. As a by-product we discuss Fano bundles associated to congruences of lines, showing that their varieties of minimal rational tangents may have several linear components.
Compact moduli of Calabi-Yau cones and Sasaki-Einstein spaces
本文通过局部归一化体积和高阶Θ-稳定约化，构造了K-多项式稳定ℚ-Fano锥（即Calabi-Yau锥）及其Sasaki-Einstein链环的紧致模代数空间，并给出了ℚ-Fano簇紧致K-模的不依赖δ-不变量与Donaldson-Futaki不变量的新代数构造。
We show that the affine cones over a general Fano-Mukai fourfold of genus $g=7$, $8$ and $9$ are flexible. Equivalently, there is an infinitely transitive action of the special automorphism group on such affine cones. In particular, any Mukai fourfold of genus $7,8$ and $9$ is $\Bbb A^2$-cylindrical.
Local delta invariants of weak del Pezzo surfaces with the anti-canonical degree $\geq 5$
本文基于delta不变量对K-稳定性的判别准则，确定了反典范度 $\geq 5$ 的所有弱 del Pezzo 曲面的整个局部 delta 不变量。
We show that Gorenstein singularities that are cones over singular Fano varieties provided by so-called flag quivers are smoothable in codimension three. Moreover, we give a precise characterization about the smoothability in codimension three of the Fano variety itself.
It is pretty well-known that toric Fano varieties of dimension k with terminal singularities correspond to convex lattice polytopes P in R^k of positive finite volume, such that intersection of P and Z^k consists of the point 0 and vertices of P. Likewise, Q-factorial terminal toric singularities essentially correspond to lattice simplexes with no lattice points inside or on the boundary (except the vertices). There have been a lot work, especially in the last 20 years or so on classification of these objects. The main goal of this paper is to bring together these and related results, that are…
On boundedness of singularities and minimal log discrepancies of Kollár components, II
本文证明K-半稳定log Fano锥奇点的有界性由局部体积下界和Kollár分量极小对数差异上界决定，并据此确认了三维情形的有界性猜想及klt奇点局部体积的聚集性质。
We prove that if a smooth variety with non-positive canonical class can be embedded into a weighted projective space of dimension $n$ as a well formed complete intersection and it is not an intersection with a linear cone therein, then the weights of the weighted projective space do not exceed $n+1$. Based on this bound we classify all smooth Fano complete intersections of dimensions $4$ and $5$, and compute their invariants.
Key variety construction of Sarkisov links for prime $\mathbb{Q}$-Fano threefolds of codimension four associated to Type ${\rm II}_{2}$ projections
本文基于II型投射相关四维素数Q-芬安三维流形，通过构造Sarkisov链接，展示了其以除子提取结束的纤维或收缩类型。
K-stability of Gorenstein Fano group compactifications with rank two
本文分类了秩二半单复李群的 Gorenstein Fano 双等变紧化，判定其等变 K-稳定性与 Kähler-Einstein 度量的存在性，并给出 K-不稳定情形下 delta 不变量及 II 型 Kähler-Ricci 流的新例子。
We compute the facets of the effective cones of divisors on the blow-up of P^3 in up to five lines in general position. We prove that up to six lines these threefolds are weak Fano and hence Mori Dream Spaces.
Quiver flag zero loci are subvarieties of quiver flag varieties cut out by sections of homogeneous vector bundles. We prove the Abelian/non-Abelian Correspondence in this context: this allows us to compute genus zero Gromov--Witten invariants of quiver flag zero loci. We determine the ample cone of a quiver flag variety, disproving a conjecture of Craw. In the Appendices, which are joint work with Tom Coates and Alexander Kasprzyk, we use these results to find four-dimensional Fano manifolds that occur as quiver flag zero loci in ambient spaces of dimension up to 8, and compute their quantum p…
We study the scalar curvature of Kähler metrics that have cone singularities along a divisor, with a particular focus on certain specific classes of such metrics that enjoy some curvature estimates. Our main result is that, on the projective completion of a pluricanonical bundle over a product of Kähler--Einstein Fano manifolds with the second Betti number 1, momentum-constructed constant scalar curvature Kähler metrics with cone singularities along the $\infty$-section exist if and only if the log Futaki invariant vanishes on the fibrewise $\mathbb{C}^*$-action, giving a supporting evidence t…
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