Nicolae Manolache
We construct lci nilpotent scheme structures $Y \subset P$ on a smooth variety $X$ embedded in a smooth variety $P$, which are, locally, (i.e. in $\widehat{\mathcal O}_{p,P}$ ) given by ideals of the form $(y^2+x^n, xy, z_1,...,z_r)$, $(y^3+x^n, xy, z_1 ,...z_r)$
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Motivated by a kind of Penrose correspondence, we investigate the space of hyperplane sections of Segre quartic surfaces which have an ordinary cusp. We show that the space of such hyperplane sections is empty for two kinds of Segre surfaces, and it is a connected surface for all other kinds of Segre surfaces. We also show that when it is non-empty, the closure of the space is either birational to the surface itself or birational to a double covering of the surface, whose branch divisor consists of some specific lines on the surface.
On cuspidal sections of algebraic fundamental groups
具有充分非平凡Kummer理论的域上的双曲曲线的边界上的有理点是基本群正合列的大量截面的来源。我们遵循和完善中村的方法对这些边界部分。例如，我们得到了一个弱的anabel定理双曲亏格0曲线在相当一般的领域，包括例如最大的阿贝尔扩张的有理数。
We study rational cuspidal curves in projective surfaces. We specify two criteria obstructing possible configurations of singular points that may occur on such curves. One criterion generalizes the result of Fernandez de Bobadilla, Luengo, Melle--Hernandez and Nemethi and is based on the Bezout theorem. The other one is a generalization of the result obtained by Livingston and the author and relies on Ozsvath--Szabo inequalities for $d$-invariants in Heegaard Floer homology. We show by means of explicit calculations that the two approaches give very similar obstructions.
In this paper we continue the work of using the recent advances in algebraic $K$-theory to extend computations done in characteristic $p$ to the mixed characteristic setting using perfectoid rings. We extend the work of Hesselholt-Nikolaus in \cite{Hesselholt_Nikolaus} on the algebraic $K$-Theory of cuspidal curves. We consider both cuspidal curves and the $p$-completion of cuspidal curves. Along the way we also study the $K$-theory of the $p$-completed affine line over a perfectoid ring.
Enumerative algebraic geometry deals with problems of counting geometric objects defined algebraically, An important class of enumerative problems is that of counting curves: given a class of curves in some projective variety defined by fixing some algebraic or geometric invariants (such as degree, genus and types of singularities), the problem usually takes the form of "how many curves of that class pass through a configuration of n points in general position?" Tropical Geometry deals with certain piecewise-linear complexes, which arise as degeneration of families of complex algebraic varieti…
Several results on presenting an affine algebraic group variety as a product of algebraic varieties are obtained.
In this paper we study certain homogeneous spaces, which we call generalised affine Stiefel algebraic varieties. The main aim is to characterise the canonical divisor of generalised affine Stiefel algebraic varieties in terms of group representations. Affine Stiefel algebraic varieties and in particular $S^{n}$ are two special cases of the generalised affine Stiefel algebraic varieties.
ICM lecture on minimal models and moduli of varieties.
We introduce an invariant of a finite point configuration $A \subset \mathbb{R}^{1+n}$ which we denote the cuspidal form of $A$. We use this invariant to extend Esterov's characterization of dual defective point configurations to exponential sums; the dual variety associated to $A$ has codimension at least $2$ if and only if $A$ does not contain any iterated circuit.
We study Minkowski sums and Hadamard products of algebraic varieties. Specifically we explore when these are varieties and examine their properties in terms of those of the original varieties.
We introduce a new construction of towers of algebraic curves over finite fields and provide a simple example of an optimal tower.
Syzygies of algebraic varieties through symmetric products of algebraic curves
本文综述了利用代数曲线对称积的几何方法证明的关于代数簇合冲的若干近期结果，包括亏格猜想、割线簇与切发展曲面的合冲、格林猜想及渐近合冲。
In this short article we provide a proof of the Iitaka conjecture for algebraic fiber spaces over abelian varieties.
We study projective varieties whose universal cover is biholomorphic to a semialgebraic open subset of a projective variety.
Exercises in the birational geometry of algebraic varieties
这是一个大约100个练习的集合。它可以作为一个补充书Kollár-森：双有理几何的代数簇。
Algebraic independence in the Grothendieck ring of varieties
给出了域$k$上簇的类在域$k$上簇的Grothendieck环中代数独立的充分上同调准则，并构造了一些例子.
We show that every affine or projective algebraic variety defined over the field of real or complex numbers is homeomorphic to a variety defined over the field of algebraic numbers. We construct such a homeomorphism by choosing a small deformation of the coefficients of the original equations. This method is based on the properties of Zariski equisingular families of varieties. Moreover we construct an algorithm, that, given a system of equations defining a variety $V$, produces a system of equations with algebraic coefficients of a variety homeomorphic to $V$
We construct smooth rational real algebraic varieties of every dimension $\ge$ 4 which admit infinitely many pairwise non-isomorphic real forms.
We develop a moduli theory of algebraic varieties and pairs of non-negative Kodaira dimension. We define stable minimal models and construct their projective coarse moduli spaces under certain natural conditions. This can be applied to a wide range of moduli problems in algebraic geometry.
On the density of rational and integral points on algebraic varieties
证明了Heath-Brown关于一类射影簇的有界高的有理点个数的一个猜想。
An approach to the abundance conjecture for Kähler varieties via algebraic reduction
本文通过归纳法建立Kähler变种丰富性猜想的策略，利用代数减少纤维化将问题转化为射影变种的丰富性猜想，特别在四维情况下获得了一些非代数或轨型为零的Kähler四重的丰富性猜想案例。
We address the question of finding algebraic properties that are respectively equivalent, for a morphism between algebraic varieties over an algebraically closed field of characteristic zero, to be an homeomorphism for the Zariski topology and for a strong topology that we introduce. Our answers involve a study of seminormalization and saturation for morphisms between algebraic varieties, together with an interpretation in terms of continuous rational functions on the closed points of an algebraic variety. The continuity refers to the strong topology which is the usual Euclidean topology in th…
In this paper, we establish the following version at infinity of Whitney's theorem [6, 7]: Geometric and algebraic tangent cones at infinity of complex algebraic varieties coincide. The proof of this fact is based on a geometric characterization of geometric tangent cones at infinity and using the global Łojasiewicz inequality with explicit exponents for complex algebraic varieties. We also show that tangent cones at infinity of complex algebraic varieties can be computed using Gröbner bases.
Relative Lipschitz saturation of complex algebraic varieties
本文研究复代数簇的相对Lipschitz饱和，解答了Pham和Teissier关于一般代数Lipschitz饱和有限性的公开问题，并给出两代数簇可被闭点上局部双Lipschitz同胚的代数态射连接的代数判据。
Real structures on complex algebraic varieties with a reductive group action
这是一篇数学代数几何领域的综述，聚焦于研究带有约化群作用的复代数簇上的实结构相关内容。
On vanishing of fundamental forms of algebraic varieties
本文利用线丛主部层研究代数簇基本形式，建立任意阶消没定理，并揭示其与高阶高斯映射和高阶切簇的联系。
Algebraicity of Hodge classes on some generalized Prym Varieties
本文通过重新审视Chad Schoen在特定Prym簇上构造的代数环，利用无分歧几何类域论证明某些广义Prym簇上Hodge类的代数性。
We extend the Altmann-Hausen presentation of normal affine algebraic C-varieties endowed with effective torus actions to the real setting. In particular, we focus on actions of quasi-split real tori, in which case we obtain a simpler presentation.
This is a report on some of the main developments in birational geometry in the last few years focusing on the minimal model program, Fano varieties, singularities and related topics, in characteristic zero.
On Algebraic Hyperbolicity of Log Varieties
在P^n中固定一个次数至少为2n + 1的非常一般的超曲面D，我们证明补P^n-D不包含任何代数环面C^*。
This article proposes a generalization of tautological rings introduced by Beauville and Moonen for Jacobians. The main result is that, under certain hypotheses, the special subvarieties of Prym varieties are algebraically equivalent and their classes belong to the tautological ring.
On the size of the fibers of a morphism of algebraic varieties
本文证明代数簇态射中纤维大小等于给定整数或无穷大的点集是可构造集。
We discuss relations between certain invariants of varieties in positive characteristic, like the a-number and the height of the Artin-Mazur formal group. We calculate the a-number for Fermat surfaces
We define an analog in characteristic $p>0$ of the proalgebraic completion of the topological fundamental group of a complex manifold.
We define the class of admissible linear embeddings of flag varieties. The definition is given in the general language of algebraic geometry. We then prove that an admissible linear embedding of flag varieties has a certain explicit form in terms of linear algebra. This result enables us to show that any direct limit of admissible embeddings of flag varieties is isomorphic to an ind-variety of generalized flags as defined in [DP]. These latter ind-varieties have been introduced in terms of the ind-group SL(\infty) (respectively, O(\infty) or Sp(\infty) for isotropic generalized flags), and the…
We show that the above\,-\,named property (after M.\,Larsen and V.\,Lunts) does not hold in general.
We give a short appreciation of Mumford's work on the moduli of varieties by putting it into historical context. By reviewing earlier works we highlight the innovations introduced by Mumford. Then we discuss recent developments whose origins can be traced back to Mumford's ideas.
We prove that a quasi-finite endomorphism of an algebraic variety over an algebraically closed field of characteristic zero, that is injective on the complement of a closed subvariety, is an automorphism. We also prove that an endomorphism of complex algebraic variety that is injective on the complement of a closed subvariety of codimension at least $2$, is an automorphism.
Virtual Betti numbers of real algebraic varieties
利用双有理映射的弱因子分解定理证明了：对所有非负i，紧致非奇异实代数簇的第i个mod 2贝蒂数对所有实代数簇的“虚贝蒂数“beta_i有唯一的扩张，使得若Y是X的闭子簇，则beta_i（X）= beta_i（X \Y）+ beta_i（Y）.
Geometry on arc spaces of algebraic varieties
弧空间是代数几何和奇点理论中的一个新课题。代数簇的弧空间的几何学产生了几个新的几何不变量，并给一些经典的不变量带来了新的启示。
Effective Whitney Stratification of Real Algebraic Varieties
本研究提出计算实代数簇惠特尼分层的新算法，采用余法线或极线技术处理实簇复化并证明其可用实多项式描述，还将方法拓展至全半代数集与实代数映射的分层问题。
Lee and Pandharipande studied a "double point" algebraic cobordism theory of varieties equipped with vector bundles, and speculated that some features of that story might extend to the case of varieties with principal G-bundles. This note shows that this expectation holds rationally, and more generally after inverting the torsion index of the group, for reductive G. We show that (after inverting the torsion index) the full theory for bundles on varieties is an extension of scalars of standard algebraic cobordism, that the theory for a point is dual to Omega^*(BG), and describe how the theory f…
Another introduction to perverse sheaves with some exercises. Expanded version of five lectures at the 2015 PCMI.
Connected components of real algebraic varieties invariant under the $CB_{n}$-Coxeter group are investigated. In particular, we consider their maximal number and their geometric and topological properties. This provides a decomposition for the space of $CB_{n}$-algebraic varieties. We construct $CB_{n}$-polynomials using Young-posets and partitions of integers. Our results establish bounds on the number of connected components for a given set of coefficients. It turns out that this number can achieve an upper bound of $2^{n}+1$ for specific coefficients. We introduce a new method to characteri…
Topological properties of real algebraic varieties: du côté de chez Rokhlin
综述了70年代初由V.I.Arnold和V.A.Rokhlin开创的实代数簇拓扑学的研究成果。我们试图系统化的主要结果在这个问题上。在一般工具和结果的阐述之后，特别注意曲面和曲面上的曲线。
Infinite-dimensional algebraic varieties and proof of the Jacobian Conjecture
由于命题2.13的证明中的一个错误，本文已被作者撤回。
We extend Kollar's technique to look for an explicit function h(n) with phi_m birational onto its image for all integers $m\geq h(n)$ and for all n-dimensional nonsingular projective varieties of general type.
In this paper we study a notion of volume for Cartier divisors on arbitrary blow-ups of normal complex algebraic varieties of dimension greater than one, with a distinguished point. We apply this to study a volume for normal isolated singularities, generalizing work on surfaces done by Wahl. We also compare this volume of isolated singularities to a different generalization due to Boucksom, de Fernex and Favre.
We associate to each real algebraic variety a filtered chain complex, the weight complex, which is well-defined up to filtered quasi-isomorphism, and which induces on classical (compactly supported) homology with Z/2 coefficients an analog of the weight filtration for complex algebraic varieties. This complements our previous definition of the weight filtration of Borel-Moore homology.
Let $k$ be a field of characteristic $p>0$ not necessarily perfect. Using Berthelot's theory of arithmetic $\mathcal{D}$-modules, we construct a $p$-adic formalism of Grothendieck's six operations for realizable $k$-schemes of finite type.
We extend Kolchin's results on linear dependence over projective varieties in the constants, to linear dependence over arbitrary complete differential varieties. We show that in this more general setting, the notion of linear dependence still has necessary and sufficient conditions given by the vanishing of a certain system of differential polynomials equations. We also discuss some conjectural questions around completeness and the catenary problem.
Algebraic hyperbolicity of very general hypersurfaces in homogeneous varieties
本文推广了Coskun、Riedl和Yeong的技巧，得到了有理齐次簇中非常一般超曲面的代数双曲性的几乎最优次数界，并给出了格拉斯曼簇、正交/辛格拉斯曼簇及旗簇等实例。
Flasque quasi-resolutions of algebraic varieties
本文将代数环面的Flasque消解概念推广到含齐性空间在内的更广泛代数簇，并据此得到齐性空间$R$-等价类数量的增强下界。
Estimates of Characteristic numbers of real algebraic varieties
给出了实次小于$d$的实代数流形的配边类个数的显式界，以及复次小于$d$的复流形的实型的$\mod 2$贝蒂数之和的大小的显式界.
We seek to determine a real algebraic variety from a fixed finite subset of points. Existing methods are studied and new methods are developed. Our focus lies on aspects of topology and algebraic geometry, such as dimension and defining polynomials. All algorithms are tested on a range of datasets and made available in a Julia package.
We show that every connected commutative algebraic group over an algebraically closed field of characteristic 0 is the Picard variety of some projective variety, obtained by pinching a smooth variety along a finite subscheme. In contrast, no Witt group of dimension at least 3 over a perfect field of prime characteristic is isogenous to the Picard variety obtained by this construction.
Divisorial contractions of algebraic varieties
这篇论文已被作者撤回。环面奇点的plt爆破不是环面的（在3维也是），第一个主要定理也是不正确的。错误在于变形参数。我感谢伊万·切尔佐夫的讨论。
For a smooth manifold $X$ equipped with a volume form, let $\dL$ be the Lie algebra of volume preserving smooth vector fields on $X$. A. Lichnerowicz proved that the abelianization of $\dL$ is a finite-dimensional vector space, and that its dimension depends only on the topology of $X$. In this paper we provide analogous results for some classical examples of non-singular complex affine algebraic varieties that admit a nowhere-zero algebraic form of top degree (which plays the role of a volume form).
This note is about cycle-theoretic properties of the Fano variety of lines on a smooth cubic fivefold. The arguments are based on the fact that this Fano variety has finite-dimensional motive. We also present some results concerning Chow groups of Fano varieties of lines on certain cubics in other dimensions.
We present a modern proof of a theorem of Rosenlicht, asserting that every variety as in the title is isomorphic to a product of affine lines and punctured affine lines.
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