A note on octic hypersurfaces with many nodes

A note on rational curves on general Fano hypersurfaces

We show the Kontsevich space of rational curves of degree at most roughly $\frac{2-\sqrt{2}}{2}n$ on a general hypersurface $X\subset \mathbb{P}^n$ of degree $n-1$ is equidimensional of expected dimension and has two components: one consisting generically of smooth, embedded rational curves and the other consisting of multiple covers of a line. This proves more cases of a conjecture of Coskun, Harris, and Starr and shows the Gromov-Witten invariants in these cases are enumerative.

Les hypersurfaces cubiques sont séparablement rationnellement connexes

This note (which makes no claim to novelty) presents a proof of the separable rational connectedness of smooth cubic hypersurfaces, in any characteristic, by showing how to explicitly construct very free curves (of degree 3) on them. ----- Cette note (qui ne prétend pas à l'originalité) démontre la séparable rationnelle connexité des hypersurfaces cubiques lisses, en toute caractéristique, en construisant explicitement des courbes très libres (de degré 3) tracées dessus.

A note on resolution of rational and hypersurface singularities

It is well known that the exceptional set in a resolution of a rational surface singularity is a tree of rational curves. We generalize the combinatoric part of this statement to higher dimensions and show that the highest cohomologies of the dual complex associated to a resolution of an isolated rational singularity vanish. We also prove that the dual complex associated to a resolution of an isolated hypersurface singularity is simply connected. As a consequence, we show that the dual complex associated to a resolution of a 3-dimensional Gorenstein terminal singularity has the homotopy type o…

Six generated ACM bundles on a hypersurface

Let X be a smooth projective hypersurface. In this note we show that any six generated arithmetically Cohen-Macaulay vector bundle over X splits if dim X >= 6.

The standard conjectures for the variety of lines on a cubic hypersurface

The purpose of this note is to prove Grothendieck's standard conjectures for the Fano variety of lines on a smooth cubic hypersurface in projective space.

Erratum to: Birationally rigid hypersurfaces

This note points out a gap in the proof of the main theorem of the article "Birationally rigid hypersurfaces" published in Invent. Math. 192 (2013), 533-566, and provides a new proof of the theorem.

关于双次数 $(m, n)$ 超曲面的判别轨迹的注记

Note sur le lieu discriminant d'une hypersurface de bi-degré $(m, n).$

本文提出一种基于群胚描述单值性的新拓扑方法，用于研究射影空间乘积中代数簇的判别轨迹，并以双次数 $(m, n)$ 超曲面为例进行说明。

一般超曲面上的低度子簇

Subvarieties of low degree on general hypersurfaces

本文证明了大度数一般超曲面内的小度数子簇均由其与线性空间或其他簇相交生成。

Splitting of low rank ACM bundles on hypersurfaces of high dimension

Let $X$ be a smooth projective hypersurface. In this note we show that any rank 3 arithmetically Cohen-Macaulay vector bundle over $X$ splits when dim $X \geq 7$. We also find a splitting criterion for rank 4 arithmetically Cohen-Macaulay vector bundles on $X$ when dim $X \geq 9$.

关于奇异射影超曲面半稳定性的一个注记

A note on the semistability of singular projective hypersurfaces

本文利用次数、奇点最大重数与奇异轨迹维数，并结合 Benoist 的交维数下界及 Hilbert–Mumford 判据，给出奇异射影超曲面半稳定的充分条件。

On two upper bounds for hypersurfaces involving a Thas' invariant

Let $X^n$ be a hypersurface in $\mathbb{P}^{n+1}$ with $n\geq 1$ defined over a finite field $\mathbb{F}_q$ of $q$ elements. In this note, we classify, up to projective equivalence, hypersurfaces $X^n$ as above which reach two elementary upper bounds for the number of $\mathbb{F}_q$-points on $X^n$ which involve a Thas' invariant.

Harbourne constants and arrangements of lines on smooth hypersurfaces in $\mathbb{P}^3_{\mathbb{C}}$

In this note we find a bound for the so-called global linear Harbourne constants for smooth hypersurfaces in $\mathbb{P}^{3}_{\mathbb{C}}$

A note on the stable equivalence problem

We provide counterexamples to the stable equivalence problem in every dimension $d\geq2$. That means that we construct hypersurfaces $H_1, H_2\subset\mathbb{C}^{d+1}$ whose cylinders $H_1\times\mathbb{C}$ and $H_2\times\mathbb{C}$ are equivalent hypersurfaces in $\mathbb{C}^{d+2}$, although $H_1$ and $H_2$ themselves are not equivalent by an automorphism of $\mathbb{C}^{d+1}$. We also give, for every $d\geq2$, examples of two non-isomorphic algebraic varieties of dimension $d$ which are biholomorphic.

关于判别式为14的特殊三次四折与次数为10的非极小K3曲面的注记

A note on special cubic fourfolds of discriminant 14 and non-minimal K3 surfaces of degree 10

本文研究判别式14的特殊三次四折Hassett除子中的一般三次四折，证明其包含特定的10次非极小K3曲面，明确了该曲面的线构成与二次超曲面包含关系。

Hypersurfaces achieving the Homma-Kim bound

Let $X$ be a hypersurface in $\mathbb{P}^N$ with $N\geq 3$ defined over a finite field. The main result of this note is the classification, up to projective equivalence, of hypersurfaces $X$ as above without a linear component when the number of their rational points achieves the Homma-Kim bound.

Fano超曲面中的自由曲线必须具有高次数

Free curves in Fano hypersurfaces must have high degree

本文证明在正特征域中，Fano超曲面中自由有理曲线的最小次数无法由n的线性函数界定，并给出了超线性的界。

Rational curves on Fermat hypersurfaces

In this note we study rational curves on degree $p^r+1$ Fermat hypersurface in $\PP^{p^r+1}_k$, where $k$ is an algebraically closed field of characteristic $p$. The key point is that the presence of Frobenius morphism makes the behavior of rational curves to be very different from that of charateristic 0. We show that if there exists $N_0$ such that for all $e\geq N_0$ there is a degree $e$ very free rational curve on $X$, then $N_0> p^r(p^r-1)$.

On the Chow ring of certain hypersurfaces in a Grassmannian

This small note is about Plücker hyperplane sections $X$ of the Grassmannian $\operatorname{Gr}(3,V_{10})$. Inspired by the analogy with cubic fourfolds, we prove that the only non-trivial Chow group of $X$ is generated by Grassmannians of type $\operatorname{Gr}(3,W_{6})$ contained in $X$. We also prove that a certain subring of the Chow ring of $X$ (containing all intersections of positive-codimensional subvarieties) injects into cohomology.

A Note on $h^{2,1}$ of Divisors of CY Fourfolds I

In this note, we prove combinatorial formulas for $h^{2,1}$ of prime toric divisors in an arbitrary toric hypersurface Calabi-Yau fourfold $Y_4.$ We show that it is possible to find a toric hypersurface Calabi-Yau in which there are more than $h^{1,1}(Y_4)$ non-perturbative superpotential terms with trivial intermediate Jacobian. Hodge numbers of divisors in toric CICYs are the subjects of the part two.

On irrationality of hypersurfaces In $\mathbf{P}^{n+1}$

In this note, we study various measures of irrationality for hypersurfaces in projective spaces which were recently proposed by Bastianelli, De Poi, Ein, Lazarsfeld and Ullery. In particular, we answer the question raised by Bastianelli that if $X \subset P^{n+1}$ is a very general smooth hypersurface of dimension $n$ and degree $d\geq 2n+2$, then $\text{stab.irr}(X)=\text{uni.irr}(X)=d-1$. As a corollary, we prove that $\text{irr}(X\times P^{m})=\text{irr}(X)$ for any integer $m\geq 1$.

Espace des modules des faisceaux semi-stables de rang 2 et de classes de Chern $c_{1}=0$, $c_{2}=2$ et $c_{3}=0$ sur une hypersurface cubique lisse de $\mathbb{P}^{4}$

In this note we study the moduli space of rank two semistable sheaves on a smooth cubic hypersurface $X\subset\mathbb{P}^{4}$ with $c_{1}=0$, $c_{2}=2$ and $c_{3}=0$. We show that it is isomorphic to the blow-up of the intermediate jacobian $J(X)$ of $X$ along the Fano surface of $X$. We complete previous results of Iliev-Markushevich AG/9910058 and Markushevich-Tikhomirov AG/9910063.

超曲面的高阶Du Bois奇点与高阶有理奇点

Higher Du Bois and higher rational singularities of hypersurfaces

本研究针对全局定义的超曲面，利用消失循环混合霍奇模的Hodge滤过给出高阶Du Bois与高阶有理奇点的等价刻画，并提出基于谱Hirzebruch-Milnor特征类的同调检测准则。

A note on the maximal rank

We give an upper-bound for the $X$-rank of points with respect to a non-degenerate irreducible variety $X$ in the case that sub-generic $X$-rank points generate a hypersurface. We give examples where this bound is sharp and it improves the existing ones.

关于微分同胚意义下复平面曲线奇点及其刚性的注记

A note on complex plane curve singularities up to diffeomorphism and their rigidity

本文证明了在实光滑微分同胚下等价的平面曲线奇点必然复同构或共轭复同构，给出了基于泰勒级数的构造性证明，并将结论推广至非不可约超曲面情形。

关于孤立复超曲面奇点的一个注记

A remark on isolated complex hypersurface singularities

本文研究了复超曲面奇点的解析等价性问题，提出D(n,m)=n(m-2)+1的公式，并扩展到准齐次多项式情况。

F-pure thresholds of binomial hypersurfaces

In this note, we use estimates given in the recent preprint [Her11b]to deduce a formula for the F-pure threshold of a binomial hypersurface over a field of prime characteristic. These formulas are given in terms of the associated splitting polytope, and remain valid over any characteristic.

Hyperbolic hypersurfaces in P^n of Fermat-Waring type

In this note we show that there are algebraic families of hyperbolic, Fermat-Waring type hypersurfaces in P^n of degree 4(n-1)^2, for all dimensions n>1. Moreover, there are hyperbolic Fermat-Waring hypersurfaces in P^n of degree 4n^2-2n+1 possessing complete hyperbolic, hyperbolically embedded complements.

Looking for rational curves on cubic hypersurfaces

These are the substantially expanded notes of the lectures of JK at the summer school "Higher-Dimensional Geometry over Finite Fields" in Göttingen, June 2007. The first part gives an overview of the methods. The main new result is the construction of rational curves passing through a given collection of points on smooth cubic hypersurfaces over finite fields.

Algebraic cycles on hyperplane sections of hypersurfaces in $\mathbb P^n$ for $n=5,6$

Let $X$ be a cubic hypersurface in $\mathbb P^6$ or a hypersurface of degree greater than equal to $7$ in $\mathbb P^5$. In this note we try to understand, for a very general hyperplane section of $X$, the non-injectivity locus of the corresponding push-forward homomorphism at the level of Chow group of certain dimension.

关于孤立超曲面奇点：代数几何与辛几何方面

On isolated hypersurface singularities: algebra-geometric and symplectic aspects

本文基于2022年莱顿大学研讨会，旨在阐释Evans和Lekili关于孤立奇点Milnor纤维辛上同调的工作，通过介绍代数几何与辛几何的核心思想使其更易理解。

A survey on hyperbolicity of projective hypersurfaces

These are lecture notes of a course held at IMPA, Rio de Janiero, in september 2010: the purpose was to present recent results on Kobayashi hyperbolicity in complex geometry. Our ultimate goal is to describe the results obtained on questions related to the geometry of entire curves traced in generic complex projective hypersurfaces of high degree. For the convenience of the reader, this survey tries to be as self contained as possible.

On the number of intersection points of the contour of an amoeba with a line

In this note, we investigate the maximal number of intersection points of a line with the contour of hypersurface amoebas in $\mathbb{R}^n$. We define the latter number to be the $\mathbb{R}$-degree of the contour. We also investigate the $\mathbb{R}$-degree of related sets such as the boundary of amoebas and the amoeba of the real part of hypersurfaces defined over $\mathbb{R}$. For all these objects, we provide bounds for the respective $\mathbb{R}$-degrees.

Virtual classes for hypersurfaces via two-periodic complexes

These expository notes are based on a series of lectures given at the May 2018 Snowbird workshop, Crossing the Walls in Enumerative Geometry. We give an introductory treatment of the notion of a virtual fundamental class in algebraic geometry, and describe a new construction of the virtual fundamental class for Gromov-Witten theory of a hypersurface. The results presented here are based on joint work with I. Ciocan-Fontanine, D. Favero, J. Guéré, and B. Kim.

Ramblings on the freeness of affine hypersurfaces

In this note we look at the freeness for complex affine hypersurfaces. If $X \subset \mathbb{C}^n$ is such a hypersurface, and $D$ denotes the associated projective hypersurface, obtained by taking the closure of $X$ in $\mathbb{P}^n$, then we relate first the Jacobian syzygies of $D$ and those of $X$. Then we introduce two types of freeness for an affine hypersurface $X$, and prove various relations between them and the freeness of the projective hypersurface $D$. We write down a proof of the folklore result saying that an affine hypersurface is free if and only if all of its singularities ar…

Note on Milnor numbers of irreducible germs

Let $(\bf {V,0})\subset (\mathbb{C}^n,0)$ be a germ of a complex hypersurface and let $f: (\mathbb{C}^n,0)\to(\mathbb{C}^n,0)$ be a germ of a finite holomorphic mapping. If germs $(\bf {V,0})$ and ${\bf W}:=(F^{-1}(\bf{ V})),0)$ are irreducible and with isolated singularities, then $$μ(F^{-1}(\bf{ V}))\ge μ(\bf {V}),$$ where $μ$ denotes the Milnor number.

On the Brieskorn (a,b)-module of an hypersurface singularity

We show in this note that for a germ $g$ of holomorphic function with an isolated singularity at the origin of $\mathbb{C}^n$ there is a pole for the meromorphic extension of the distribution \begin{equation*} \frac{1}{Γ(λ)} \int_X | g |^{2λ}\bar{g}^{-n} \square \tag{*} \end{equation*} at $- n - α$ when $ α$ is the smallest root in its class modulo $\mathbb{Z}$ of the reduce Bernstein-Sato polynomial of $g$. This is rather unexpected result comes from the fact that the self-duality of the Brieskorn (a,b)-module $E_g$ associated to $g$ exchanges the biggest simple pole sub-(a,b)-module of $E_g$…

Some elementary examples of quartics with finite-dimensional motive

This small note contains some easy examples of quartic hypersurfaces that have finite-dimensional motive. As an illustration, we verify a conjecture of Voevodsky (concerning smash-equivalence) for some of these special quartics.

Entire holomorphic curves into projective spaces intersecting a generic hypersurface of high degree

In this note, we establish the following Second Main Theorem type estimate for every entire non-algebraically degenerate holomorphic curve $f\colon\mathbb{C}\rightarrow\mathbb{P}^n(\mathbb{C})$, in present of a {\sl generic} hypersuface $D\subset\mathbb{P}^n(\mathbb{C})$ of sufficiently high degree $d\geq 15(5n+1)n^n$: \[ T_f(r) \leq \,N_f^{[1]}(r,D) + O\big(\log T_f(r) + \log r \big)\parallel, \] where $T_f(r)$ and $N_f^{[1]}(r,D)$ stand for the order function and the $1$-truncated counting function in Nevanlinna theory. This inequality quantifies recent results on the logarithmic Green--Grif…

On Katz's bound for number of elements with given trace and norm

In this note an improvement of the Katz's bound on the number of elements in a finite field with given trace and norm is given. The improvement is obtained by reducing the problem to estimating the number of rational points on certain toric Calabi-Yau hypersurface, and then to use detailed cohomological calculations by Rojas-Leon and the second author for such toric hypersurfaces.

Calabi-Yau Varieties and Pencils of K3 Surfaces

In this note, we give a list of Calabi-Yau hypersurfaces in weighted projective 4-spaces with the property that a hypersurface contains naturally a pencil of K3 variety. For completeness we also obtain a similar list in the case K3 hypersurfaces in weighted projective 3-spaces. The first list significantly enlarges the list of K3-fibrations of \KlemmLercheMayr~ which has been obtained on some assumptions on the weights. Our lists are expected to correspond to examples of the so-called heterotic-type II duality \KachruVafa\KachruSilverstein.

Lectures on zeta functions over finite fields

These are the notes from the summer school in Göttingen sponsored by NATO Advanced Study Institute on Higher-Dimensional Geometry over Finite Fields that took place in 2007. The aim was to give a short introduction on zeta functions over finite fields, focusing on moment zeta functions and zeta functions of affine toric hypersurfaces.

Jacobian Newton Polyhedra and equisingularity

This is the LaTeX version of the handwritten notes of a lecture at the Kyoto Singularities Symposium held at the RIMS in April 1978. It presents the relationship of various invariants of isolated singularities of complex analytic hypersurfaces with the jacobian Newton polygon built from the polar curves. An appendix presents features of the semiring of Newton polygons, because the product of Jacobian Newton polygons corresponds to the Thom-Sebastiani sum of hypersurfaces. Analogies between mixed multiplicities and mixed volumes are noticed. They have been explained since.