Nash problem for surfaces

Nash modification on toric surfaces

It has been recently shown that the iteration of Nash modification on not necessarily normal toric varieties corresponds to a purely combinatorial algorithm on the generators of the semigroup associated to the toric variety. We will show that for toric surfaces this algorithm stops for certain choices of affine charts of the Nash modification. In addition, we give a bound on the number of steps required for the algorithm to stop in the cases we consider. Let $\C(x_1,x_2)$ be the field of rational functions of a toric surface. Then our result implies that if $ν:\C(x_1,x_2)\rightarrowΓ$ is any v…

On the Nash problem for surfaces in positive characteristic

This paper seeks to prove the bijectivity of the "Nash mapping" from the set of irreducible components of the scheme parametrizing analytic arcs on an algebraic surface $X$ whose origin is a singular point, into the set of irreducible components of the exceptional locus of a minimal desingularization $X'$ of $X$ when the base field has positive characteristic. The idea is to view the surface as a specialization of another defined over a field of characteristic zero. A number of related results are proved. Among them, the construction of a scheme of arcs for a suitable one parameter family of s…

On the generalized Nash problem for smooth germs and adjacencies of curve singularities

In this paper we explore the generalized Nash problem for arcs on a germ of smooth surface: given two prime divisors above its special point, to determine whether the arc space of one of them is included in the arc space of the other one. We prove that this problem is combinatorial and we explore its relation with several notions of adjacency of plane curve singularities.

A class of non-rational surface singularities with bijective Nash map

Let (S,0) be a germ of complex analytic normal surface. On its minimal resolution, we consider the reduced exceptional divisor E and its irreducible components E_i. The Nash map associates to each irreducible component C_k of the space of arcs through 0 on S the unique component of E cut by the strict transform of the generic arc in C_k. Nash proved its injectivity and asked if it was bijective. As a particular case of our main theorem, we prove that this is the case if E.E_i <0 for any i.

Factorization of normalization of Nash blow-up of order n of An by the minimal resolution

We show that the normalization of the Nash blow-up of order n of the toric surface singularity An can be factorized by the minimal resolution of An. The result is obtained using the combinatorial description of these objects.

The Nash problem on arcs for surface singularities

Let $(X,O)$ be a germ of a normal surface singularity, $π: \tilde X\longrightarrow X$ be the minimal resolution of singularities and let $A=(a_{i,j})$ be the $n\times n$ symmetrical intersection matrix of the exceptional set of $\tilde X$. In an old preprint Nash proves that the set of arcs on a surface singularity is a scheme ${\cal H}$, and defines a map ${\cal N}$ from the set of irreducible components of ${\cal H}$ to the set of exceptional components of the minimal resolution of singularities of $(X,O)$. He proved that this map is injective and ask if it is surjective. In this paper we co…

Nash problem for stable toric varieties

We present a solution for Nash problem for stable toric varieties. We also introduce Nash problem for pairs and prove it for toric pairs.

Résolution du problème des arcs de Nash pour une famille d'hypersurfaces quasi-rationnelles

The Nash problem on arcs for normal surface singularities states that there are as many arc families on a germ (S,O) of a singular surface as there are essential divisors over (S,O). It is known that this problem can be reduced to the study of quasi-rational singularities. In this paper we give a positive answer to the Nash problem for a family of non-rational quasi-rational hypersurfaces. The same method is applied to answer positively to this problem in the case of E_6 and E_7 type singularities, and to provide new proof in the case of D_n, n> =4, type singularities.

The Nash problem from a geometric and topological perspective

We survey the proof of the Nash conjecture for surfaces and show how geometric and topological ideas developed in previous articles by the authors influenced it. Later we summarize the main ideas in the higher dimensional statement and proof by de Fernex and Docampo. We end the paper by explaining later developments on generalized Nash problem and on Kollár and Nemethi's study about holomorphic arcs.

The Local Nash problem on arc families of singularities

This paper shows the affirmative answer to the local Nash problem for a toric singularity and analytically pretoric singularity. As a corollary we obtain the affirmative answer to the local Nash problem for a quasi-ordinary singularity.

素特征域中环面簇的Nash吹胀

Nash blowups of toric varieties in prime characteristic

本文研究素特征域上Nash吹胀的奇点消解性质，证明迭代规范化Nash吹胀可消解正规环面曲面奇点，并引入对数Jacobian理想的素特征版本以实现对任意维环面簇Nash吹胀的组合描述。

On the Nash problem for terminal threefolds of type $cA/r$

We study Nash valuations and essential valuations of terminal threefolds of type $cA/r$. If $r=1$ or the given threefold is $\mathbb Q$-factorial, then all the Nash valuations and essential valuations can be completely described. We construct non-Gorenstein or non-$\mathbb Q$-factorial counter examples for the Nash problem.

Bilipschitz几何：切锥为平面的实曲面奇点

Bilipschitz geometry of real surface singularities whose tangent cone is a plane

本文研究实曲面奇点在双Lipschitz等价下Nash锥与例外射线的行为，针对切锥为平面的孤立奇点情形。

The Nash problem for torus actions of complexity one

We solve the equivariant generalized Nash problem for any non-rational normal variety with torus action of complexity one. Namely, we give an explicit combinatorial description of the Nash order on the set of equivariant divisorial valuations on any such variety. Using this description, we positively solve the classical Nash problem in this setting, showing that every essential valuation is a Nash valuation. We also describe terminal valuations and use our results to answer negatively a question of de Fernex and Docampo by constructing examples of Nash valuations which are neither minimal nor …

Nash problem for a toric pair and the minimal log-discrepancy

This paper formulates the Nash problem for a pair consisting of a toric variety and an invariant ideal and gives an affirmative answer to the problem. We also prove that the minimal log-discrepacy is computed by a divisor corresponding to a Nash component, if the minimal log-discrepancy is finite. On the other hand there exists a Nash component such that the corresponding divisor has negative log-discrepancy, if the minimal log-discrepancy is $-/infty$.

Jet schemes, arc spaces and the Nash problem

This paper is an introduction to the jet schemes and the arc space of an algebraic variety. We also introduce the Nash problem on arc families.

The Nash problem on arc families of singularities

Nash proved that every irreducible component of the space of arcs through a singularity corresponds to an exceptional divisor that occurs on every resolution. He asked if the converse also holds: does every such exceptional divisor correspond to an arc family? We prove that the converse holds for toric singularities but fails in general.

The embedded Nash problem of birational models of rational triple singularities

We consider the question whether one can construct an embedded resolution of singularities of a singular variety $X\subset \textbf{A}^n$ from the data of the irreducible components of the spaces of jets (of $X$) centered at the singular locus of $X.$ We show that the answer is no in general and that it is yes for some birational models of rational triple surface singularities.

关于Pfaffian理想的单值性猜想、全纯性猜想与嵌入Nash问题

On the monodromy conjecture, holomorphy conjecture, and embedded Nash problem for Pfaffian ideals

本文解决了Pfaffian理想的单值性猜想、全纯性猜想以及嵌入Nash问题。

关于3折终端奇点类型cAx/2上的纳什问题

On the Nash Problem over 3-Fold Terminal Singularities of Type cAx/2

本文研究3折终端奇点类型cAx/2上的纳什估值，发现例外素数除子诱导纳什估值，并推测该结论适用于所有3折终端奇点。

Terminal valuations and the Nash problem

Let X be an algebraic variety of characteristic zero. Terminal valuations are defined in the sense of the minimal model program, as those valuations given by the exceptional divisors on a minimal model over X. We prove that every terminal valuation over X is in the image of the Nash map, and thus it corresponds to a maximal family of arcs through the singular locus of X. In dimension two, this result gives a new proof of the theorem of Fernández de Bobadilla and Pe Pereira stating that, for surfaces, the Nash map is a bijection.

关于嵌入Nash问题

On the embedded Nash problem

本文研究光滑代数簇中超曲面的嵌入Nash问题，证明对的最小模型上的除子与具有固定接触阶的弧族相关，并用消解图解决了单分支平面曲线胚的情形，作为经典Nash问题的嵌入类比。

关于纳什吹胀问题的计算方法

On a Computational Approach to the Nash Blowup Problem

本文通过计算方法发现纳什吹胀猜想的反例，并提供了无法通过标准化纳什吹胀解析的典范簇例子，同时展示了大量计算证据支持猜想的剩余开放案例。

The Nash problem of arcs and the rational double point $\mathbf{E_6}$

This paper deals with the Nash problem, which consists in proving that the number of families of arcs on a singular germ of a surface $S$ coincides with the number of irreducible components of the exceptional divisor in the minimal resolution of this singularity. We propose a program for an affirmative solution of the Nash problem in the case of normal 2-dimensional hypersurface singularities. We illustrate this program by giving an affirmative solution of the Nash problem for the rational double point $\mathbf{E_6}$. We also prove some results on the algebraic structure of the space of $k$-je…

Three-dimensional counter-examples to the Nash problem

The Nash problem asks about the existence of a correspondence between families of arcs through singularities of complex varieties and certain types of divisorial valuations. It has been positively settled in dimension 2 by Fernández de Bobadilla and Pe Pereira, and it was shown to have a negative answer in all dimensions $\ge 4$ by Ishii and Kollár. In this note we discuss examples which show that the problem has a negative answer in dimension 3 as well. These examples bring also to light the different nature of the problem depending on whether it is formulated the algebraic setting or in the …

On the polyhedral homotopy method for solving generalized Nash equilibrium problems of polynomials

The generalized Nash equilibrium problem (GNEP) is a kind of game to find strategies for a group of players such that each player's objective function is optimized. Solutions for GNEPs are called generalized Nash equilibria (GNEs). In this paper, we propose a numerical method for finding GNEs of GNEPs of polynomials based on the polyhedral homotopy continuation and the Moment-SOS hierarchy of semidefinite relaxations. We show that our method can find all GNEs if they exist, or detect the nonexistence of GNEs, under some genericity assumptions. Some numerical experiments are made to demonstrate…

A propos de la conjecture de Nash

This paper deals with the Nash problem, which claims that there are as many families of arcs on a singular germ of surface $U$ as there are essential components of the exceptional divisor in the desingularisation of this singularity. Let $\mathcal{H}=\bigcup \bar{N_α}$ be a particular decomposition of the set of arcs on $U$, described later on. We give two new conditions to insure that $\bar{N_α}\not \subset \bar{N_β}$, $α\not = β$; more precisely,for the first one, we claim that if there exists $f \in {\mathcal{O}}_{U}$ such that $ord_{E_α}(f)<ord_{E_β}(f)$, where $E_α, E_β$ are exceptional d…

Global bi-Lipschitz classification of semi-algebraic surfaces

We classify semi-algebraic surfaces in $\mathbb{R}^n$ with isolated singularities up to bi-Lipschitz homeomorphisms with respect to the inner distance. In particular, we obtain complete classifications for the Nash surfaces and the complex algebraic curves. We also address the minimal surfaces with finite total curvature.