Even sets of four nodes on rational surfaces

Even sets of nodes and Gauss genus theory

We observe that a lemma used in the study of even sets of nodes on surfaces applies almost verbatim to prove a celebrated formula of Gauss on the 2-torsion of the class group of a quadratic field.

弱接触圆锥与具有2个节点和1个尖点的不可约四次曲线的几何学 via 理性椭圆面和扎里斯基对

Geometry of weak contact conics to irreducible quartics with 2 nodes and 1 cusp via rational elliptic surfaces and Zariski pairs

研究弱接触圆锥与具有2个节点和1个尖点的不可约四次曲线的几何结构，通过理性椭圆面和扎里斯基对构造度数为7和8的扎里斯基对。

Surfaces with many nodes

We describe smooth rational projective algebraic surfaces over an algebraically closed field of characteristic different from 2 which contain $n \ge \b_2-2$ disjoint smooth rational curves with self-intersection -2, where $\b_2$ is the second Betti number. In the last section this is applied to the study of minimal complex surfaces of general type with $p_g = 0$ and $K^2 = 8, 9$ which admit an automorphism of order 2.

Characteristic numbers of rational nodal curves in $\mathbb{P}^3$

In this paper we compute the number of rational curves with one node passing through a given number of points, lines and tangent to a given number of planes in $\mathbb{P}^3$.

Rational pencils of cubics and configurations of six or seven points in $\mathbb{R}P^2$

Let six points $1, ...6$ lie in general position in the real projective plane and consider the pencil of nodal cubics based at these points, with node at one of them, say 1. This pencil has five reducible cubics. We call combinatorial cubic a topological type (cubic, points), and combinatorial pencil the cyclic sequence of five combinatorial reducible cubics. Up to the action of the symmetric group $S_5$ on $\{2, ...6\}$, there are seven possible combinatorial pencils with node at 1. Consider now the set of six pencils obtained, making the node to be $1, ...6$. Up to the action of S_6 on ${1, …

Higher-dimensional Calabi-Yau varieties with dense sets of rational points

We construct higher-dimensional Calabi-Yau varieties defined over a given number field with Zariski dense sets of rational points. We give two elementary constructions in arbitrary dimensions as well as another construction in dimension three which involves certain Calabi-Yau threefolds containing an Enriques surface. The constructions also show that potential density holds for (sufficiently) general members of the families.

Maximally inflected real rational curves

We introduce and begin the topological study of real rational plane curves, all of whose inflection points are real. The existence of such curves is a corollary of results in the real Schubert calculus, and their study has consequences for the important Shapiro and Shapiro conjecture in the real Schubert calculus. We establish restrictions on the number of real nodes of such curves and construct curves realizing the extreme numbers of real nodes. These constructions imply the existence of real solutions to some problems in the Schubert calculus. We conclude with a discussion of maximally infle…

The integral Chow ring of the stack of at most 1-nodal rational curves

We give a presentation for the stack of rational curves with at most 1 node as the quotient by GL(3) of an open set in a 6-dimensional irreducible representation. We then use equivariant intersection theory to calculate the integral Chow ring of this stack.

有理点在六次双固体上的潜在稠密性

Potential density of rational points on sextic double solids

本文构造了特征零域上光滑六次双固体的例子，证明其有理点集合具有潜在稠密性。

Galois点与具有小值集的有理函数

Galois points and rational functions with small value sets

本研究建立了Galois点与有限域上小值集有理函数的联系，证明含双Galois点的平面曲线定义多项式的相关性质，打通了两个研究方向的关联。

A Ganzstellensatz for semi-algebraic sets and a boundedness criterion for rational functions

Let $\langle K,ν\rangle$ be a real closed valued field, and let $S\subseteq K^n$ be an open semi-algebraic set. Using tools from model theory, we find an algebraic characterization of rational functions which admit, on $S$, only values in the valuation ring. We use this result to deduce a criterion for a rational function to be bounded on an open semi algebraic subset of some irreducible variety over a real closed field or over an ordered field which is dense in its real closure.

具有有理同伦圆盘光滑化的正规曲面奇点

Normal complex surface singularities with rational homology disk smoothings

本文证明极小好预解图至少含两个节点的正规曲面奇点无有理同伦圆盘光滑化，结合已有分类结果给出此类奇点的完整分类，同时证明了Wahl猜想及其有理猜想。

Minimal even sets of nodes

We extend some results on even sets of nodes which have been proved for surfaces up to degree 6 to surfaces up to degree 10. In particular, we give a formula for the minimal cardinality of a nonempty even set of nodes.

Rationality of the moduli spaces of 2-elementary K3 surfaces

K3 surfaces with non-symplectic involution are classified by open sets of seventy-five arithmetic quotients of type IV. We prove that those moduli spaces are rational except two classical cases.

Missing sets in rational parametrizations of surfaces of revolution

Parametric representations do not cover, in general, the whole geometric object that they parametrize. This can be a problem in practical applications. In this paper we analyze the question for surfaces of revolution generated by real rational profile curves, and we describe a simple small superset of the real zone of the surface not covered by the parametrization. This superset consists, in the worst case, of the union of a circle and the mirror curve of the profile curve.

Rational points in periodic analytic sets and the Manin-Mumford conjecture

We present a new proof of the Manin-Mumford conjecture about torsion points on algebraic subvarieties of abelian varieties. Our principle, which admits other applications, is to view torsion points as rational points on a complex torus and then compare (i) upper bounds for the number of rational points on a transcendental analytic variety (Bombieri-Pila-Wilkie) and (ii) lower bounds for the degree of a torsion point (Masser), after taking conjugates. In order to be able to deal with (i), we discuss (Thm. 2.1) the semi-algebraic curves contained in an analytic variety supposed invariant for tra…

刚性解析集的有理点：一个Pila-Wilkie型定理

Rational points of rigid-analytic sets: a Pila-Wilkie type theorem

该研究建立Pila-Wilkie计数定理的刚性解析版本，给出$\u211a_p$-解析集超越部分有理解点、$\u2119_q((t))$-解析集有理函数的次多项式上界，并证明$\u2124[[t]]$-解析集的这类界对所有非阿基米德局部域特化一致成立。

A solution of the Erdos-Ulam problem on rational distance sets assuming the Bombieri-Lang conjecture

A rational distance set in the plane is a point set which has the property that all pairwise distances between its points are rational. Erd\H os and Ulam conjectured in 1945 that there is no dense rational distance set in the plane. In this paper we associate an algebraic surface in $\mathbb{P}^3$, that we call a distance surface, to any finite rational distance set in the plane. Under a mild condition, we prove that a distance surface is always a surface of general type. From this, we deduce that the Bombieri-Lang conjecture in arithmetic algebraic geometry (restricted to the classes of surfa…

Rational certificates of positivity on compact semialgebraic sets

Schmüdgen's Theorem says that if a basic closed semialgebraic set K = {g_1 \geq 0, ..., g_s \geq 0} in R^n is compact, then any polynomial f which is strictly positive on K is in the preordering generated by the g_i's. Putinar's Theorem says that under a condition stronger than compactness, any f which is strictly positive on K is in the quadratic module generated by the g_i's. In this note we show that if the g_i's and the f have rational coefficients, then there is a representation of f in the preordering with sums of squares of polynomials over Q. We show that the same is true for Putinar's…

Level curve portraits of rational inner functions

We analyze the behavior of rational inner functions on the unit bidisk near singularities on the distinguished boundary $\mathbb{T}^2$ using level sets. We show that the unimodular level sets of a rational inner function $ϕ$ can be parametrized with analytic curves and connect the behavior of these analytic curves to that of the zero set of $ϕ$. We apply these results to obtain a detailed description of the fine numerical stability of $ϕ$: for instance, we show that $\frac{\partial ϕ}{\partial z_1}$ and $\frac{\partial ϕ}{\partial z_2}$ always possess the same $L^{\mathfrak{p}}$-integrability …

Rational distance sets on a parabola using Pythagorean triplets

We study $N$-point rational distance sets ($\textrm{RDS}(N)$) on the parabola $y=x^2$. Previous approaches to the problem include efforts made using elliptic curves and diophantine chains, with successful analysis for $N\leq 4$. We extend the analysis for arbitrary $N$ by establishing a correspondence between $\textrm{RDS}(N)$s and Pythagorean triplets. Our main result gives sufficient and necessary conditions for the existence and nature of the $\textrm{RDS}(N)$s for arbitrary $N$. Our approach also leads to an efficient computational algorithm to construct new $\textrm{RDS}(N)$s, and we prov…

Rational blow-downs and smoothings of surface singularities

In this paper we give a necessary combinatorial condition for a negative--definite plumbing tree to be suitable for rational blow--down, or to be the graph of a complex surface singularity which admits a rational homology disk smoothing. New examples of surface singularities with rational homology disk smoothings are also presented; these include singularities with resolution graph having valency four nodes.

First Order Conditions for Semidefinite Representations of Convex Sets Defined by Rational or Singular Polynomials

A set is called semidefinite representable or semidefinite programming (SDP) representable if it can be represented as the projection of a higher dimensional set which is represented by some Linear Matrix Inequality (LMI). This paper discuss the semidefinite representability conditions for convex sets of the form S_D(f) = {x \in D: f(x) >= 0}. Here D={x\in R^n: g_1(x) >= 0, ..., g_m(x) >= 0} is a convex domain defined by some "nice" concave polynomials g_i(x) (they satisfy certain concavity certificates), and f(x) is a polynomial or rational function. When f(x) is concave over \mc{D}, we prove…

Dual certificates and efficient rational sum-of-squares decompositions for polynomial optimization over compact sets

We study the problem of computing weighted sum-of-squares (WSOS) certificates for positive polynomials over a compact semialgebraic set. Building on the theory of interior-point methods for convex optimization, we introduce the concept of dual cone certificates, which allows us to interpret vectors from the dual of the sum-of-squares cone as rigorous nonnegativity certificates of a WSOS polynomial. Whereas conventional WSOS certificates are alternative representations of the polynomials they certify, dual certificates are distinct from the certified polynomials; moreover, each dual certificate…