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We show that, conditional on Zywina's effective version of the Serre uniformity conjecture, there is a natural way to parameterize non-CM $\mathbb{Q}$-rational points on all modular curves in terms of the rational points on finitely many…

Number Theory · Mathematics 2026-03-10 Maarten Derickx , Sachi Hashimoto , Filip Najman , Ari Shnidman

We study families of rational curves on an algebraic variety satisfying incidence conditions. We prove an analogue of bend-and-break: that is, we show that under suitable conditions, such a family must contain reducibles. In the case of…

Algebraic Geometry · Mathematics 2020-06-26 Ziv Ran

We give a closed formula for the dimension of all linear systems in $\mathbb{P}^n$ with assigned multiplicity at arbitrary collections of points lying on a rational normal curve of degree $n$. In particular we give a purely geometric…

Algebraic Geometry · Mathematics 2022-05-10 Antonio Laface , Elisa Postinghel , Luis José Santana Sánchez

Working in positive characteristic, we show how one can use information about the dimension of moduli spaces of rational curves on a Fano variety $X$ over $\mathbb{F}_q$ to obtain strong estimates for the number of $\mathbb{F}_q(t)$-points…

Number Theory · Mathematics 2025-05-13 Jakob Glas

We prove that the spaces of rational curves on del Pezzo surfaces are either irreducible or empty, with a unique exception.

Algebraic Geometry · Mathematics 2007-05-23 Damiano Testa

We investigate the spaces of rational curves on a general hypersurface. In particular, we show that for a general degree $d$ hypersurface in $\mathbb{P}^n$ with $n \geq d+2$, the space $\overline{\mathcal{M}_{0,0}}(X,e)$ of degree $e$…

Algebraic Geometry · Mathematics 2016-10-05 Eric Riedl , David Yang

We construct the canonical structure of an irreducible projective variety on the set of connected curves of degree $d$ in $\Bbb P^n$ with rational components (some components can be multiple). The set of rational curves is open subset in…

Algebraic Geometry · Mathematics 2007-05-23 Pavel Katsylo

In this paper we investigate complex uniruled varieties $X$ whose rational curves of minimal degree satisfy a special property. Namely, we assume that the tangent directions to such curves at a general point $x\in X$ form a linear subspace…

Algebraic Geometry · Mathematics 2007-05-23 Carolina Araujo

In projective space over fields of characteristic different from 2, the normal bundle of a general nondegenerate rational curve is balanced. The corresponding statement for rational curves in other Grassmannians can fail. Nevertheless, we…

Algebraic Geometry · Mathematics 2024-04-15 Izzet Coskun , Eric Larson , Isabel Vogt

We study singular rational curves in projective space, deducing conditions on their parametrizations from the value semigroups $\sss$ of their singularities. In particular, we prove that a natural heuristic for the codimension of the space…

Algebraic Geometry · Mathematics 2019-09-27 Ethan Cotterill , Lia Feital , Renato Vidal Martins

We proved the existence of rational curves in every linear system on a general K3 surface and that all rational curves in the hyperplane class are nodal on a general K3 surface of small genus.

Algebraic Geometry · Mathematics 2007-05-23 Xi Chen

In this paper the notion of rational simple connectedness for the quintic Fano threefold $V_5\subset \mathbb{P}^6$ is studied and unirationality of the moduli spaces $\overline{M}_{0,0}^{\text{bir}}(V_5,d)$, with $d \ge 1$, is proved. Many…

Algebraic Geometry · Mathematics 2019-01-23 Andrea Fanelli , Laurent Gruson , Nicolas Perrin

In the present survey we collect some recent results on nuclei of Veronese varieties and invariant subspaces of normal rational curves. We must assume, however, that the ground field is not "too small", since otherwise a Veronese variety is…

Algebraic Geometry · Mathematics 2024-02-13 Hans Havlicek

Consider the scheme parametrizing non-constant morphisms from a fixed projective curve to a projective surface. There is a rational map between this scheme and the Chow variety of $1$-cycles on the surface. We prove that, if the curve is…

Algebraic Geometry · Mathematics 2020-11-03 Lucas das Dores

The Newton polygon of the implicit equation of a rational plane curve is explicitly determined by the multiplicities of any of its parametrizations. We give an intersection-theoretical proof of this fact based on a refinement of the…

Algebraic Geometry · Mathematics 2010-02-24 Carlos D'Andrea , Martin Sombra

Given a morphism between smooth projective varieties $f: W \to X$, we study whether $f$-relatively free rational curves imply the existence of $f$-relatively very free rational curves. The answer is shown to be positive when the fibers of…

Algebraic Geometry · Mathematics 2010-05-10 Matt DeLand

We establish a general superposition principle for curves of measures solving a continuity equation on metric spaces without any smooth structure nor underlying measure, representing them as marginals of measures concentrated on the…

Functional Analysis · Mathematics 2015-12-17 Eugene Stepanov , Dario Trevisan

We classify all complex surfaces with quotient singularities that do not contain any smooth rational curves, under the assumption that the canonical divisor of the surface is not pseudo-effective. As a corollary we show that if $X$ is a log…

Algebraic Geometry · Mathematics 2018-10-17 Ziquan Zhuang

We introduce arrangements of rational sections over curves. They generalize line arrangements on P^2. Each arrangement of d sections defines a single curve in P^{d-2} through the Kapranov's construction of \bar{M}_{0,d+1}. We show a…

Algebraic Geometry · Mathematics 2011-04-05 Giancarlo Urzua

This paper is concerned with rational curves on real classical groups. Our contributions are three-fold: (i) We determine the structure of quadratic rational curves on real classical groups. As a consequence, we completely classify…

Algebraic Geometry · Mathematics 2024-08-09 Zijia Li , Ke Ye