arXiv subjects

Jérôme Poineau

Publications and source records attributed to Jérôme Poineau.

At least 19 recordsLinked to original sources

arXiv2025

Dynamique analytique sur $\mathbf{Z}$. I : Mesures d'équilibre sur une droite projective relative

Consider a Berkovich space over a good Banach ring and the relative projective line over it. (It is a space whose fibers are projective lines over different complete valued fields.) For each polarized endomorphism of this line, we prove that the family of equilibrium measures associated to the restrictions of the endomorphism to the fibers is continuous. The result holds, in particular, when the Banach ring is a complete valued field, a hybrid field, a complete discrete valuation ring, or the ring of integers of a number field.

math.DS↗

arXiv2025

Dynamique analytique sur $\mathbf{Z}$. II : Écart uniforme entre Lattès et conjecture de Bogomolov-Fu-Tschinkel

We prove that the mutual energy (or the intersection product in the sense of Arakelov theory) of two dynamical systems associated to Lattès morphisms over $\mathbf{\bar Q}$ is uniformly bounded below and deduce a proof of a conjecture of Bogomolov-Fu-Tschinkel: the number of common images of torsion points of two non-isomorphic elliptic curves over $\mathbf{C}$ by a standard morphism to the projective line is uniformly bounded. The proof crucially relies on the theory of Berkovich spaces over $\mathbf{Z}$ and on an original argument allowing to obtain a global estimate from a central estimate (over a trivially valued field).

math.NT↗

arXiv2025

Valuative compactifications of analytic varieties

Let $X$ be an algebraic variety over $\mathbf{C}$. We define a canonical compactification $X^{\!\urcorner}$ of the complex analytic space $X(\mathbf{C})$ by adding a Berkovich space over a trivially valued field at the boundary. The construction is functorial with respect to proper morphisms and preserves many properties, such as normality, regularity, etc. We prove a partial GAGA theorem in this setting : there is an equivalence between the categories of coherent sheaves on $X$ and $X^{\!\urcorner}$, and it induces bijections on global sections. The results still hold if $\mathbf{C}$ is replaced by a complete non-trivially valued field $k$, and complex analytic spaces by Berkovich analytic spaces over $k$.

math.AG↗

arXiv2025

Affine vs. Stein in rigid geometry

We investigate the relationship between affine and Stein varieties in the context of rigid geometry. We show that the two concepts are much more closely related than in complex geometry, e.g. they are equivalent for surfaces. This rests on the density of algebraic functions in analytic functions. One key ingredient to prove such a density statement is an extension result for Cartier divisors.

math.AG↗

arXiv2024

The convergence Newton polygon of a $p$-adic differential equation IV : controlling graphs

In our previous works we proved a finiteness property of the radii of convergence functions associated with a vector bundle with connection on $p$-adic analytic curves. We showed that the radii are locally constant functions outside a locally finite graph in the curve, called controlling graph. In this paper we refine that finiteness results by giving a bound on the size of the controlling graph in terms of the geometry of the curve and the rank of the module. This is based on super-harmonicity properties of radii of convergence and partial heights of the Newton polygon. Under suitable assumptions, we relate the size of the controlling graph associated with the total height of the convergence Newton polygon to the Euler characteristic in the sense of de Rham cohomology.

math.NT↗

arXiv2024

The convergence Newton polygon of a $p$-adic differential equation V : local index theorems

In this paper and its sequel we consider locally-free $\mathscr{O}_X$-modules together with a connection over a quasi-smooth Berkovich curve $X$. We obtain necessary and sufficient conditions for the finite dimensionality of their de Rham cohomology over local domains such as disks and annuli. We deal with both analytic and meromorphic connections and we derive index formulas relating the index to the behavior of the radii of convergence of their solutions at the boundary of the curve $X$. We introduce the notion of absolute local index. We prove that it is an intrinsic notion extending the previous notions of Robba's generalized index and that of $p$-adic exponents. This condition arises at the boundary of the curve $X$ and it is an exact condition for the finite dimensionality of the de Rham cohomology. We derive comparison results between formal, meromorphic and analytic de Rham cohomologies.

math.NT↗

arXiv2024

The convergence Newton polygon of a $p$-adic differential equation III : global decompositions

We deal with locally free $\mathcal{O}_X$-modules with connection over a Berkovich curve $X$. As a main result we prove local and global decomposition theorems of such objects by the radii of convergence of their solutions. We also derive a bound of the number of edges of the controlling graph, in terms of the geometry of the curve and the rank of the equation. As an application we provide a classification result of such equations over elliptic curves.

math.NT↗

arXiv2024

Espaces de Berkovich globaux : catégorie, topologie, cohomologie

This text contributes to the foundations of the theory of global Berkovich spaces, that is to say Berkovich spaces over Banach rings with nice properties such as $\mathbf{Z}$, rings of integers of number fields, discrete valuation rings, hybrid fields, etc. We focus on three main themes that had not been investigated so far: category, topology and cohomology. As regards the category, our main task is to define a well-behaved notion of morphism. We then have the suitable setting at our disposal to carry out and study various constructions: products, fiber products, extensions of scalars, analytification of schemes, etc. On the topological side, we show that global Berkovich spaces are locally path-connected. The main ingredient is an analogue of Noether's normalization lemma, that we obtain after a careful study of finite morphisms. Finally, we prove that open and closed discs of arbitrary dimension have no higher coherent cohomology. This is a deep result, which allows us to initiate a theory of global overconvergent affinoid spaces, where the analogues of Tate's and Kiehl's theorems hold. As a consequence of our vanishing statements, we obtain a geometric proof of a Noetherianity result for certain rings of convergent arithmetic power series (power series with integral coefficients and positive complex radii of convergence), generalizing a theorem of D. Harbater from the case of a single variable to arbitrary many.

math.AG↗

arXiv2021

Schottky spaces and universal Mumford curves over $\mathbb{Z}$

For every integer $g \geq 1$ we define a universal Mumford curve of genus $g$ in the framework of Berkovich spaces over $\mathbb{Z}$. This is achieved in two steps: first, we build an analytic space $\mathcal{S}_g$ that parametrizes marked Schottky groups over all valued fields. We show that $\mathcal{S}_g$ is an open, connected analytic space over $\mathbb{Z}$. Then, we prove that the Schottky uniformization of a given curve behaves well with respect to the topology of $\mathcal{S}_g$, both locally and globally. As a result, we can define the universal Mumford curve $\mathcal{C}_g$ as a relative curve over $\mathcal{S}_g$ such that every Schottky uniformized curve can be described as a fiber of a point in $\mathcal{S}_g$. We prove that the curve $\mathcal{C}_g$ is itself uniformized by a universal Schottky group acting on the relative projective line $\mathbb{P}^1_{\mathcal{S}_g}$. Finally, we study the action of the group $Out(F_g)$ of outer automorphisms of the free group with $g$ generators on $\mathcal{S}_g$, describing the quotient $Out(F_g) \backslash \mathcal{S}_g$ in the archimedean and non-archimedean cases. We apply this result to compare the non-archimedean Schottky space with constructions arising from geometric group theory and the theory of moduli spaces of tropical curves.

math.AG↗

arXiv2020

Berkovich curves and Schottky uniformization

This text is an exposition of non-Archimedean curves and Schottky uniformization from the point of view of Berkovich geometry. It consists of two parts, the first one of an introductory nature, and the second one more advanced. The first part is meant to be an introduction to the theory of Berkovich spaces focused on the case of the affine line. We define the Berkovich affine line and present its main properties, with many details: classification of points, path-connectedness, metric structure, variation of rational functions, etc. Contrary to many other introductory texts, we do not assume that the base field is algebraically closed. The second part is devoted to the theory of Mumford curves and Schottky uniformization. We start by briefly reviewing the theory of Berkovich curves, then introduce Mumford curves in a purely analytic way (without using formal geometry). We define Schottky groups acting on the Berkovich projective line, highlighting how geometry and group theory come together to prove that the quotient by the action of a Schottky group is an analytic Mumford curve. Finally, we present an analytic proof of Schottky uniformization, showing that any analytic Mumford curves can be described as a quotient of this kind. The guiding principle of our exposition is to stress notions and fully prove results in the theory of non-Archimedean curves that, to our knowledge, are not fully treated in other texts.

math.AG↗

arXiv2019

Definable sets of Berkovich curves

In this article, we functorially associate definable sets to $k$-analytic curves, and definable maps to analytic morphisms between them, for a large class of $k$-analytic curves. Given a $k$-analytic curve $X$, our association allows us to have definable versions of several usual notions of Berkovich analytic geometry such as the branch emanating from a point and the residue curve at a point of type 2. We also characterize the definable subsets of the definable counterpart of $X$ and show that they satisfy a bijective relation with the radial subsets of $X$. As an application, we recover (and slightly extend) results of Temkin concerning the radiality of the set of points with a given prescribed multiplicity with respect to a morphism of $k$-analytic curves. In the case of the analytification of an algebraic curve, our construction can also be seen as an explicit version of Hrushovski and Loeser's theorem on iso-definability of curves. However, our approach can also be applied to strictly $k$-affinoid curves and arbitrary morphisms between them, which are currently not in the scope of their setting.

math.AG↗

arXiv2019

The convergence Newton polygon of a p-adic differential equation II: Continuity and finiteness on Berkovich curves

We study the variation of the convergence Newton polygon of a differential equation along a smooth Berkovich curve over a non-archimedean complete valued field of characteristic 0. Relying on work of the second author who investigated its properties on affinoid domains of the affine line, we prove that its slopes give rise to continuous functions that factorize by the retraction through a locally finite subgraph of the curve.

math.NT↗

arXiv2018

Notions of Stein spaces in non-archimedean geometry

Let $k$ be a non-archimedean complete valued field and $X$ be a $k$-analytic space in the sense of Berkovich. In this note, we prove the equivalence between three properties: 1) for every complete valued extension $k'$ of $k$, every coherent sheaf on $X \times_{k} k'$ is acyclic; 2) $X$ is Stein in the sense of complex geometry (holomorphically separated, holomorphically convex) and higher cohomology groups of the structure sheaf vanish (this latter hypothesis is crucial if, for instance, $X$ is compact); 3) $X$ admits a suitable exhaustion by compact analytic domains considered by Liu in his counter-example to the cohomological criterion for affinoidicity. When $X$ has no boundary the characterization is simpler: in~2) the vanishing of higher cohomology groups of the structure sheaf is no longer needed, so that we recover the usual notion of Stein space in complex geometry; in 3) the domains considered by Liu can be replaced by affinoid domains, which leads us back to Kiehl's definition of Stein space. v2: major revision to handle also the case of spaces with boundary

math.AG↗

arXiv2018

Pushforwards of $p$-adic differential equations

Given a differential equation on a smooth $p$-adic analytic curve, one may construct a new one by pushing forward by an étale morphism. The main result of the paper provides an explicit formula that relates the radii of convergence of the solutions of the two differential equations using invariants coming from the topological behavior of the morphism. We recover as particular cases the known formulas for Frobenius morphisms and tame morphisms. As an application, we show that the radii of convergence of the pushforward of the trivial differential equation at a point coincide with the upper ramification jumps of the extension of the residue field of the point given by the morphism. We also derive a general formula computing the Laplacian of the height of the Newton polygon of a $p$-adic differential equation.

math.NT↗

arXiv2018

On the number of connected components of the ramification locus of a morphism of Berkovich curves

Let $k$ be a complete, nontrivially valued non-archimedean field. Given a finite morphism of quasi-smooth $k$-analytic curves that admit finite triangulations, we provide upper bounds for the number of connected components of the ramification locus in terms of topological invariants of the source curve such as its topological genus, the number of points in the boundary and the number of open ends.

math.AG↗

arXiv2014

Sur les composantes connexes d'une famille d'espaces analytiques p-adiques

Let $X=\mathcal{M}(A)$ be an affinoid space and let $f,g \in A$. We study the sets of connected components of the spaces defined by an inequality of the form $|f|\le r|g|$, with $r\ge 0$. We prove that there exists a finite partition of $\mathbb{R}_+$ into intervals where those sets are canonically in bijection and that the bounds of those intervals belong to $\sqrt{ρ(A)}$.

math.NT↗

arXiv2012

Les espaces de Berkovich sont angéliques

Although Berkovich spaces may fail to be metrizable when defined over too big a field, we prove that a large part of their topology can be recovered through sequences: for instance, limit points of subsets are actual limits of sequences and compact subsets are sequentially compact. Our proof uses extension of scalars in an essential way and we need to investigate some of its properties. We show that a point in a disc may be defined over a subfield of countable type and that, over algebraically closed fields, every point is universal: in an extension of scalars, it may be canonically lifted.

math.AG↗

arXiv2012

Espaces de Berkovich sur Z : étude locale

We investigate the local properties of Berkovich spaces over Z. Using Weierstrass theorems, we prove that the local rings of those spaces are noetherian, regular in the case of affine spaces and excellent. We also show that the structure sheaf is coherent. Our methods work over other base rings (valued fields, discrete valuation rings, rings of integers of number fields, etc.) and provide a unified treatment of complex and p-adic spaces.

math.AG↗