Searcharxiv⌕ Search

arXiv subjects

Harry Schmidt

Publications and source records attributed to Harry Schmidt.

18 recordsLinked to original sources
arXiv2026

Dynamical Canonical Heights and Finite Trees

We establish lower bounds for the canonical height of a wandering point that decays like the square of the field degree. Our methods and results apply to centered, postcritically finite, hyperbolic polynomials of prime power degree whose coefficients are algebraic integers. Our approach is ultimately inspired by an idea of Dimitrov that led to his proof of the Schinzel--Zassenhaus Conjecture. The height lower bound is derived from the lower bound of the local canonical height at an archimedean place. In previous work, the authors used a result of Dubinin on the transfinite diameter of a star-shaped tree. In this paper, we develop tools to bound the transfinite diameter of more general finite trees in the complex plane. We construct these trees using the Hubbard tree of a postcritically finite polynomial. Thurston's notion of core entropy helps us analyze combinatorial properties of the Hubbard tree.

math.NT↗
arXiv2026

Uniform sum-product phenomenon for algebraic groups and Bremner's conjecture

In this paper we combine methods from additive combinatorics and Diophantine geometry to study the generalised sum-product phenomenon in algebraic groups. As an application of this circle of ideas, we resolve a conjecture of Bremner on arithmetic progressions in coordinates of elliptic curves, along with various other generalisations studied in the literature. We also prove a uniform Bourgain--Chang-type sum-product estimate for general $1$-dimensional algebraic groups $G$ over $\mathbb{C}$. Using these ideas, we provide an alternative solution to a problem of Bays--Breuillard. Furthermore, we show an Elekes--Szab\'{o} type result in the same setting for sets with small doubling, improving upon an earlier result of Bays--Breuillard when $G$ is not $\mathbb{G}_a$. Our power saving here can be shown to be quantitatively optimal. We use a combination of deep, classical results in Diophantine geometry due to David--Philippon, Laurent and Evertse--Schmidt--Schlickewei along with the recent breakthrough work on the weak Polynomial Freiman--Ruzsa conjecture over integers due to Gowers--Green--Manners--Tao.

math.NT↗
arXiv2023

On the Manin-Mumford Theorem for Algebraic Groups

We describe the Zariski-closure of sets of torsion points in connected algebraic groups. This is a generalization of the Manin-Mumford conjecture for commutative algebraic groups proved by Hindry. He proved that every subset with Zariski-dense torsion points is the finite union of torsion-translates of algebraic subgroups. We formulate and prove an analogous theorem for arbitrary connected algebraic groups. We also define a canonical height on connected algebraic groups that coincides with a N\'eron-Tate height if $G$ is a (semi-) abelian variety. This motivates a generalization of the Bogomolov conjecture to arbitrary connected algebraic groups defined over a number field. We prove such a generalization as well.

math.NT↗
arXiv2023

An effective Pila-Wilkie theorem for sets definable using Pfaffian functions, with some diophantine applications

We prove an effective version of the Pila-Wilkie Theorem for sets definable using Pfaffian functions, providing effective estimates for the number of algebraic points of bounded height and degree lying on such sets. We also prove effective versions of extensions of this result due to Pila and Habegger-Pila . In order to prove these counting results, we obtain an effective version of Yomdin-Gromov parameterization for sets defined using restricted Pfaffian functions. Furthermore, for sets defined in the restricted setting, as well as for unrestricted sub-Pfaffian sets, our effective estimates depend polynomially on the degree (one measure of complexity) of the given set. The level of uniformity present in all the estimates allows us to obtain several diophantine applications. These include an effective and uniform version of the Manin-Mumford conjecture for products of elliptic curves with complex multiplication, and an effective, uniform version of a result due to Habegger which characterizes the set of special points lying on an algebraic variety contained in a fibre power of an elliptic surface. We also show that if Andr\'e-Oort for $Y(2)^g$ can be made effective, then Andr\'e-Oort for a family of elliptic curves over $Y(2)^g$ can be made effective.

math.NT↗
arXiv2022

Height coincidences in products of the projective line

We consider hypersurfaces in $(\mathbb{P}^1)^n$ that contain a generic sequence of small dynamical height with respect to a split map and project onto $n-1$ coordinates. We show that these hypersurfaces satisfy strong coincidence relations between their points with zero height coordinates. More precisely, it holds that in a Zariski-open dense subset of such a hypersurface $n-1$ coordinates have height zero if and only if all coordinates have height zero. This is a key step in the resolution of the dynamical Bogomolov conjecture for split maps.

math.NT↗
arXiv2022

On the dynamical Bogomolov conjecture for families of split rational maps

We prove that Zhang's dynamical Bogomolov conjecture holds uniformly along $1$-parameter families of rational split maps and curves. This provides dynamical analogues of recent results of Dimitrov-Gao-Habegger and K\"uhne. In fact, we prove a stronger Bogomolov-type result valid for families of split maps in the spirit of the relative Bogomolov conjecture. We thus provide first instances of a generalization of a conjecture by Baker and DeMarco to higher dimensions. Our proof contains both arithmetic and analytic ingredients. We establish a characterization of curves that are preperiodic under the action of a non-exceptional split rational endomorphism $(f,g)$ of $(\mathbb{P}^1_{\mathbb{C}})^2$ with respect to the measures of maximal entropy of $f$ and $g$, extending a previous result of Levin-Przytycki. We further establish a height inequality for families of split maps and varieties comparing the values of a fiber-wise Call-Silverman canonical height with a height on the base and valid for most points of a non-preperiodic variety. This provides a dynamical generalization of a result by Habegger and generalizes results of Call-Silverman and Baker to higher dimensions. In particular, we establish a geometric Bogomolov theorem for split rational maps and varieties of arbitrary dimension.

math.NT↗
arXiv2021

Lower Bounds for the Canonical Height of a Unicritical Polynomial and Capacity

In a recent breakthrough, Dimitrov solved the Schinzel-Zassenhaus Conjecture. We follow his approach and adapt it to certain dynamical systems arising from polynomials of the form $T^p+c$ where $p$ is a prime number and where the orbit of $0$ is finite. For example, if $p=2$, and $0$ is periodic under $T^2+c$ with $c\in\mathbb{R}\smallsetminus\{-2\}$, we prove a lower bound for the local canonical height of a wandering algebraic integer that is inversely proportional to the field degree. From this we are able to deduce a lower bound for the canonical height of a wandering point that decays like the inverse square of the field degree.

math.NT↗
arXiv2021

Unlikely Intersections of Curves with Algebraic Subgroups in Semiabelian Varieties

Let $G$ be a semiabelian variety and $C$ a curve in $G$ that is not contained in a proper algebraic subgroup of $G$. In this situation, conjectures of Pink and Zilber imply that there are at most finitely many points contained in the so-called unlikely intersections of $C$ with subgroups of codimension at least $2$. In this note, we establish this assertion for general semiabelian varieties over $\bar{\mathbb{Q}}$. This extends results of Maurin and Bombieri, Habegger, Masser, and Zannier in the toric case as well as Habegger and Pila in the abelian case.

math.NT↗
arXiv2021

Lower bounds for Galois orbits of special points on Shimura varieties: a point-counting approach

Let $S$ be a Shimura variety and let $h$ be a Weil height function on $S$. We conjecture that the heights of special points in $S$ are discriminant negligible. Assuming this conjecture to be true, we prove that the sizes of the Galois orbits of special points grow as a fixed power of their discriminant (an invariant we will define in the text). In the case of Shimura varieties of abelian type, the height bound holds by the recently proved averaged Colmez formula, and our theorem gives a new proof of Tsimerman's Galois lower bound in this case. The main novelty is that our approach avoids the use of Masser-W\"ustholz isogeny estimates, replacing them by a point-counting argument, and establishes lower bounds for Galois orbits conditional on height bounds for \emph{arbitrary} Shimura varieties. In particular, following the Pila-Zannier strategy (and Gao's work in the mixed case) this implies that the Andre-Oort conjecture for an arbitrary (mixed) Shimura variety follows from the corresponding conjecture on heights of special points.

math.NT↗
arXiv2020

Polynomial dynamics and local analysis of small and grand orbits

We prove an analogue of the Manin-Mumford conjecture for polynomial dynamical systems over number fields. In our setting the role of torsion points is taken by the small orbit of a point $\alpha$. The small orbit of a point was introduced by McMullen and Sullivan in their study of the dynamics of rational maps where for a point $\alpha$ and a polynomial $f$ it is given by \begin{align*} \mathcal{S}_\alpha = \{\beta \in \mathbb{C}; f^{\circ n}(\beta) = f^{\circ n}(\alpha) \text{ for some } n \in \mathbb{Z}_{\geq 0}\}. \end{align*} Our main theorem is a classification of the algebraic relations that hold between infinitely pairs of points in $\mathcal{S}_\alpha$ when everything is defined over the algebraic numbers and the degree $d$ of $f$ is at least 2. Our proof relies on a careful study of localizations of the dynamical system and follows an entirely different approach than previous proofs in this area. At infinite places of $K$ we use known rigidity theorems of Fatou and Levin to prove new such. These might be of independent interest in complex dynamics. At finite places we introduce new non-archimedean methods to study diophantine problems that might be applicable in other arithmetic contexts. Our method at finite places allows us to classify all algebraic relations that hold for infinitely pairs of points in the grand orbit \begin{align*} \mathcal{G}_\alpha = \{\beta \in \mathbb{C}; f^{\circ n}(\beta) = f^{\circ m}(\alpha) \text{ for some } n ,m\in \mathbb{Z}_{\geq 0}\} \end{align*} of $\alpha$ if $|f^{\circ n}(\alpha)|_v \rightarrow \infty$ at a finite place $v$ of good reduction co-prime to $d$ . This is an analogue of the Mordell-Lang conjecture on finite rank groups for polynomial dynamics.

math.NT↗
arXiv2020

A short note on Manin-Mumford

We give a short proof of Manin-Mumford in the multiplicative group based on the pigeon-hole principle and the so-called structure theorem for anomalous subvarieties. The arguments appear to be new and perhaps applicable in other situations.

math.NT↗
arXiv2019

A Manin-Mumford theorem for the maximal compact subgroup of a universal vectorial extension of a product of elliptic curves

We study the intersection of an algebraic variety with the maximal compact subgroup of a universal vectorial extension of a product of elliptic curves. For this intersection we show a Manin-Mumford type statement. This answers some questions posed by Corvaja-Masser-Zannier which arose in connection with their investigation of the intersection of a curve with real analytic subgroups of various algebraic groups. They prove finiteness in the situation of a single elliptic curve. Using Khovanskii's zero-estimates combined with a stratification result of Gabrielov-Vorobjov and recent work of the authors we obtain effective bounds for this intersection that only depend on the degree of the algebraic variety, and the dimension of the group. This seems new even if restricted to the classical Manin-Mumford statement.

math.NT↗
arXiv2019

Rational values of transcendental functions and arithmetic dynamics

We count algebraic points of bounded height and degree on the graphs of certain functions analytic on the unit disk, obtaining a bound which is polynomial in the degree and in the logarithm of the multiplicative height. We combine this work with p-adic methods to obtain a lower bound of the form $cD^{n/4 - \varepsilon}$ on the degree of the splitting field of $P^{\circ n}(z)=P^{\circ n}(α)$, where $P$ is a polynomial of degree $D\geq 2$ over a number field, $P^{\circ n}$ is its $n$-th iterate and $c$ depends effectively on $P, α$ and $\varepsilon$. Our $c$ is positive for each algebraic $α$ for which the set $\{P^{\circ n}(α):n\in\mathbb{N}\}$ is infinite.

math.NT↗
arXiv2018

Unlikely intersections in semi-abelian surfaces

We consider a family, depending on a parameter, of multiplicative extensions of an elliptic curve with complex multiplications. They form a 3-dimensional variety $G$ which admits a dense set of special curves, known as Ribet curves, which strictly contains the torsion curves. We show that an irreducible curve $W$ in $G$ meets this set Zariski-densely only if $W$ lies in a fiber of the family or is a translate of a Ribet curve by a multiplicative section. We further deduce from this result a proof of the Zilber-Pink conjecture (over number fields) for the mixed Shimura variety attached to the threefold $G$, when the parameter space is the universal one.

math.NT↗
arXiv2018

Pfaffian definitions of Weierstrass elliptic functions

We give explicit definitions of the Weierstrass elliptic functions $\wp$ and $ζ$ in terms of pfaffian functions, with complexity independent of the lattice involved. We also give such a definition for a modification of the Weierstrass function $σ$. As immediate applications, we give an explicit uniform zero estimate for $\wp$ and answer a question of Corvaja, Masser and Zannier on additive extensions of elliptic curves.

math.NT↗
arXiv2007

Non Thermal Equilibrium States of Closed Bipartite Systems

We investigate a two-level system in resonant contact with a larger environment. The environment typically is in a canonical state with a given temperature initially. Depending on the precise spectral structure of the environment and the type of coupling between both systems, the smaller part may relax to a canonical state with the same temperature as the environment (i.e. thermal relaxation) or to some other quasi equilibrium state (non thermal relaxation). The type of the (quasi) equilibrium state can be related to the distribution of certain properties of the energy eigenvectors of the total system. We examine these distributions for several abstract and concrete (spin environment) Hamiltonian systems, the significant aspect of these distributions can be related to the relative strength of local and interaction parts of the Hamiltonian.

quant-ph↗
arXiv2005

Control of Local Relaxation Behavior in Closed Bipartite Quantum Systems

We investigate the decoherence of a spin 1/2 subsystem weakly coupled to an environment of many spins 1/2 with and without mutual coupling. The total system is closed, its state is pure and evolves under Schroedinger dynamics. Nevertheless, the considered spin typically reaches a quasi-stationary equilibrium state. Here we show that this state depends strongly on the coupling to the environment on the one hand and on the coupling within the environmental spins on the other. In particular we focus on spin star and spin ring-star geometries to investigate the effect of intra-environmental coupling on the central spin. By changing the spectrum of the environment its effect as a bath on the central spin is changed also and may even be adjustable to some degree. We find that the relaxation behavior is related to the distribution of the energy eigenstates of the total system. For each of these relaxation modes there is a dual mode for which the resulting subsystem approaches an inverted state occupation probability (negative temperature).

quant-ph↗