Extension of Matrices with Entries in H^{\infty} on Coverings of Riemann Surfaces of Finite Type

Loewner chains on the universal covering space of a Riemann surface

Let R be a hyperbolic Riemann surface with boundary $\partial R$ and suppose that $γ:[0,T]\to R\cup\partial R$ is a simple curve growing from the boundary of R. By lifting $R_{t}=R\setminus γ(0,t]$ to the universal covering space of R (which we assume is the upper half-plane $\mathbb{H}=\{z\in\mathbb{C}:Im[z]>0\}$) via the covering map $π:\mathbb{H}\to R$, we can define a family of simply-connected domains $D_{t}=π^{-1}(R_{t})$. For each $t\in[0,T]$, suppose that f_{t} is a conformal map of \mathbb{H} onto D_{t} such that f(z,t)=f_{t}(z) is differentiable almost everywhere in (0,T) with respec…

Critical points of random branched coverings of the Riemann sphere

Given a closed Riemann surface $Σ$ equipped with a volume form $ω$, we construct a natural probability measure on the space $\mathcal{M}_d(Σ)$ of degree $d$ branched coverings from $Σ$ to the Riemann sphere $\mathbb{C}\mathbb{P}^1.$ We prove a large deviations principle for the number of critical points in a given open set $U\subset Σ$: given any sequence $ε_d$ of positive numbers, the probability that the number of critical points of a branched covering deviates from $2d\cdot\textrm{Vol}(U)$ more than $ε_d$ is smaller than $\exp(-C_Uε^3_d d)$, for some positive constant $C_U$. In particular, …

Stability of the Bergman kernel on a tower of coverings

We obtain several results about stability of the Bergman kernel on a tower of coverings on complex manifolds. An effective version of Rhodes' result is given for a tower of coverings on a compact Riemann surface of genus greater than or equal to 2. Stability of the Bergman kernel is established for towers of coverings on hyperbolic Riemann surfaces and on complete Kaehler manifolds satisfying certain potential conditions. As a consequence, stability of the Bergman kernel is established for any tower of coverings of Riemann surfaces when the top manifold is simply-connected.

离散周期矩阵和离散全纯积分在黎曼球面分支覆盖中的收敛性

Convergence of discrete period matrices and discrete holomorphic integrals for ramified coverings of the Riemann sphere

研究离散全纯函数在黎曼球面分支覆盖中的收敛性，通过三角剖分和立体投影定义离散调和函数，并证明离散周期矩阵收敛于连续情形，同时给出误差估计和离散全纯积分的收敛结果。

Veech groups of flat structures on Riemann surfaces

In this paper, we construct new examples of Veech groups by extending Schmithusen's method for calculating Veech groups of origamis to Veech groups of unramified finite coverings of regular 2n-gons. We calculate the Veech groups of certain Abelian coverings of regular 2n-gons by using an algebraic method.

A positivity conjecture related to the Riemann zeta function

According to two remarkable theorems of Nyman and Báez-Duarte, the Riemann hypothesis is equivalent to a simply-stated criterion concerning least-squares approximation. In carrying out computations related to this criterion, we have observed a curious phenomenon: for no apparent reason, at least the first billion entries of a certain infinite triangular matrix associated to the Riemann zeta function are all positive. In this article we describe the background leading to this observation, and make a conjecture.

Geometric and analytic problems of the theory of ramified coverings of the sphere

This is a course of lectures given for students of the Regional Mathematical Center of the Novosibirsk State University from October 20 to November 3, 2017. The course is devoted to some geometric problems of ramified coverings of the Riemann sphere. A special attention is payed to compact surfaces of genus one (complex tori). In the first section we give a short introduction to the theory of elliptic functions. Section 2 is devoted to one-parametric families of holomorphic and meromorphic functions. We recall the role of such families on Loewner's equation in solving some problems of the theo…

Uniformizable singular projective structures on Riemann surface orbifolds

This paper is devoted to characterizing complex projective structures defined on Riemann surface orbifolds and giving rise to injective developing maps defined on the monodromy covering of the surface (orbifold) in question. The relevance of these structures stems from several problems involving vector fields with uniform solutions as well as from problems about "simultaneous uniformization" for leaves of foliations by Riemann surfaces. In this paper, we first describe the local structure of the mentioned projective structures showing, in particular, that they are locally bounded. In the case …

Discrete Riemann surfaces based on quadrilateral cellular decompositions

Our aim in this paper is to provide a theory of discrete Riemann surfaces based on quadrilateral cellular decompositions of Riemann surfaces together with their complex structure encoded by complex weights. Previous work, in particular of Mercat, mainly focused on real weights corresponding to quadrilateral cells having orthogonal diagonals. We discuss discrete coverings, discrete exterior calculus, and discrete Abelian integrals. Our presentation includes several new notions and results such as branched coverings of discrete Riemann surfaces, the discrete Riemann-Hurwitz Formula, double poles…

Tower of coverings of quasi-projective varieties

The main goal of this article is to relate asymptotic geometric properties on a tower of coverings of a non-compact Kähler manifold of finite volume with reasonable geometric assumptions to its universal covering. Applicable examples include moduli spaces of hyperbolic punctured Riemann surfaces and Hermitian locally symmetric spaces of finite volume.

Fundamental Domains of Gamma and Zeta Functions

Branched covering Riemann surfaces $(\mathbb{C},f)$ are studied, where $f$ is the Euler Gamma function and the Riemann Zeta function. For both of them fundamental domains are found and the group of covering transformations is revealed. In order to find fundamental domains, pre-images of the real axis are taken and a thorough study of their geometry is performed. The technique of simultaneous continuation, introduced by the authors in previous papers, is used for this purpose. Color visualization of the conformal mapping of the complex plane by these functions is used for a better understanding…

The Riemann Surface of the Logarithm Constructed in a Geometrical Framework

The logarithmic Riemann surface Sigma_{log} is a classical holomorphic 1-manifold. It lives into R^4 and induces a covering space of C - 0 defined by exp. This paper suggests a geometric construction of it, derived as the limit of a sequence of vector fields extending exp suitably to embeddings of C into R^3, which turn to be helicoid surfaces living into C x R. In the limit we obtain a bijective complex exponential on the covering space in question, and thus a well-defined complex logarithm. In addition, the helicoids are diffeomorphic (not bi-holomorphic) copies of Sigma_{log} as smooth real…

Limit constructions over Riemann surfaces and their parameter spaces, and the commensurability group actions

To any compact hyperbolic Riemann surface $X$, we associate a new type of automorphism group -- called its *commensurability automorphism group*, $ComAut(X)$. The members of $ComAut(X)$ arise from closed circuits, starting and ending at $X$, where the edges represent holomorphic covering maps amongst compact connected Riemann surfaces (and the vertices represent the covering surfaces). This group turns out to be the isotropy subgroup, at the point represented by $X$ (in $T_{\infty}$), for the action of the universal commensurability modular group on the universal direct limit of Teichmüller sp…

Families of Line Bundles over Riemann Surfaces, their Sections, and their Degenerations -- A Constructive Approach using Automorphic Forms

In this paper we study the deformation problem of pairs consisting of a Riemann surface and a holomorphic line bundle over that surface, and also sections thereof. We emphasize a constructive approach throughout and work and use covering space techniques. In particular, we also describe the limits of such degenerations as the boundary of Teichmüller space is approached, and review the construction of augmented Teichmüller space in great detail.

Kähler geometry on Hurwitz spaces

We study the Kähler geometry of the classical Hurwitz space $\mathcal{H}^{n,b}$ of simple branched coverings of the Riemann sphere $\mathbb{P}^1$ by compact hyperbolic Riemann surfaces. A generalized Weil-Petersson metric on the Hurwitz space was recently introduced. Deformations of simple branched coverings fit into the more general framework of Horikawa's deformation theory of holomorphic maps, which we equip with distinguished representatives in the presence of hermitian metrics. In the article we will investigate the curvature of the generalized Weil-Petersson Kähler metric on the Hurwitz …

A Uniqueness Property for H^{\infty} on Coverings of Projective Manifolds

Let Y be a regular covering of a complex projective manifold M\hookrightarrow CP^{N} of dimension n\geq 2. Let C be intersection with M of at most n-1 generic hypersurfaces of degree d in CP^{N}. The preimage X of C in Y is a connected submanifold. Let H^{\infty}(Y) and H^{\infty}(X) be the Banach spaces of bounded holomorphic functions on Y and X in the corresponding supremum norms. We prove that the restriction H^{\infty}(Y)\longrightarrow H^{\infty}(X) is an isometry for d large enough. This answers the question posed in [L] by F. Larusson and strengthen his example of the Riemann surface w…

The Profiles of Riemann Surfaces

Riemann surfaces which are set by algebraic, algebroid and inverse functions are considered. A method for describing these Riemann surfaces by graphs is proposed. Each such Riemann surface is assigned to a special type of graph - profile. In terms of graph theory, the necessary and sufficient conditions of profile existence are clarified. The conditions of a one-to-one correspondence between Riemann surfaces and profiles are formulated. In the graph theory terminology the criterion of profiles existence is formulated and proved. The resulting criterion can be used as a criterion of existence o…

非紧致黎曼曲面是等边三角剖分的

Non-compact Riemann surfaces are equilaterally triangulable

本文证明所有开黎曼曲面均可通过粘合可数个等边三角形构造，等价于存在仅在三点分支的全纯覆盖，进而得出任意黎曼曲面是仅在有限点分支的球面覆盖。

穿孔夹层膜的散射：Riemann曲面方法

Scattering by a perforated sandwich membrane: method of Riemann surfaces

研究声波被穿孔夹层膜与硬屏组成的无限平面结构散射的模型问题，提出两种将其归结为2阶向量Riemann-Hilbert问题的求解方法，并利用椭圆曲面与Riemann $θ$-函数实现了精确的Wiener-Hopf矩阵因式分解。