arXiv · 2008.12189
We give an elementary and self-contained proof of the uniformization theorem for non-compact simply-connected Riemann surfaces.
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Cipriana Anghel, Rares Stan. 2021-09-03. Uniformization of Riemann surfaces revisited. https://arxiv.org/abs/2008.12189
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We consider the Hill equation $f''-(\sum_{i=-\mathbf{l}}^{\mathbf{k}}b_{i}e^{iz})f=0$ ($†$), where $\mathbf{k}\geq 1$ and $\mathbf{l}\geq 0$ are integers and $b_{-\mathbf{l}}$, $\cdots$, $b_{\mathbf{k}}$ are constants such that $b_{\mathbf{k}}\not=0$. We point out that there is a full correspondence between the class of non-oscillatory solutions such that $λ(f)<\infty$ of equation ($†$) and the class of Liouvillian solutions of equation $x^2u''-(\sum_{i=-\mathbf{l}}^{\mathbf{k}}b_{i}x^{i})u=0$ ($‡$). Then this paper has twofold purposes. First, parallel to Kovacic's algorithms to find the Liouvillian solutions of equation ($‡$), we develop the Tumura--Clunie method to find the non-oscillatory solutions of a higher order version of the Hill equation. Second, for the particular Hill equation $f''-(b_{\mathbf{k}}e^{\mathbf{k}z}+b_{\mathbf{s}}e^{\mathbf{s}z}+b_0)f=0$, where $\mathbf{k}>\mathbf{s}\geq 1$ are integers and $b_{\mathbf{k}}b_{\mathbf{s}}\not=0$, we use the Tumura--Clunie method to determine the non-oscillatory solution $f$ with an additional zero property.
We study holomorphic isometric maps $F=(F_1,\cdots,F_m)$ from the complex unit ball $\mathbb{B}^n$, $n\geq2$, to a product of irreducible bounded symmetric domains $Ω_1\times\cdots\timesΩ_m,$ equipped with positive constant multiples of their canonical Kähler--Einstein metrics. We prove that every nonconstant component $F_i$ is itself a holomorphic isometry up to a constant factor. This proves the componentwise rigidity conjecture formulated by Yuan in 2019.
By a result of F. R. Keogh in 1959, we have the inequality $L(r,f)/M(r,f)\le 2π+4\log[(1+r)/(1-r)]$ for a starlike function $f$ on the unit disk, where $L(r,f)$ and $M(r,f)$ denote the length of the curve $θ\mapsto f(re^{iθ})$ and the maximum value of $|f(z)|$ on the circle $|z|=r$ for $0<r<1.$ E. Crane and D. Markose in their 2005 paper showed that the constant $4$ is best possible. D. K. Thomas obtained in 1968 the inequality $L(r,f)/\sqrt{A(r,f)}\le 2\sqrtπ(1+\log[(1+r)/(1-r)])$ for a starlike function $f$, where $A(r,f)$ is the area of the image of the disk $|z|<r$ under the mapping $f.$ In this paper, we extend these results to the case of $λ$-spirallike functions for a given $λ$ with $-π/2<λ<π/2.$