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Riemann surfaces(Riemannian surfaces) is one dimensional complex manifold. For questions about classical examples in complex analysis, complex geometry, surface topology.

20 votes
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Teichmuller Theory introduction

The primer on mapping class groups, by Farb and Margalit.
13 votes
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Hyperbolicity on Riemann Surfaces

NEW ANSWER: As there has been much confusion on this point (some of it mine...): Definition: A Riemannian 2-manifold $S$ is of hyperbolic type if the universal cover of $S$ is conformally equiva …
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12 votes

Is a positive degree self map on a Riemann surface homotopic to a holomorphic self map?

The answer is "yes" if $S$ is the Riemann sphere. This is because a map $f$ of degree $d$ from the sphere to itself is homotopic to $z \mapsto z^d$. The answer is "basically no" if $S$ has genus two …
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11 votes
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What is the minimal genus of a surface acted on by the symmetric group $S_n$?

I don't have a precise answer, but the genus of $S$ has to grow like $n!$. To see this, note that when $n$ is large enough, $S$ cannot be the sphere or torus. So $S$ admits hyperbolic metrics. By Ni …
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9 votes

Explicit description of the group of deck transformations acting on the universal cover of a...

Looking at the link you give, it seems that you want an explicit representation of $\pi_1 = \pi_1(S)$, the fundamental group of the genus two surface, into $\mathrm{PSL}(2, \mathbb{C})$ so that the up …
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7 votes

Quotient of the hyperbolic plane with respect to commutator group of $\pi_1(\Sigma_g)$

$\newcommand{\ZZ}{\mathbb{Z}}\newcommand{\RR}{\mathbb{R}}$Let $S = \Sigma_2$ be the genus two surface. In this case, $\ZZ^4$ is the deck group of the desired covering. Consider $\ZZ^4$ inside of $\R …
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7 votes
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Reference for Teichmuller spaces of punctured surfaces

Fred Gardiner's book Teichmüller theory and quadratic differentials is a good reference. He (a) deals with the punctured case (called finite analytical type: see the first page of Chapter 2), (b) cov …
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6 votes
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Intersection of closed geodesics in hyperbolic surface

The answer to (1) is yes. Take $P$ a hyperbolic surface with one geodesic boundary, called $\delta$, and two punctures. Form $S$, a sphere with four punctures, by doubling $P$ across $\delta$. No …
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6 votes
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Moduli, Teichmüller spaces and mapping class group of a sphere with four punctures

In your description of moduli space you say: I can use a Moebius transformation to send three of the punctures at those location whilst the fourth puncture is free to move. That assumes that …
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6 votes

Torsion elements in the mapping class group

Collecting some of the answers above, and editing a bit: What can one say about its torsion elements? $\newcommand{\Mod}{\mathrm{Mod}}$As with lattices in Lie groups, and in word-hyperbolic groups, …
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6 votes
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Homotopy classes of homeomorphism vs. Homotopy classes of a biholomorphism

No, certainly not. Biholomorphic maps are very rare and very rigid. Generically, given Riemann surfaces $X$ and $Y$, there will be no biholomorphic maps between them. Yes. You will want to read u …
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4 votes

Flat regions on surfaces of genus greater than 1

Let $S$ be the underlying surface and call the image of the dotted lines $\gamma$. If we cut $S$ along $\gamma$ then $S$ falls apart into two components $X$ and $Y$ (both tori with a single boundary …
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4 votes

Universal covers of punctured hyperbolic surfaces

For the thrice-punctured sphere, there is a generating set where both generators are parabolic. For the once-punctured torus only the commutator (and its conjugates) is parabolic. Hence any element …
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4 votes
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Is action of MCG on the curve complex computable for closed surfaces? [Yes: Birman Exact Seq...

You write "it appears that the action of the MCG on the curve complex is incomputable for closed surfaces." This is not correct. Geva Yashfe points out one approach in the comments. Here is another, …
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4 votes

Uniformizations of the bordered/punctured Riemann surfaces

In the closed or bounded case, there is a uniformization of a Riemann surface by a fuchsian group. In the closed case this is the content of the uniformization theorem. The bounded case follows from …
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