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Complex geometry is the study of complex manifolds, complex algebraic varieties, complex analytic spaces, and, by extension, of almost complex structures. It is a part of differential geometry, algebraic geometry and analytic geometry.

3 votes

Continuous point map for spherical domains

Here’s an attempt to define such a map which is not an answer but couldn’t fit in a comment. Consider a Riemann mapping $\varphi:\mathbb{H}^2 \to \overset{\circ}{D}$ (which has a continuous extension …
Ian Agol's user avatar
  • 68.9k
9 votes

Complexifications of hyperbolic manifolds

There exist hyperbolic 3-manifolds which cannot embed totally geodesically in complex hyperbolic manifolds, answering this question in the negative. Recently it was shown that complex hyperbolic manif …
Ian Agol's user avatar
  • 68.9k
12 votes
Accepted

Symplectic structure on the square of a 3-manifold

Let $M$ be a 3-manifold fibering over $S^1$, so there exists a fibration $\Sigma \to M \to S^1$. Then $M\times M$ will admit a symplectic structure. There is a symplectic structure on $M\times S^1$, a …
Ian Agol's user avatar
  • 68.9k
31 votes
Accepted

Complex projective manifolds are homeomorphic if homotopy equivalent

For curves this follows from the classification of (2-dimensional topological) surfaces, and for simply-connected surfaces this follows from Freedman's theorem. My former colleagues Anatoly Libgober a …
Ian Agol's user avatar
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6 votes
Accepted

On limits of manifolds

In general, this will be false. Examples are found among solenoidal manifolds, defined by Sullivan. For example, 1-dimensional solenoids. Many of these are obtained by taking the inverse limit of fi …
Ian Agol's user avatar
  • 68.9k
3 votes

Lattices of PU(n,1) with large abelianization

The other answers give fine examples, but I found a reference to the 1981 thesis of Livné which constructs complex hyperbolic lattice which admits a surjective holomorphic map to a Riemann surface. Th …
Ian Agol's user avatar
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2 votes

When is $\mathrm{Aut}(X)\times \mathrm{Aut}(Y)$ of finite index in $\mathrm{Aut}(X\times Y)$?

If $X$ or $Y$ is $\mathbb{D}^n$ (the unit complex ball) or $\mathcal{T}^n$ (Teichmuller space), then $Aut(X\times Y)$ will be finite index in $Aut(X)\times Aut(Y)$. This follows by considering the Kob …
Community's user avatar
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6 votes

Are non-isomorphic covers of riemann surfaces also generally nonisomorphic as riemann surfaces?

There's a remarkable theorem of Margulis that pertains to your question. Let $G$ be a semisimple Lie group (in your case, $PSL_2(\mathbb{R})$), and let $\Gamma$ be an irreducible lattice in $G$. The c …
Mariano Suárez-Álvarez's user avatar
5 votes

Surface of a Ideal Tetrahedron in Hyperbolic Space H3

The surface of the tetrahedron is a 4-punctured sphere, made of 4 ideal triangles. In fact, this is a complete hyperbolic metric, as may be seen by sending $z_1$ to $\infty$ (in fact, we may assume $z …
Ian Agol's user avatar
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3 votes

Injective maps on cohomology and Kahler manifolds

Suppose one has compact symplectic manifolds $(X,\omega), (Y,\sigma)$, and a map $f:X\to Y$ such that $f^\ast\sigma=\omega$ (if $f$ is also a diffeomorphism, then this map is a symplectomorphism, but …
Ian Agol's user avatar
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12 votes
Accepted

A four-dimensional counterexample?

This paper by Hillmann addresses this question. He proves that a surface bundle over a surface which is a complex surface has a holomorphic fibration over the base, for some choice of complex structur …
Ian Agol's user avatar
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6 votes

Kähler structure on cotangent bundle?

In a paper by Goldman, Kapovich, and Leeb, it is pointed out that a fuchsian (surface) group embedded into the isometries of complex hyperbolic space has quotient the tangent bundle to the surface. Si …
Ian Agol's user avatar
  • 68.9k
6 votes

Schwarz Lemma in terms of conformal surfaces or holomorphic curves?

I think the short answer to your question is no, since the notion of a holomorphic map is purely local, whereas the existence of a hyperbolic metric (uniformization) depends on the global structure of …
Ian Agol's user avatar
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5 votes

Rational Hilbert modular surfaces

I don't know the answer to this question, but here's a possible strategy to prove finiteness, following the approach of Zograf, as extended by Long and Reid for congruence arithmetic fuchsian groups o …
Ian Agol's user avatar
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36 votes

What do Weierstrass points look like?

I think another interpretation is in terms of Euclidean geometry instead of hyperbolic geometry. If $\omega$ is a holomorphic 1-form on a Riemann surface $\Sigma$, then $|\omega|$ defines a Euclidean …
Ian Agol's user avatar
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