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Complex, contact, Riemannian, pseudo-Riemannian and Finsler geometry, relativity, gauge theory, global analysis.

3 votes

metric scaling for an inequality

You made several mistakes. First, you should apply the result with $R=1$ to the manifold $(M,R^{-2}g)$, so that the unit ball in this scaled metric equals the $R$-size ball in the metric $g$. Secon …
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3 votes

Non-Kahler manifolds and the dd^c-lemma

This does not answer your question, but it seems interesting to point out. A non-example would be any complex threefold diffeomorphic to the six-sphere (if such a manifold exists). To see this, firs …
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5 votes
Accepted

Mukai-Umemura 3-fold and Kaehler-Einstein metrics

[Edited] Such a manifold cannot exist. Indeed the small deformations of the "symmetric" Mukai-Umemura $3$-fold $X$ are described explicitly by Donaldson in this paper, pages 43-44. There he describe …
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12 votes

Two definitions of Calabi-Yau manifolds

It seems worthwile to point out that it is not true that the vanishing of the integral first Chern class of a compact Kahler manifold implies that the canonical bundle is holomorphically trivial. It o …
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7 votes
Accepted

Chern-Einstein metrics on complex Hermitian manifolds

Let me write your equations instead as $$\Theta^{(1)}_{i\bar{j}}=\lambda_1 g_{i\bar{j}},$$ $$\Theta^{(2)}_{i\bar{j}}=\lambda_2 g_{i\bar{j}},$$ where $\lambda_1,\lambda_2$ are real-valued functions. Th …
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6 votes
Accepted

Example of a non-Kähler manifold with varying plurigenera

The first example of this phenomenon was discovered by Iku Nakamura in his 1975 paper Complex parallelisable manifolds and their small deformations, J. Differential Geom. 10 (1975), 85-112. The manif …
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1 vote

Computing the coefficients of the polynomial $\dim H^0(X,L^k)$ in non-smooth case

The answer is contained in the book by W. Fulton "Intersection theory", chapter 18 "Riemann-Roch for singular varieties".
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3 votes
Accepted

"Elliptic" proof that Compact Ricci Solitons are Gradient Ricci Solitons

There is an "elliptic" proof in this paper by Eminenti, La Nave, Mantegazza, see Theorem 3.1. It does still use Perelman's $\mathcal{W}$ entropy (but it does not use the Ricci flow, it just uses a min …
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14 votes

Hsiung on the Complex Structure of $S^6$

I just found this paper by B. Datta (later published in J. Indian Math. Soc. 60 (1994), no. 1-4, 171–190) that explains in details why one key equation in Hsiung's paper is wrong. See the whole discus …
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7 votes
Accepted

Kahler manifolds with constant bisectional curvature

This is theorem 7.9 in the book of Kobayashi-Nomizu "Foundations of Differential Geometry Vol.II". There the authors attribute it to Hawley and Igusa independently. These are probably the first papers …
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12 votes
Accepted

Almost Complex Structures: 'Tame' versus 'Compatible'

If you assume that $M$ is compact and of dimension $4$ then Donaldson has conjectured that if $J$ is $\omega$-tame then $J$ is $\omega'$-compatible for some symplectic form $\omega'$, see Question 2 h …
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1 vote
Accepted

First eigenvalue of $\Delta$ on Kaehler manifold with $Ricci\ge k$.

I am not sure about the history of this result. You can find in Thierry Aubin's book "Some nonlinear problems in Riemannian geometry", Theorem 4.20. He attributes it to his own 1978 paper. The proof …
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7 votes
Accepted

infimum of the Calabi energy in a given Kahler class

If $\Omega$ is a rational Kähler class, so $M$ is projective algebraic, then Donaldson was the first to prove the Chen-Hwang lower bound that you stated. In fact, in this case he proved more, namely t …
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5 votes
Accepted

wedge product of second chern class and kahler form on Calabi-Yau 3-folds.

The calculation in local coordinates is not too hard and it works in any dimension $n$, namely if $c_1(M)=0$ then $\int_M c_2(M)\wedge\omega^{n-2}\geq 0$ for any Kahler metric $\omega$. Of course you …
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0 votes

Navier-Stokes equations in Riemannian geometry

For what it's worth, the Navier-Stokes equation on manifolds is also mentioned in this recent paper http://arxiv.org/pdf/1107.2698, see (1.16) there, in connection with another flow for vector fields …
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