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Gaussian curvature, mean curvature, sectional curvature, scalar curvature, curvature tensors (Riemann, Ricci, Weyl)
12
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2
answers
762
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A Converse to Cartan–Hadamard theorem?
Can we say something about it's curvature?
Is it true that its sectional curvature must be everywhere non-positive (or at least at some point)? … (If not, can we say something about the Ricci or scalar curvature?)
Note that it's clearly not true if we only assume $\exp$ is a diffeomorphism at a single point. …
7
votes
2
answers
391
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Is every metric uniformly close to a metric with negative scalar curvature?
For every $\epsilon >0$ there exist a Riemannian metric $g_{\epsilon}$ with non-positive scalar curvature such that $\|g-g_{\epsilon}\|_{C^0}<\epsilon$? … I ask whether the metrics of non-positive scalar curvature are dense in the space of metrics. …
1
vote
0
answers
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A reference for Poincaré's type inequality for vector fields
$\newcommand{\M}{\mathcal{M}}$
$\newcommand{\TM}{T\mathcal{M}}$
$\newcommand{\Ric}{\operatorname{Ric}}$
$\newcommand{\Volg}{\operatorname{Vol}_g}$
I would like to find a reference for the following c …
1
vote
1
answer
251
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Determining the rate of spread of geodesics when the sectional curvature is zero
($J(t)$ is a Jacobi field, $k$ is the sectional curvature of the relevant plane)
An immediate corollary (2.10 in the book) is:
$\text{(2) } \|J(t) \|=t-\frac 16kt^3+\tilde R(t)$ where $(\frac{\tilde … (Perhaps the values of the sectional curvature in nearby points or its derivatives?) …
14
votes
2
answers
506
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Do curvature differences obstruct a.e orientation-preserving isometries?
We should probably restrict here to manifolds without boundary, since otherwise $M=[0,1],N=\mathbb{R},f(x)=x$ is an example. )
Context:
The point is to see whether curvature differences obstruct existence …