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Riemannian Geometry is a subfield of Differential Geometry, which specifically studies "Riemannian Manifolds", manifolds with "Riemannian Metrics", which means that they are equipped with continuous inner products.

2 votes
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Relationship between spectrum geometry and almost-isometry

The above comments are still mostly valid with $\epsilon$-isometries: if $(M,g)$ and $(N,g)$ are Riemannian manifolds with diameters less than $D$, then $f:M\to N$, $x\mapsto n_0$ for some $n_0\in N …
Otis Chodosh's user avatar
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9 votes
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Distance between two geodesics originating from separate but nearby points

Let $\sigma(s)$ denote a unit speed minimizing geodesic from $x$ to $y$. Let $l=d(x,y)$ be the length of $\sigma$. Define a vector field $v(s)$ along $\sigma$ by parallel transport. Then set $$ \Gamma …
Otis Chodosh's user avatar
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10 votes
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co-dimension one minimizing verifolds

I think that the phenomena is not stable under perturbation of the metric, i.e., a small perturbation can cause the minimizer to be smooth. First, let me explain how it is not stable under perturba …
Otis Chodosh's user avatar
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3 votes
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The limit of a sequence of embedded minimal disks in $\mathbb{R}^3$

A first answer is (under much weaker hypothesis than you require) Answer 1: If $\Sigma_k$ are a sequence of minimal surfaces with $\partial\Sigma_k \subset B(0,r_k)$ with $r_k\to\infty$ and $ …
Otis Chodosh's user avatar
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5 votes
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A surface on which all regular curves have nowhere vanishing curvature

I'm going to assume that you mean the following property $S \subset \mathbb{R}^3$ has property (*) if for any regular curve $\gamma\subset S$, the curvature vector $\vec{\kappa}$ of $\gamma$ as a …
Otis Chodosh's user avatar
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6 votes
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Singularities in minimal surfaces

On one hand, the answer to the question Is there an analogous of this for minimal surfaces (mean curvature = 0)? I know that minimal surfaces are smooth but, are there examples where they kind of …
Otis Chodosh's user avatar
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6 votes
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A Scalar Curvature Computation in Brendle Marques Neves' Min-Oo Conjecture paper

Willie Wong gives the correct computational method of computing the desired formula. If you happen to believe the general formula for the derivative of the scalar curvature $R$, you can save yourself …
Otis Chodosh's user avatar
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5 votes
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Taylor expansion of the square of the distance function on a Riemannian manifold

The "standard" proof using Jacobi fields can be found in section 1.3 here https://www2.math.upenn.edu/~wziller/math660/TopogonovTheorem-Myer.pdf
Otis Chodosh's user avatar
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3 votes

Computations with the distance function on a Riemannian manifold

UPDATE: I notice that the question leaves the possibility of boundary open. The answer below only works as written if there is no boundary. I'm not sure what happens if there is boundary, but one shou …
Otis Chodosh's user avatar
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12 votes
2 answers
1k views

Converse to Bishop-Gromov Inequality

Is the converse to the Bishop-Gromov Inequality true? In other words, if, for a complete $n$-dimensional Riemannian manifold $M$, there is $k \in \mathbb{R}$, such that defining $V_k(R)$ to be the s …
Otis Chodosh's user avatar
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6 votes
1 answer
388 views

Do manifolds with no Ricci lower bounds for any metric exist?

Is there a smooth (noncompact) manifold $M$ such that for any Riemannian metric $g$ on $M$ there are $p_i$ and unit tangent vectors $v_i \in T_{p_i}M$ such that $Ricc(g)|_{p_i}(v_i,v_i) \leq -i$? This …
Otis Chodosh's user avatar
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5 votes

Convex embedding with a positivity condition

The answer is yes. Even without convexity, a version of Alexandrov's theorem holds true for symmetric functions of the principal curvatures, i.e. if the $k$-th symmetric polynomial of the principal cu …
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1 vote

Normal variation of embedded surfaces

You may end up reading a lot more than just what you wanted to know originally, but I think that Gromov's article Sign and geometric meaning of curvature is an amazing place to look for this sort of i …
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3 votes

Complete stable minimal hypersurface in positively curved manifolds

You can construct a positively curved $(M^n,g)$ for any $n\geq 4$ that admits a stable minimal hypersurface. This is described in Example 1.2 here. (That paper also contains some non-existence results …
Otis Chodosh's user avatar
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4 votes
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On the Geroch's argument

I think that I misunderstood the notation in Question 1. The bold statement is incorrect. Consider the function $\tau(x) = 2x$ on $\mathbb{R}$ and the function $k(x) : = x$ on $\mathbb{R}$. Then $S_t …
Otis Chodosh's user avatar
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