A branch of differential geometry dealing with Riemannian manifolds. *Riemannian manifolds* are smooth manifolds with an inner product smoothly attached to the tangent space of each point. Usually, Riemannian geometry focuses on the notions of distance, curvature, and shape. Consider using this tag ...

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Is the tangent-cotangent isomorphism orientation preserving?

Consider $(M,g)$ a Riemannian manifold. Let's define $\varphi : TM\rightarrow T^{\ast}M$ by $\varphi(p,v):=(p,g(v,.))$, for $p\in M$ and $v\in T_{p}M$. Here, $TM$ stands for the tangent bundle and ...
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What's wrong in this prop about volume form if we drop “oriented”?

I was studying Prop 15.29 from Lee's Introduction to Smooth Manifold and I asked myself what's wrong with this proof if we drop the oriented assumption. I know that I'd came up with a non zero ...
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Does a Riemannian metric allow definition of a tangent vector's length?

In Euclidean spaces, we define the Euclidean norm of a vector $\vec{x} = (x_1,x_2,...x_n)$ as $\|\vec{x}\|:=\sqrt{x_1^2+x_2^2+ \cdots +x_n^2 }$ Does the metric tensor field of a Riemannian manifold ...
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32 views

How can I measure the length of a curve using a Riemannian metric?

On page 35 in his book Riemannian Geometry, Manfredo do Carmo states the following: Giving a surface $S \subset \Bbb{R}^{3}$, we have a natural way of measuring the lengths of vectors tangent to ...
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Is $M \times (0,\infty)$ a manifold of bounded geometry?

If $M$ is a compact Riemannian manifold, is $M \times (0,\infty)$ a manifold of bounded geometry? I think it is, since $M$ is compact and $(0,\infty)$ is simply flat.
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Completeness implies geodesic completeness, a more conceptual way?

We know from Riemannian geometry that for Riemannian manifolds, completeness and geodesic completeness are equivalent, which is usually a consequence of Hopf-Rinow theorem. However, I'm considering a ...
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23 views

Definiton of a riemanian metric (smoothness)

In Ana Cannas de silva's book Lectures on Symplectic geometry he defines a positive inner product to be smooth when for any vector field $v$ the function $x \mapsto g_x(v_x, v_x)$ is smooth. Some ...
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Angles on geodesic triangle of complete Riemannian manifold

I meet a problem on my course Riemannian Geometry, It is Let M be a complete and simply connected Riemannian manifold with all sectional curvatures in the interval $[-k_0^2, -k_1^2 ]$ with $0 ...
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57 views

Every possible choice of Christoffel symbols generate a valid connection

Does every possible choice of Christoffel symbols generate a valid connection? Or is there some restriction on them?
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38 views

In the standard definition of an affine connection, what does $\nabla$ stand for?

I am very confused about what $\nabla$ signifies when used to describe affine connections. In his book Riemannian Geometry, Manfredo do Carmo defines an affine connection as follows. Let ...
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Breaking down what the definition of an affine connection says

In his book Riemannian Geometry, Manfredo do Carmo defines an affine connection as follows: Let $\mathcal{X}(M)$ denote the set of all vector fields of class $C^{\infty}$ on $M$. Let ...
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Laplace-de Rham operator

Consider an operator $\partial = (-1)^k \star^{-1}\,d\star: \Omega^k(\mathbb{R}^n) \to \Omega^{k-1}(\mathbb{R}^n)$. Note that we equivalently can write $\partial = (-1)^{nk + n + 1} \star\,d\star$. ...
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32 views

on isometric group

Let $G_n$ be a Lie group, $g$ denotes the left invariant Riemannian metric on $G$. I want to ask for help that how to prove this conclusion: if all principal Ricci curvature of $(G_n, g)$ are ...
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51 views

Sufficient condition for $M$ to have constant curvature

I decided to keep my original question. However, I'm having trouble only in a part of it (check NOTE) Let's consider a Riemannian manifold $(M,g)$, with the Levi-Civita connection $\nabla$. I would ...
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34 views

Boundary points of a manifold

I'm reading about Riemannian Geometry and my question is regarding Manifolds with Boundary. I want to show a point of a manifold with boundary is either an interior point or a boundary point, so no ...
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Order of Riemann tensor indexes and the Ricci Identity

I have seen the Ricci identity written variously as $R_{ijk}{}^l x^k = (\nabla_i\nabla_j- \nabla_j\nabla_i) x^l$ $R_{ij}{}^l{}_k x^k = (\nabla_i\nabla_j- \nabla_j\nabla_i) x^l$ $R^l{}_{kij} x^k = ...
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When does a pseudo-Riemannian manifold have an always positive norm Killing field?

When does a pseudo-Riemannian manifold have an always positive norm Killing field? (you may assume that the isometry group is of the form $SO(1,n)$ if necessary) In the context of general ...
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44 views

The level set of Lipschitz functions

Suppose $u$: $R^N\to R$ is lipschitz, then do we have a.e. level set of $u$ has Lipschitz boundary? Is this anything to do with Sard theorem? Sard theorem states that a.e. Level set of smooth ...
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63 views

At what conditions a compact metric space of covering dimension $n$ (on $\mathbb R^n$) is an n-manifold?

In the discussion to the MSE post an answer of @MatthewPancia with correction in a comment of @JasonDeVito would state: Every compact metric space of covering dimension $n$ can be embedded ...
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2answers
55 views

Raising and Lowering Through Differentiation

I'm calculating the Christoffel symbols of the second kind which is of course defined as multiplying the symbol of the first kind multiplied by the contravariant metric. I was thinking of how to make ...
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A question about sum of angles in a non-positive curvature Riemannian manifold

Suppose on a non-positive curvature Riemannian manifold,we have a geodesic triangle $\triangle abc$ ,and counterpart edges donates $\alpha,\beta,\gamma$. If now I get $$ a^2 \geqq b^2+c^2-2bc ...
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Ricci curvature version of Cartan-Hadamard theorem?

Is the following assertion true : If $M$ is a simply-connected manifold with $\operatorname{Ric}<0$ (or $\operatorname{Ric}\leq -k$ for $k$ positive) then $M$ is diffeomorphic to $\mathbb{R}^n$? ...
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Is Relativity a specific instance of Riemannian geometry?

If I am a mathematician and do not anything about Special/General Relativity, then should I study Riemannian geometry to learn Relativity? Is Relativity just an instance/example of some particular ...
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Explicit example of a compact manifold of dimension $>2$ with strictly negative sectional curvature

I am looking for examples of compact manifold of dimension $>2$ with strictly negative sectional curvature (for dimension 2 it is well-known). Can anybody please help?
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Symmetry of Killing Vectors in Covariant Derivative

Several times, I've seen statements along the lines of "$\nabla_X Y=\nabla_Y X$ because $X$ is a Killing vector field." One example I found on Stack Exchange is here. I have yet to understand why ...
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87 views

Smoothly homotoping a sphere in $\mathbb{R}^3$

Start with the standard sphere $S^2$ and consider another (diffeomorphic) sphere $S$ such that there is a family of deformations of $S^2$ in $\mathbb{R}^3$ that ends in $S$. If $S$ is positively ...
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26 views

Conformal transformation of the divergence

Let $f$ be a smooth function on a $n$-dimensional Riemannian mainfold $(M, g)$, so that $\tilde{g} = e^{2f} g$ is a conformal transformation of $g$. I'm trying to show that the divergence operator ...
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51 views

Riemannian curvature tensor of product manifolds

Let $(M_{1},g_{1})$ and $(M_{2},g_{2})$ be two Riemannian manifolds. Let $% R_{1}$ and $R_{2}$ be the (1,3)-type Riemannian curvature tensors of $M_{1}$ and $M_{2}$, respectively. Finally, let $R$ be ...
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73 views

Cohomology in Differential Geometry

Below is a communicative diagram: $$\begin{array}[c]{ccc} ...
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40 views

What properties do isospectral Riemannian manifolds share?

I'm studying the Laplacian on (compact) Riemannian manifolds, and it turns out that if the Laplacian operators of two such spaces share their spectrum (the spaces are then called isospectral), then ...
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54 views

Jacobi field and the metric

I'm reading about Jacobi fields lately, and have noticed some features of it (and it's derivative) with respect to the metric. Thinking about that, I had an non-based, purely intuitive thought that ...
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Closed geodesic loop on compact manifold

Let $M$ be a compact manifold (hence complete). Let $p$ be any point on $M$. Is it true that we can always find a geodesic loop based at $p$? If $M$ is non-simply connected it is true as each ...
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Explicit formula for the (n-2)th derivative of the Jacobi equation

The $n-2$ order derivative of the Jacobi equation is given by: $$\frac{D^n}{dt^n} V_i+\sum\limits_{l=0}^{n-2} \binom{n}{k} (\nabla_{\gamma '}^{(n-2-l)}R)(\gamma ' ,\nabla_{\gamma '}^{(l)} V_i)\gamma ...
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49 views

Surfaces (with boundary) in $\mathbb{R}^3$ conformal to the cylinder

Consider the usual cylinder $S^1 \times [0, 1]$ embedded in $\mathbb{R}^3$. I am interested in knowing what are the surfaces in $\mathbb{R}^3$ that are conformal to this cylinder. If this were a ...
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How to show that geodesics exist for all of time in a compact manifold?

Let $M$ be a compact manifold and the tangent bundle $TM$ have a Riemannian metric $g$ so that it is isomorphic to the cotangent bundle $T^*M$. Consider the pull-back of the canonical symplectic form ...
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Covariant derivative of vector field along itself: $\nabla_X X$

Consider a vector field $X$ on a smooth pseudo-Riemannian manifold $M$. Let $\nabla$ denote the Levi-Civita connection of $M$. Under which conditions can something interesting be said about the ...
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Show that a parallel field has constant length.

Show that a parallel field has constant length (Riemannian-geometry). It is true for all connections?
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Find an example of n-dimensional differentiable manifold

Find an example of $n$-dimensional differentiable manifold whose points are not points of the variety $\mathbb{R}^{n}$
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Metric in normal coordinate

Using Gauss’s lemma we can write the metric in normal co-ordinate as $g(r, θ) = dr^2 + r^2h_{ij}(r, θ)dθ^i ⊗ dθ^j$ (where metric on $S^{n-1}$ is $\tilde {g}=dθ^i ⊗ dθ^i$). Now as $r \rightarrow 0$, ...
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Showing a property of a curvature tensor in $S^2$

Consider $S^2 \subset \mathbb{R}^3$. I need to show that if $$R_{ijkl} = -g(R(\partial_i,\partial_j)\partial_k,\partial_l)$$ is a curvature tensor in $S^2$ and $g$ is a metric also in $S^2$, then ...
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27 views

Variation of geodesic and Jacobi field

I was reading on Jacobi field of a geodesic, and noticed that given a geodesic $\gamma$ it is defined using the term of variation or family of geodesics $\gamma_s$ but never mentioned how to create ...
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45 views

Are there “interesting” examples of complete finite-volume non-compact Riemannian manifolds that are not non-positively curved?

Moreover, it would be good that, if $M$ is such an example, its universal cover $\tilde M$ is "highly" symmetric, i.e. the group G of isometries of $\tilde M$ is "big" (for example, transitive, or a ...
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42 views

Geodesic loops in Riemann homogeneous spaces

Let M be a Riemannian homogeneous space, i.e. the isometry group acts transitively. Prove: any geodesic loop (with possible angle at the starting point) is a closed geodesic (smooth at the starting ...
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74 views

Sectional curvature of product metric?

If $M$ and $N$ are Riemannian manifolds, can we relate the sectional curvature of the product Riemannian manifold $M \times N$ to those of $M$ and $N$? If both $M$ and $N$ have non-negative (or ...
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Riemann manifolds in relation to other classes of differentiable manifolds

I am trying to get an overview over the different categories of manifolds. In particular i have the following chain of inclusions: Riemann surfaces $\subset$ complex manifolds $\subset$ orientable ...
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Curvature of De Sitter's space: where does the sign comes?

Consider $\Bbb L^3 = (\Bbb R^3, {\rm d}s^2)$, where: $${\rm d}s^2 = {\rm d}x^2 + {\rm d}y^2 - {\rm d}z^2.$$ We have both the hyperbolic space: $$\Bbb H^2(-1) = \{(x,y,z) \in \Bbb L^3 \mid ...
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Out of plane cross section evolution of surfaces based on local geometry information

With this question I would like to kindly ask for feedback or general pointers to even remotely related works in regards to a challenge I face. Given a smooth surface $S$ $:\mathbb{R}^2\rightarrow ...
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55 views

“Rigid” Riemannian metrics

What do we mean when we say that a Riemannian metric $g$ is rigid? For example, the Eguchi-Hanson metric is rigid as an Einstein metric. Any help is appreciated!
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Resource for learning about the Laplacian on Riemannian manifolds

Does anyone have any recommendations for, as the title suggests, a book from which to learn about the Laplacian on Riemanian manifolds, or even just on smooth manifolds? I found this presentation, ...
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Symmetries of Weyl Tensor

We know that the Riemannian curvature $(0,4)-$tensor may be decomposed as $$Rm=W\;+\;A *g$$ where $*$ is the Kulkarni-Nomizu product, and $A$ the Schouten tensor. I am studying the proof of a theorem ...