Questions tagged [riemannian-geometry]
For questions about Riemann geometry, which is a branch of differential geometry dealing with Riemannian manifolds.
8,525 questions
2 votes
0 answers
34 views
Reference request: Bounds on laplacian of cutoff functions
I am reading the paper "Liouville Theorems, Volume growth, and Volume comparison for Ricci Shrinkers" by Li Ma. In the proof of Theorem 3, there is a claim: Let $M$ be a complete noncompact ...
0 votes
0 answers
50 views
Are irreducible Hyperkähler manifolds irreducible Riemannian Manifolds.
An irreducible Hyperkähler manifold is an Riemannian manifold of complex dimension $2n$, whose holonomy group with respect to a Kähler metric is $Sp(n)$, the symplectic group. A Riemannian manifold is ...
0 votes
0 answers
61 views
How does Riemann curvature tensor change under conformal transformation [closed]
Show that if $\tilde g=e^{2f}g$ for some function $f,$ then: $$\tilde R^l_{ijk}= R^l_{ijk}-a^l_i g_{jk}-a_{jk}\delta^l_i+a_{ik}\delta^l_j+a^l_jg_{ik}$$ where $a_{ij}$ is given to be: $$a_{ij}=\nabla_i\...
1 vote
1 answer
61 views
Type changing $(1,1)$ to $(2,0)$ tensor
In Petersen's Riemannian Geometry, we have the following passage. The Ricci tensor: For now this is simply an abstract $(1,1)$-tensor: $\mathrm{Ric}(E_i) = \mathrm{Ric}\,_i^j E_j$; thus $$\mathrm{Ric} ...
4 votes
1 answer
58 views
Are the motion equations of an optimal control problem geodesics on a manifold?
Let us consider a Lagrangian system for which the equations of motion come from Hamilton's principle and are such that the control variable $\tau$ equals the equations of motion of a free system, ...
0 votes
0 answers
86 views
Does the hyperbolic space $\mathbb{H}^2$ admit a global, smooth, orthonormal frame? [closed]
Does the hyperbolic space $\mathbb{H}^2$ (hyperboloid model) admit a global, smooth, orthonormal frame? I have tried to compute it explicitly. Let $\Phi: \mathbb{R}^2 \to \mathbb{H}^2\subset \mathbb{R}...
-1 votes
0 answers
80 views
Why is the connection necessary?
Let $M$ be a $n$-dimensional Riemannian manifold, i.e. $M = \cup_{\lambda \in \Lambda}\, (U_{\lambda}, g_{\lambda})$ with each $U_{\lambda}$ being an open ball around the origin of ${\Bbb R}^n$ and $...
3 votes
1 answer
105 views
Conditions to a linear map between tangent spaces being the differential of a isometry
I have the following situation: Suppose that we have two pseudo-Riemannian manifolds M and N, and fixed points $p$ $\in M$, $q \in N$, and a linear isometry between the corresponding tangent spaces ...
0 votes
0 answers
45 views
Reference for the formula for conformal change of sectional curvature
Let $(M, \tilde{g})$ be a Riemannian manifold and let $g:=e^{2u}\tilde{g}$ be a conformal change. I'm trying to find a resource (ideally a book, or a paper where it's mentioned or derived) for the ...
1 vote
0 answers
38 views
Existence and uniqueness of a solution to a Ricci tensor-based boundary value problem [closed]
Let $g$ be a Riemannian metric on a domain $\Omega$ with boundary $\sigma$, and the Ricci curvature tensor is given by $$ R = [\, \partial \Gamma \,] + [\, \Gamma \Gamma \,], $$ where $$ {[\, \partial ...
1 vote
0 answers
27 views
Dualizing Lie derivative with hodge star
I´m trying to find an identity for the operator $\star\mathcal{L}_\nu\star$ acting on k-forms where $\mathcal{L}_\nu$ is the Lie derivative in direction of a vector field $\nu$. Using Cartan's magic ...
3 votes
1 answer
84 views
Is the connection and curvature really derivatives of the metric?
I've often heard people think about the Riemannian connection as the "derivative of the metric", the Riemann tensor as the "Hessian of the metric", and Ricci's tensor as a "...
0 votes
0 answers
39 views
G-invariant metrics on a Tubular neighborhood
Let $G$ be a Lie group acting properly and isometrically on a Riemannian manifold $(M,\mathtt g)$. By the slice theorem, we know that the tubular neighborhood $U=\exp(\nu^\epsilon G(x))$ of an orbit $...
4 votes
1 answer
132 views
The space of complete Riemannian Metrics on a manifold $M$
I was reading this post about the space of Riemannian Metrics, and I would like to know more about the topology of the space of complete Riemannian Metrics on a manifold $M$. Is this space path ...
0 votes
1 answer
162 views
Levi-Civita connection for ${\mathrm{S}}^1$.
Let ${\mathrm{S}}^1$ be a circle with the radius $\frac{1}{2}$, which is a one-dimensional Riemannian manifold. I would like to give the chart on ${\mathrm{S}}^1$ by the affine $x$-real line and the ...