All Questions
Tagged with reference-request dg.differential-geometry
800 questions
2
votes
3
answers
613
views
Manifolds with special holonomy especially $G_2$
I am interested in learning about $G_2$ manifolds and am aware that one of the canonical references is Joyce's Compact Manifolds with Special Holonomy. I am certain that my background is, at this ...
- 21
2
votes
0
answers
346
views
What information is encoded in discriminant varieties?
I'm looking for Web-accessible references that survey the connnections among the following constructs:
discriminant varieties
Vandermonde matrix/determinant/polynomial
moment curves for the n-...
- 10.5k
8
votes
0
answers
480
views
Connections and curvature in commutative algebra
Since on any commutative algebra $R$ over ring $S$ we have module of Kahler differentials $(\Omega_{R/S},d)$ which extends to the algebraic de-Rham complex $(\Omega^\bullet,d),$ it is natural to ...
- 1,615
2
votes
0
answers
127
views
Functional inequality under mean curvature flow
Let $\Sigma$ be a hypersurface in $\mathbb R^n$ and $\Sigma_t$ be a variation of $\Sigma$ under the mean curvature flow under an extra condition that ${\rm vol}_{n-1}(\Sigma)={\rm vol}_{n-1}(\Sigma_t)$...
- 143
29
votes
5
answers
3k
views
Most manifolds are hyperbolic?
I heard the claim as in the title for a long time, but can not find the precise reference for this claim, what's the reference with proof for this claim? Thanks for the help.
To be more precise, is ...
- 799
4
votes
1
answer
565
views
Riccati equation and principal curvatures
Let $\Omega$ be an open subset of a Riemannian manifold $M$. Assume that $\Sigma:=\partial \Omega$ is $C^2$.
Let $U$ be a neighborhood of $\Omega$ such that $\exp_p(t\nu(p))$ is diffieomorphism, ...
- 143
8
votes
1
answer
682
views
Geometry of convex sets in Riemannian manifolds
Let $M$ be a smooth Riemannian manifold without boundary. Let $X\subset M$ be a closed subset which is a smooth submanifold with boundary, $\dim X=\dim M$. Assume that $X$ is locally convex, i.e. any ...
- 21.8k
5
votes
0
answers
96
views
Is every space group the symmetry group of some triply periodic minimal surface?
I know that there are a lot of TPMS with different symmetry groups. It seems like every space group is the symmetry group of some TPMS. But I can not find a reference that confirms this for all the ...
- 2,581
8
votes
4
answers
710
views
Torsion of submanifolds
Studying curves in the Euclidean three dimensional space, one usually defines the curvature and the torsion of a curve. If I am not missunderstanding the thing, I guess that a curve has zero torision ...
- 2,384
2
votes
0
answers
138
views
Geometric flow of the total tension functional
I apologize if this question is silly or confusing, I am completely new to this subject.
Let $(M,g)$ be a Riemannian manifold. Denote by $\nabla$ the Levi-Civita connection of $(M,g)$. Now, let $S^{n}...
- 395
4
votes
1
answer
347
views
Some questions on a paper of Wilking
I am currently trying to understand Wilking's paper "A Lie algebraic approach to Ricci flow invariant curvature conditions and Harnack inequalities" (DOI: 10.1515/crelle.2012.018, arXiv:1011....
- 81
5
votes
0
answers
391
views
Gage-Grayson-Hamilton curve-shortening flow, at an angle
The Gage-Grayson-Hamilton curve-shortening flows along the normal to the curve:
&...
- 151k
3
votes
1
answer
239
views
What is the curved version of the Tits fibration for $G_2$?
Let
$\require{AMScd}$
\begin{CD}
G_2/(P_1\cap P_2) @= G_2/(P_1\cap P_2)=:\mathbb{I}\\
@V \lambda V V @VV \pi V\\
\mathbb{Q}_5:=G_2/P_1 && G_2/P_2=:\mathbb{N}_5
\end{CD}
be the Tits ...
- 2,527
3
votes
0
answers
203
views
Reference: Differential geometry on surfaces that are graphs of 2D-fluid-equations and Point Vortices
In "Pressure Field, Vorticity Field, and Coherent Structures in
Two-Dimensional Incompressible Turbulent Flows" Larchev$\hat{e}$que computes the Gaussian curvature of the surface of the streamfunction ...
- 5,474
6
votes
1
answer
1k
views
Geometry of the complex quadric
The complex orthogonal group $O(n+1, \mathbb{C})$ acts transitively on the complex quadric
$$
Q_{n-1} := \{[z_0:z_1: \cdots :z_n] : z_0^2 + \cdots z_n^2 = 0 \} \subset \mathbb{CP}^n.
$$
What is ...
- 13.5k
2
votes
2
answers
2k
views
Commuting of exterior derivative and contraction (vector-valued forms)
$\newcommand{\sig}{\sigma}$
$\newcommand{\tr}{\operatorname{tr}_{\eta}}$
$\newcommand{\al}{\alpha}$
$\newcommand{\be}{\beta}$
$\newcommand{\til}{\tilde}$
Let $E$ be a smooth vector bundle over a ...
- 6,741
10
votes
2
answers
2k
views
References for differential cohomology and differential characters
I am interested in learning differential cohomology and differential characters, and am currently studying these lecture notes on the subject. I sometimes feel it would be great if I could keep some ...
4
votes
1
answer
234
views
A trivialization of an almost complex structure
Recently, I have been studying the Carleman Similiarity Principle, which is used to study the regularity and unique continuation of J-holomorphic curves.
Roughly, one takes a solution $ u $ of a ...
- 337
3
votes
2
answers
1k
views
Reference for homogeneous spaces
I am a graduate student of differential geometry.
I would like to get an overview over the way, how results are usually obtained for homogeneous spaces by Lie algebraic methods. By definition a ...
- 79
2
votes
3
answers
397
views
Reference request for structure equations
Let $(M,g)$ be a Riemannian manifold and let $\lbrace e_1,...,e_n\rbrace$ be a locally frame field on $M$ and $\omega _1 ,...,\omega _n$ be the dual $1$-forms of it. If $\omega _{ij}$ be the ...
- 601
122
votes
7
answers
15k
views
Topology and the 2016 Nobel Prize in Physics
I was very happy to learn that the work which led to the award of the 2016 Nobel Prize in Physics (shared between David J. Thouless, F. Duncan M. Haldane and J. Michael Kosterlitz) uses Topology. In ...
3
votes
0
answers
177
views
Morse-Bott functions without critical manifolds of index 1 and n-1
I am now reading the article of M.F.Atiyah "Convexity and commuting hamiltonians" and I can't understand lemma 2.1. which says that if $\varphi \colon M \to \mathbb R$ is a Morse-Bott function without ...
- 2,305
2
votes
1
answer
214
views
What is the space parametrising the curved sub-Cartan geometries of a flat Cartan geometry?
I'm basically wondering how to make "curved" the first column of the diagram
$\require{AMScd}$
\begin{CD}
P_1 @>\textrm{inclusion} >> G\\
@V \omega_0 V P_1\cap P_2 V @V\omega V P_2 V\\...
- 2,527
5
votes
1
answer
328
views
Is a space with p-norm a Finsler manifold?
Suppose $\mathbb{R}^n$ is equipped with the p-norm $\left\Vert x \right\Vert_p$. Let $x\in \mathbb{R}^n$ and let $y$ be in a neighborhood of $x$. The distance between $x$ and $y$ can be defined as $\...
- 51
3
votes
1
answer
81
views
Estimating the Size of an Approximating Polyline
let $\gamma(s) = \left(x(s),y(s)\right), s\in[0,1]; \gamma'(s) = 1$ be a length-parameterized curve in the plane, with finite and strictly positive curvature.
Questions:
is it possible to estimate ...
- 13.2k
19
votes
1
answer
1k
views
Ehresmann's theorem over the $p$-adics
I am looking for a version of Ehresmann's theorem for analytic manifolds over the $p$-adic numbers $\mathbb{Q}_p$ or, more generally, local fields. I follow the conventions from Serre's book "Lie ...
- 21.3k
3
votes
1
answer
496
views
Ricci flow preserves holonomy
Could someone please give me a reference where I can find a complete proof of the result Ricci flow preserves holonomy? Is there any way to prove that Ricci flow preserves Kahler condition without ...
- 789
3
votes
1
answer
333
views
Elementary question: Curvature change under Complexified Gauge Transformation
Forgive me for this elementary question.
Let $E$ be a holomorphic vector bundle over a Riemann surface $M$ equipped with a Hermitian metric. Let $\nabla$ be the compatible connection on $E$ amd $g$ ...
- 297
2
votes
2
answers
332
views
Heat kernel upper bounds on a complete Riemannian manifold
Let $M$ be a complete Riemannian manifold, and $p(t, x, y)$ denotes its heat kernel. I am trying to find sufficient conditions for when the following holds:
$$ p(t, x, y) \leq Ct^{-n/2}, \forall x, y, ...
- 21
4
votes
3
answers
669
views
Gaussian bounds on Dirichlet heat kernel
Let $(M, g)$ be a compact Riemannian manifold and let $p(t, x , y)$ be the heat kernel of $M$. Then there exist constants $c, C > 0
$ such that $$\frac{c}{t^{n/2}}
e^{-\frac{1}{4t}d(x, y)^2} \leq ...
- 81
4
votes
0
answers
294
views
Various definitions of the odd Chern character form
I am asking this question from my possibly defected memory, so the things below may not be accurate.
I want to know how many different definitions of the odd Chern character form using differential ...
- 1,173
1
vote
1
answer
211
views
Curvature of plane curves on a surface
Let $S$ be a surface and $\gamma$ a curve on $S\subseteq \mathbb{R}^3$ obtained cutting $S$ with a plane. I wuold an upper bound for the curvature of $\gamma$. Are there papers for this topic?
- 1,252
4
votes
0
answers
237
views
Contact manifolds and pseudodifferential operators
By way of background, I am currently trying to understand the theory of pseudodifferential operators in the context of contact geometry. I have some knowledge of pseudodifferential operators on ...
- 41
17
votes
0
answers
1k
views
Jets of sections of vector bundles expressed by symmetrized iterated covariant derivatives - who did it first?
The (non-unique) bundle isomorphism between the bundle $J^r E$ of $r$-th order jets of sections of a vector bundle $\pi:E\rightarrow M$ and the direct sum $$\bigoplus^r_{k=0}\vee^kT^*M\otimes E\...
- 7,817
3
votes
0
answers
172
views
question about currents
I have a question in the field of currents:
Let M be an n-dimensional smooth manifold, and let T be a k-current (induced by a k dimensional sub-manifold), I would like to approximate it by a series of ...
- 31
2
votes
0
answers
145
views
Semistability of a sheaf on nodal curve
Suppose $X$ is a projective, connected, nodal curve (can be reducible) over an algebraically closed field $k$ of arbitrary characteristic. Let $F$ be a pure sheaf on $X$ and denote by $\pi^{*}(F)$ its ...
- 2,323
2
votes
0
answers
67
views
On two functions with isodirectional gradients
Let $U\subset \mathbb{R}^n$ be open and $f,g:U \to \mathbb{R}$ be two $C^1$ functions whose gradients are always in the same direction, i.e. $\forall i,j \in \left\{1,...,n\right\}$
\begin{equation}
(\...
- 1,461
4
votes
0
answers
172
views
Donnelly-Fefferman growth of eigenfunctions
Let $(M, g)$ be a compact Riemannian manifold, and let $\lambda^2$, $\varphi_\lambda$ represent eigenvalues and eigenfunctions respectively of the Laplacian $\Delta$, that is, $-\Delta \varphi_\lambda ...
- 41
8
votes
2
answers
377
views
Surfaces contained in a ball
In this Paper there is a proof that a closed plane curve of length
$L$ and curvature bounded by $K$ can be contained inside a circle of radius
$L/4 - (\pi - 2)/2K$. Are there similar results for ...
- 1,252
13
votes
4
answers
3k
views
General Relativity and Differential Geometry intuitions of Second Bianchi Identity
In General Relativity, one uses the Riemann Tensor in its coordinate form $R_{abcd}$, and proves the Second Bianchi Identity-
$R_{abcd;e} + R_{abde;c} + R_{abec;d} = 0$
It is said that ...
- 3,574
9
votes
1
answer
630
views
$C^{k,\alpha}$ diffeomorphisms and vector fields
This feels like something I should know, but I have a hard time finding a definite reference.
Let $M$ be a compact (Riemannian) manifold, $k\ge 1$ be an integer and $\alpha\in(0,1)$. When v is a $C^k$...
- 14.4k
6
votes
1
answer
417
views
"structure group" for fibration
Regarding "fibration" as a homotopy analogue of "fiber bundle",I want to see parallel notions of "structure group" and "fiber change" in "fibration".
Does it make sense to talk about "structure group"...
- 71
3
votes
0
answers
269
views
covariant derivative of manifold-valued function and logarithm map
Let $M$ be a Riemannian manifold and $f\colon \Omega\subset \mathbb{R}^d\rightarrow M$ a smooth, i.e. $C^\infty$, function. For any $p\in M$ let $T_pM$ be the tangent space at $p$ and $\log_p\colon U\...
- 2,286
1
vote
1
answer
64
views
Unbounded convex domains in 2D
Let $\gamma$ be a smooth planar curve. Assume that $\gamma$ divides the plane into two domains and, it addition, that one of these domains is unbounded and convex. What can be said about the behavior ...
- 175
12
votes
1
answer
3k
views
how to define the injectivity radius of manifolds with boundary?
For manifolds without boundary one defines the injectivity radius as the maximal radius where the exponential map is a diffeomorphism. One can then show that the injectivity radius is the maximum ...
- 687
3
votes
0
answers
71
views
Transverse intersection in the $G$-orbit of paths
I know how to prove the following lemma but I assume that it is well-known. Can someone provide a reference for it?
Let $d>1$ and let $M$ be a $d$-dimensional connected smooth manifold with a ...
- 5,382
4
votes
2
answers
219
views
Is $\mathbb{P}T^*M$ a sub-Riemannian manifold if $M$ is Riemannian?
(this question is about a particular aspect of a previous question, which was not duly stressed)
Let $(M,g)$ a Riemannian $n$-dimensional manifold, and let
$$
\widetilde{M}:=\mathbb{P}T^*M
$$
be the $...
- 2,527
4
votes
0
answers
318
views
Action of orthogonal group on the free Lie algebra
This question is somewhat related and inspired by this post of professor Montgomery.
The free Lie algebra $L(V)$ generated by an $r$-dimensional vector space $V$ is, in the language of https://en....
- 277
5
votes
1
answer
1k
views
On the complexification of a Riemannian manifold
Let $(M,g)$ be a Riemannian manifold and $TM$ be its tangent bundle. If we suppose $TM\otimes\mathbb{C}$ is the complexification of $TM$ then how can we define a natural metric on the complex bundle $...
- 601
1
vote
1
answer
145
views
Continuity of Busemann-Hausdorff area density
I am trying to find out why the Busemann-Hausdorff area density as defined by Burago and Ivanov is continuous. Here, $GC_m(V)\subset \Lambda^m(V)$ denotes the simple $m$-vectors in an $n$-dimensional ...
- 193