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The study of differentiable manifolds and differentiable maps. One fundamental problem is that of classifying manifolds up to diffeomorphism. Differential topology is what Poincaré understood as topology or “analysis situs”.

21 votes
3 answers
2k views

Manifolds with polynomial transition maps

Title edited I thank მამუკა ჯიბლაძე and Corbennick for their suggestion on the title of this question. I changed the title based on the suggestion of Corbennick. What is an example of a m …
Ali Taghavi's user avatar
11 votes
Accepted

Are there vector fields which are gradients with respect to one metric but not another?

Consider the vector field $$X=(y-10x)\partial_x-x\partial_y$$ it is not a gradient vector field with respect to the standard Riemannian metric of $\mathbb{R}^2$ but it is a gradient …
Ali Taghavi's user avatar
10 votes
1 answer
385 views

A symmetric embedding of manifolds

Assume that $M$ is a manifold. Is there an embedding of $M$ in some $\mathbb{R}^{n}$ such that the image of $M$ in $\mathbb{R}^{n}$ is invariant under each reflection $(x_{1},x_{2},\ldots x_{i},\l …
Ali Taghavi's user avatar
10 votes
2 answers
347 views

A quantity associated with a smooth groupoid

Assume that $(G,G^0,r,s)$ is a smooth groupoid such that $G$ is a compact connected manifold. The graph of "source" and "range" maps $s, r: G \to G^0$ are compact submanifolds $S$ and $R$ of $G\times …
Ali Taghavi's user avatar
7 votes
1 answer
613 views

Compactification of open manifolds in the form of a manifold( with zero Euler characteristic)

Edit: According to the interesting comments of Michael Albanese and Nick L we revise the question as follows: By manifold compactification of a manifold $M$ we mean a compact manifold $\tilde{M}$ whi …
Ali Taghavi's user avatar
6 votes
2 answers
435 views

The convex hull of a manifold whose cobordism class is trivial

Let $M$ be a compact orientable $n$ dimensional manifold. Assume that $M$ has trivial cobordism class. Is there an embedding of $M$ in some Euclidean space $\mathbb{R}^m$ such that the convex hul …
Ali Taghavi's user avatar
6 votes
0 answers
291 views

Can we "Curve" a manifold, as much as possible?

Assume that $M$ is a $k$ dimensional manifold which is embedded in $\mathbb{R}^n$. We define the map $\phi_{M,n}: M \to G(k,n)$ with $\phi_{M,n} (x)= T_x M$, the tangent space to $M$ at point $x\in M$ …
Ali Taghavi's user avatar
5 votes
1 answer
372 views

A possible characterization of sphere or projective space

Is there a compact Riemanian manifold $M$ not diffeomorphic to sphere or real or complex or quaternion projective space which admit a diffeomorphism $f$ with the property that $$\forall x \in M, \qu …
Ali Taghavi's user avatar
5 votes
2 answers
384 views

Nash isometric embedding theorem with keeping the symplectic structures of our ambient spaces

I apologize in advance if this question has an obvious answer. Let $(M,g)$ be a Riemannian manifold. Then the tangent bundle $TM$ carries a natural symplectic structure $\omega_g$. In fact $\omega_g …
Ali Taghavi's user avatar
5 votes
2 answers
448 views

Is $TS^n$ diffeomorphic to an open subset of $\mathbb{R}^{2n}$

For what values of $n \neq 1,3,7$ is the tangent bundle $TS^n$ of the $n$-sphere diffeomorphic to an open subset of $\mathbb{R}^{2n}$?
Ali Taghavi's user avatar
5 votes
1 answer
385 views

No analytic surjection $f:M \to N$ when $\dim(M) >\dim(N)$

Inspired by comment discussions in this MO post smooth version of splitting principle we ask: Are there two compact real analytic manifolds $M,N$ of dimension $m>n$ such that there is not any analyti …
Ali Taghavi's user avatar
4 votes
2 answers
165 views

functions which covers(good covers) manifolds

Let $M$ be a (not necessarily compact)) smooth manifold. 1.Is there a smooth map $f:M\to \mathbb{R}$ and an open covering $\mathbb{R}=\cup U_{\alpha}$ such that each $f^{-1}(U_{\alpha})$ i …
Ali Taghavi's user avatar
4 votes
1 answer
451 views

The maximum number of vertical independent vector fields on the tangent bundle

Let $M$ be a differentiable manifold. Is there a name for the maximum number of globally defined independent vector fields on $TM$ which are tangent to the fibers of $TM\to M$? Is there a name for th …
Ali Taghavi's user avatar
4 votes
0 answers
149 views

Higher tangent bundles of manifolds with non integer dimension

One way to define the tangent space of a manifold at a point $p\in M$ is the following: We define an equivalent relation on the space of curves passing $p$ as follows: Two curves $\alpha, \beta$ are …
Ali Taghavi's user avatar
3 votes
1 answer
344 views

On functional equation $f\circ \exp=\exp \circ Df$ on a Riemannian manifold or a Lie Group

Let $M$ be a Riemannian manifold or a Lie group whose corresponding exp map (in corresponding context) is denoted by "exp" which is a map $\exp:TM\to M$ We search for the set $\mathcal{H …
Ali Taghavi's user avatar

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