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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”.
1
vote
Accepted
Existence of an equivariant Morse function
This is discussed in
MR0250324 (40 #3563) Wasserman, Arthur G. Equivariant differential topology.
Topology 8 1969 127--150.
6
votes
Accepted
Is the action of diffeomorphisms transitive on the set of vector fields with prescribed zero...
Let me summarize the conclusions in the comments. This is rarely true:
There are local obstructions around fixed points: For example the order of vanishing (Andreas Cap), or the Hopf index of an isol …
17
votes
Accepted
Oriented vector bundle with odd-dimensional fibers
No.
Let us consider some vector bundles over $S^4$. Since $S^4$ is simply connected all vector bundles are oriented and rank $k$ vector bundles over $S^4$ are classified by $\pi_{3}(SO(k))$ by the cl …
3
votes
Separating two submanifolds
No, but if the codimension of the two submanifolds is high enough, then it is possible. Generically the intersection $A$ will be a submanifold of dimension $\dim(A)=\dim M+\dim N-\dim X$. Hence if t …
1
vote
Deforming Fredholm sections
Late to the party.
I would like to shamelessly advertise the work of Alberto Abbondandolo and me on non-linear Fredholm mappings [1,2]. This builds on work of Elworthy and Tromba [3].
Allow me to work …
9
votes
Accepted
The group structure on $[X,S^n]$ induced by the framed bordism
This is an answer to question (2). Let $n=0,1,3,7$ and $i=1,2$ and $d\leq 2n-2$. Let $e=(1,0,\ldots,0)\in S^n$
Let $f_i:X\rightarrow S^n$ be two maps representing framed submanifolds $(M_i,\nu_i)$. Le …
2
votes
Accepted
How does one identify flow lines on a vector bundle with those on the base in Morse theory?
The function $q$ strictly decreases along the solutions of the gradient flow outside of the zero section. Hence any orbit that starts outside the zero section will not converge to a critical point in …
5
votes
Accepted
restricting the "Whitney" map
No this is false, here is a counter example. Let $f:(\frac{1}{2},1)\times(0,4\pi)\rightarrow \mathbb{R}^2$ be given by $f(r,\theta)=(r \cos(\theta),r\sin(\theta))$. Of course the domain is diffeomorph …
4
votes
Accepted
A cobordism theory from Hirsch's "Differential Topology" (reference request)
As noted in the comments this is in Tom Diecks book (section 21.2), and in Wall's differential topology (Section 8.1).
5
votes
Accepted
Smooth circle actions on Riemannian manifolds and harmonicity of quotient map
I don't think so. I suspect that this action does not exists for generic metric $g$ on manifolds which admit circle actions.
Here is the thing that I have in mind.
Consider the two torus. This clearly …
6
votes
Accepted
When does a hypersurface have contact-type?
Not all hypersurfaces in $\mathbb{R}^{2n}$ are of contact type.
Weinstein, in the paper: "On the hypothesis of Rabinowitz' periodic orbit theorems", where he defined the concept of contact type, give …
49
votes
Accepted
Does there exist any non-contractible manifold with fixed point property?
Take the space $\mathbb{CP}^2$. Its cohomology ring is given by $\mathbb{Z}[a]/a^3$, where $a$ has degree $2$. A map $f:\mathbb{CP}^2\rightarrow \mathbb{CP}^2$ induces a map on the second cohomology g …
22
votes
Books in advanced differential topology
"Morse theory" by Milnor.
"Lectures on the h-cobordism theorem" by Milnor
"Characteristic classes" by Milnor and Stasheff.
"Topological methods in algebraic geometry" by Hirzebruch
"Fiber bundles" Hus …
5
votes
Patching up two trivial fibre bundles induces homology equivalence
I think you can do something like this. Let $Y=D^2$ be the open disc in the plane, $X=S^1$ the circle. Let $X_1$ a point on the circle (the red point below) and $X_2=X\setminus X_1$. Define the map as …
4
votes
Accepted
geometric conditions on maps between manifolds inducing monomorphisms on cohomology
Are you looking for things like the following?
Suppose $M$ and $N$ are of the same dimension connected, closed and $\mathbb{Z}/p\mathbb{Z}$ orientable. Suppose that the $(\mathbb{Z}/p\mathbb{Z})$ de …