Skip to main content
Search type Search syntax
Tags [tag]
Exact "words here"
Author user:1234
user:me (yours)
Score score:3 (3+)
score:0 (none)
Answers answers:3 (3+)
answers:0 (none)
isaccepted:yes
hasaccepted:no
inquestion:1234
Views views:250
Code code:"if (foo != bar)"
Sections title:apples
body:"apples oranges"
URL url:"*.example.com"
Saves in:saves
Status closed:yes
duplicate:no
migrated:no
wiki:no
Types is:question
is:answer
Exclude -[tag]
-apples
For more details on advanced search visit our help page
Results tagged with
Search options not deleted user 12482

Complex, contact, Riemannian, pseudo-Riemannian and Finsler geometry, relativity, gauge theory, global analysis.

3 votes

A Lie group whose Lie algebra is equal to (the Lie algebra? of )all functions with fibrewise...

The following will only deal with the Lie algebra, the question about the Lie group is far beyond my capabilities. The symplectic structure is (I guess) the one coming from the musical isomorphism of …
Stefan Waldmann's user avatar
16 votes
Accepted

Hodge decomposition of smooth n-forms: is it an isomorphism of topological vector spaces?

Maybe an even more elementary argument than the one of Tobias: The continuity of all involved operators is easy: simply all differential operators with smooth coefficients between sections of vector b …
Stefan Waldmann's user avatar
4 votes
Accepted

Hermitian vector bundles and Hilbert $C^*$-modules

In addition to Nik Weaver's references, let me just sketch the proof which is in fact not very difficult: A construction of Kaplansky (Rings of operators, Thm 26) shows that if $\mathcal{A}$ is a $*$ …
Stefan Waldmann's user avatar
10 votes

How special are homogeneous spaces?

I suppose you want the action to be transitive as your title suggests. In this case, a classical theorem of Mostow (in 1950 for surfaces, in 2005 in general) says that for a compact homogeneous space …
Stefan Waldmann's user avatar
8 votes

When (why) did we allow manifolds to be non-Hausdorff and/or non-second countable?

Non-Hausdorffness shows up in several contexts when dealing with Lie groupoids: the integration (Lie's 3rd Theorem) for Lie algebroids to Lie groupoids will typically produce a non-Hausdorff one, if i …
Stefan Waldmann's user avatar
4 votes

Interpretation of the Schouten bracket as an integrability condition

One well-known example is the case of bivector fiels $\pi$. Then $[\pi, \pi] = 0$ is equivalent to say that $\{f, g\} = \pi(df, dg)$ is a Poisson bracket, i.e. satisfies the Jacobi identity. In this …
Stefan Waldmann's user avatar
5 votes

Formal adjoint of the covariant derivative

Being a bit late for the party, here is nevertheless a small answer. In fact, there is a rather explicit way to compute adjoints of every differential operator (any order) between (smooth, compactly s …
Stefan Waldmann's user avatar
13 votes
Accepted

On the topology induced by a Lorentzian metric

In general, this topology is coarser than the original topology of the manifold, and, without further assumptions, strictly coarser. It coincides with the original one iff the Lorentz manifold is stro …
Stefan Waldmann's user avatar
8 votes
2 answers
433 views

On the causal structure of spacetimes: piecewise $C^1$, $C^k$ or $C^\infty$?

This is a more technical question but it seems that there is some confusion in the literature on the choice of curves used to define the causal relations in time-oriented Lorentz manifolds: the infini …
Stefan Waldmann's user avatar
9 votes

A vector field on the tangent bundle which is not equivalent to any second order ODE

I guess you want the topological equivalence to preserve the bundle structure of $TM \longrightarrow M$ otherwise it becomes a bit arbitrary, right? In this case a non-zero vertical vector field will …
Stefan Waldmann's user avatar
14 votes
Accepted

What do the differential k-forms on a product manifold look like?

Denote by $p_M: M \times N \longrightarrow M$ and $p_N: M \times N \longrightarrow N$ the canonical projections. Then you get an induced bilinear map from $\Omega^i(M) \times \Omega^j(N) \longrightarr …
Stefan Waldmann's user avatar
2 votes
Accepted

Poisson structure on the dual Lie algebroid

Depending on you sign convention, this goes as follows. First you denote the bundle projection by $pr\colon E^* \longrightarrow X$. For a section $s \in \Gamma^\infty(E)$ you have a linear function $J …
Stefan Waldmann's user avatar
9 votes
1 answer
2k views

Automorphism group of a fiber bundle surjects onto diffeomorphism group?

This should surely be well-known by I have not been able to find a good reference to the following question: Given a smooth fiber bundle $\pi\colon P \longrightarrow M$ over a smooth manifold $M$ with …
Stefan Waldmann's user avatar
3 votes
Accepted

Horizontal lift of differential operator

This is a sort of standard construction you can find in several places. I don't know where this was done first though... OK: first you can extend your horizontal lift from vector fields to all (symm …
Stefan Waldmann's user avatar
6 votes
0 answers
201 views

The geometric shape of domains of flows

Consider a smooth (non-compact) manifold $M$ with a vector field $X$. Then we know that there is a open neighbourhood $U \subseteq M \times \mathbb{R}$ of $M \times \{0\}$ such that on $U$ the flow $\ …
Stefan Waldmann's user avatar

15 30 50 per page