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Complex, contact, Riemannian, pseudo-Riemannian and Finsler geometry, relativity, gauge theory, global analysis.
12
votes
How much of differential geometry can be developed entirely without atlases?
Apart from Nestruev's book which is good but unfortunately very elementary,
I recommend you to take a look at Ramanan's Global Calculus.
Ramanan almost manages to avoid coordinates except for a few pl …
2
votes
Coordinate free proof of Gauss-Bonnet theorem
Yes. A beautiful conceptual coordinate-free proof is presented
by Berwick-Evans in https://arxiv.org/abs/1310.5383.
It obtains both sides of the Chern–Gauss–Bonnet theorem
as two limits of a partitio …
15
votes
How much of differential geometry can be developed entirely without atlases?
Your definition of a smooth manifold still uses atlases in a slightly
disguised way because it amounts to saying that a smooth manifold is a topological manifold with an open cover whose elements are …
6
votes
Groupoid objects in the category of derived manifolds
Would this be of any interest to solve some geometric questions. Is there a notion of "derived stack" in the differential geometry setting.
The notion of a derived stack in the setting of differenti …
4
votes
Accepted
Why is the transgression of differential forms a form?
After integration we have a number so isn't it a function?
Differential $k$-forms can be integrated along a submersion with $d$-dimensional fibers, which yields a differential $(k-d)$-form.
Fiberwis …
4
votes
Morita equivalent Lie groupoids
I will answer the new version of the question:
Does $\ker(\varphi_{*,a})=\ker (\phi_{*,a})$ for all $a\in P$,
where $\phi_{*,a}:T_aP\to T_{\phi(a)}X_0$ and $\varphi_{*,a}:T_aP\to T_{\varphi(a)}Y_0$ a …
8
votes
What properties should $C(M,\mathbb{R})$ have when $M$ is a $n$-dimensional manifold?
For compact orientable manifolds, this is accomplished by the notion of a spectral triple.
See the question Commutative spectral triples for additional information, including a precise statement of th …
1
vote
Non-unital algebras in geometric algebra, smooth envelopes
For example: is the notion of a smooth envelope of a geometric R-algebra F well-defined if F lacks a unit?
Yes. Recall the construction: $F$ is geometric if the Gelfand homomorphism
$$\def\Map{\mat …
9
votes
Accepted
Is there an easy way to describe the sheaf of smooth functions on a product manifold?
Smooth manifolds are affine, thus the sheaf of smooth functions is determined by its global sections.
Now C^∞(M×N)=C^∞(M)⊗C^∞(N).
The tensor product here is the projective tensor product
of complete l …
2
votes
Accepted
Regarding first order differential operator and derivative endomorphism
Substituting $f=f_1f_2$ in the definition of a derivative endomorphism immediately implies that $D_M$ is a derivation, using the fact that $g_1ψ=g_2ψ$ for all vector fields $ψ$ implies $g_1=g_2$, wher …
7
votes
Integration of differential forms using measure theory?
Yes, Lp-spaces can be defined for arbitrary hermitian vector bundles.
For the sake of convenience I denote Lp=L1/p (see this answer for a motivation), in particular L0=L∞ and L1/2=L2.
As explained in …
6
votes
Analogue of vector for differential operators
Yes. If $E→M$ and $F→M$ are vector bundles over a smooth manifold $M$, then differential operators $E→F$ of order less than $k≥0$ can be identified with sections of a finite-dimensional vector bundle …
3
votes
Accepted
One-to-one correspondence between super morphisms $\varphi:S\to TX$ and pairs $(f:C^\infty(X...
The morphism $$\def\T{{\rm T}} φ:S→\T X$$ can be identified with the homomorphism of algebras $$\def\Ci{{\rm C}^∞} \Ci(\T X)→\Ci(S).$$
The algebra $\Ci(\T X)$ can be identified with the $\Ci$-symmetri …
21
votes
Accepted
Real manifolds and affine schemes
(1) This is a highly productive way of looking at smooth manifolds.
It is responsible for synthetic differential geometry and derived smooth manifolds.
Both of these subjects heavily rely on this iden …
3
votes
A k-form is thought of as measuring the flux through an infinitesimal k-parallelepiped
See Theorem 1 in Anders Kock's paper
“Differential forms as infinitesimal cochains”,
which is devoted precisely to this question.
Specifically, the map b in the formula (1)
establishes an explicit bij …