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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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar

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