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This tag is used if a reference is needed in a paper or textbook on a specific result.

7 votes

Baum-Connes conjecture

I want to second David Ben-Zvi's recommendation of Nigel Higson's ICM lecture, though there is a bit of progress that has been published since it was written. Fortunately, you needn't venture further …
Paul Siegel's user avatar
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9 votes

Maxwell's equations and differential forms

I really strongly recommend chapter 2 of Naber's "Topology, Geometry, and Gauge Fields: Interactions". In this book and its companion volume "Topology, Geometry, and Gauge Fields: Foundations", Naber …
14 votes
3 answers
3k views

Reference Request: Relative De Rham Cohomology

I'm looking for a book, article, or lecture notes that does basic cohomology theory from a relative point of view (including the Thom isomorphism, the excision theorem, Lefschetz duality, the Gysin se …
Paul Siegel's user avatar
  • 29.2k
9 votes

Fascinating moments: equivalent mathematical discoveries

My personal favorite example of this phenomenon occurred in 1931. On one hand, Dirac published the paper Quantized Singularities in the Electromagnetic Field which hypothesized the existence of what …
16 votes
Accepted

Reference: Learning noncommutative geometry and C^* algebras

First of all, let me mention that functional analysis plays a similar role in noncommutative geometry that commutative algebra plays in algebraic geometry, and it pays off to at least have a reference …
Paul Siegel's user avatar
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2 votes
Accepted

The stabilized homotopy category of graded C* algebra

In what follows, all tensor products are graded. The comments about the existence of canonical (up to homotopy) $\ast$-homomorphisms $\mathbb{C} \to K(H)$ and $K(H) \otimes K(H) \to K(H)$ right befor …
Paul Siegel's user avatar
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2 votes
Accepted

Can C*-algebras be characterized among Banach *-algebras by the spectral radius?

[Updated to include Nik Weaver's correction / improvement from the comments.] I think this follows from the spectral radius formula: $$\left\| a \right\|^2 = \rho(a^*a) = \lim_{k \to \infty} \left\| …
Paul Siegel's user avatar
  • 29.2k
4 votes
Accepted

Interpretation of the two-dimensional de-Rham complex

After writing this, I noticed that Donu Arapura made essentially the same point in a comment. But perhaps my added detail will be of use. There are two missing ingredients in what you wrote. Firs …
Paul Siegel's user avatar
  • 29.2k
60 votes
Accepted

What is the significance of non-commutative geometry in mathematics?

$\DeclareMathOperator\coker{coker}$I think I'm in a pretty good position to answer this question because I am a graduate student working in noncommutative geometry who entered the subject a little bit …
Paul Siegel's user avatar
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8 votes

Advanced Differential Geometry Textbook

I would check out "Heat Kernels and Dirac Operators" by Berline, Getzler, and Verne. It covers quite a bit of territory: -Characteristic classes: Much stronger than most books; develops Chern-Weil t …
4 votes
Accepted

Gauge-theoretic formulation of Maxwell equations

I don't have my copy handy, but I think this is all worked out in chapter 2 of Naber's "Topology, Geometry, and Gauge Fields: Interactions". The book is essentially a textbook on differential geometr …
Paul Siegel's user avatar
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5 votes
Accepted

What is the role of $\sum (-1)^p[\wedge^pT^*M]$ in the K-theory $K(M)$

I think the main topological significance of the element you identify is its close relationship with the Thom isomorphism $K(M) \cong K(T^*M)$. I would imagine that there is also some connection with …
Paul Siegel's user avatar
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36 votes
Accepted

Analysis from a categorical perspective

I hesitate to let this out, but there's always this cute little note that I learned from another MO answer (I don't know which one): https://www.maths.ed.ac.uk/~tl/glasgowpssl/banach.pdf. Maybe this …
Paul Siegel's user avatar
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3 votes

Comments and reference-request on books for KK-theory

Here is a very rough outline of the proof of the index theorem using KK-theory: Define $KK_G(A, B)$, where $G$ is a Lie group and $A$ and $B$ are [adjectives] C*-algebras, and the Kasparov product be …
Paul Siegel's user avatar
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5 votes
Accepted

Regarding understanding differential geometry

I think the books "Topology, Geometry, and Gauge Fields: Foundations" and "Topology, Geometry, and Gauge Fields: Interactions" are exactly what you're looking for. They are not short, but you don't a …
Paul Siegel's user avatar
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