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A branch of algebraic topology concerning the study of cocycles and coboundaries. It is in some sense a dual theory to homology theory. This tag can be further specialized by using it in conjunction with the tags group-cohomology, etale-cohomology, sheaf-cohomology, galois-cohomology, lie-algebra-cohomology, motivic-cohomology, equivariant-cohomology, ...

18 votes
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A non-Abelian de Rham complex?

If G is an abelian Lie group, we get the Deligne complex, used to define bundle n-gerbes with connection, alias Deligne cohomology. …
Dmitri Pavlov's user avatar
15 votes
0 answers
706 views

Is there an expository account of homology of simplicial sets that does not assume prior fam...

There are numerous expositions of simplicial homology in the literature. Munkres in “Elements of Algebraic Topology” develops the homology theory of simplicial complexes. Hatcher in “Algebraic Topol …
Dmitri Pavlov's user avatar
14 votes
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De Rham via topoi

One can define an analogue of the crystalline topos for smooth manifolds. This is known as the de Rham stack of $M$. One of the easiest constructions of the de Rham stack embeds smooth manifolds fully …
Dmitri Pavlov's user avatar
10 votes
1 answer
3k views

De Rham homology

Suppose M is an arbitrary smooth manifold and D is its bundle of 1-densities. On the category of finite-dimensional vector bundles over M and linear differential operators between them there is a cont …
Dmitri Pavlov's user avatar
6 votes

Group cohomology version of Deligne-Beilinson cohomology

The nth Deligne cohomology is defined as cohomology with coefficients in a truncated chain complex of sheaves of U(1)-valued differential forms: U(1)→Ω^1→Ω^2→⋯→Ω^n for some n≥0. … This defines a nonabelian analog of the Deligne cohomology for any choice of the underlying site: smooth, holomorphic, algebraic. …
Dmitri Pavlov's user avatar
6 votes
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Are cohomology functors sheaves?

"in what way is cohomology a sheaf" leads one to notions like ∞-topoi etc. …
Dmitri Pavlov's user avatar
6 votes
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Why should we study the total complex?

Chain complexes arise from simplicial abelian groups via the Dold–Kan correspondence: the normalized chain complex functor establishes an equivalence of categories from simplicial abelian groups to (n …
Dmitri Pavlov's user avatar
2 votes

Are Chern classes well defined up to contractible choice?

In “Chern–Weil forms and abstract homotopy theory”, Freed and Hopkins compute the de Rham cohomology of $\def\B{{\sf B}}\B_∇ G$, the moduli stack (in groupoids) of principal $G$-bundles with connections … The de Rham cohomology of $\B_∇ G$ turns out to be isomorphic to the graded algebra of $G$-invariant polynomials (placed in even degrees) on the Lie algebra of $G$, with the zero differential. …
Dmitri Pavlov's user avatar
2 votes
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Coefficient (or target) category for factorization homology

One rich source of examples is that every combinatorial symmetric monoidal model category gives rise to such a category V. In particular, this covers all the examples in the main post, including cdga …
Dmitri Pavlov's user avatar
2 votes

How does Cech cohomology get around computing a delooping?

In derived functor cohomology one takes cochain resolutions of A, which again by co-Dold-Kan is the same thing as cosimplicial resolutions. Can one also do this the nonabelian setting? …
Dmitri Pavlov's user avatar
1 vote

How to compute cup product of derived limits / presheaf cohomology

Cup products in sheaf (and presheaf) cohomology are often easy to compute by resolving the source (in the projective model structure, say), not the target. …
Dmitri Pavlov's user avatar