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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
Accepted
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. …
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 …
14
votes
Accepted
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 …
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 …
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. …
6
votes
Accepted
Are cohomology functors sheaves?
"in what way is cohomology a sheaf" leads one to notions like ∞-topoi etc. …
6
votes
Accepted
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 …
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. …
2
votes
Accepted
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 …
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? …
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. …