In algebraic geometry, the cohomology of a stack is a generalization of
étale cohomology
In mathematics, the étale cohomology groups of an algebraic variety or scheme are algebraic analogues of the usual cohomology groups with finite coefficients of a topological space, introduced by Grothendieck in order to prove the Weil conjectu ...
. In a sense, it is a theory that is coarser than the
Chow group of a stack In algebraic geometry, the Chow group of a stack is a generalization of the Chow group of a variety or scheme to stacks. For a quotient stack X = /G/math>, the Chow group of ''X'' is the same as the ''G''-equivariant Chow group of ''Y''.
A key d ...
.
The cohomology of a
quotient stack In algebraic geometry, a quotient stack is a stack (mathematics), stack that parametrizes equivariant objects. Geometrically, it generalizes a quotient of a Scheme (mathematics), scheme or a algebraic variety, variety by a Group (mathematics), group ...
(e.g.,
classifying stack In algebraic geometry, a quotient stack is a stack that parametrizes equivariant objects. Geometrically, it generalizes a quotient of a scheme or a variety by a group: a quotient variety, say, would be a coarse approximation of a quotient stack.
...
) can be thought of as an algebraic counterpart of
equivariant cohomology In mathematics, equivariant cohomology (or ''Borel cohomology'') is a cohomology theory from algebraic topology which applies to topological spaces with a ''group action''. It can be viewed as a common generalization of group cohomology and an ord ...
. For example,
Borel's theorem states that the cohomology ring of a
classifying stack In algebraic geometry, a quotient stack is a stack that parametrizes equivariant objects. Geometrically, it generalizes a quotient of a scheme or a variety by a group: a quotient variety, say, would be a coarse approximation of a quotient stack.
...
is a polynomial ring.
See also
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l-adic sheaf
*
smooth topology
References
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{{algebraic-geometry-stub
Algebraic geometry
Cohomology theories