In
mathematics, Artin–Verdier duality is a
duality theorem for constructible abelian
sheaves over the
spectrum of a ring of
algebraic numbers, introduced by , that generalizes
Tate duality In mathematics, Tate duality or Poitou–Tate duality is a duality theorem for Galois cohomology groups of modules over the Galois group of an algebraic number field or local field, introduced by and .
Local Tate duality
For a ''p''-adic local f ...
.
It shows that, as far as
etale (or
flat
Flat or flats may refer to:
Architecture
* Flat (housing), an apartment in the United Kingdom, Ireland, Australia and other Commonwealth countries
Arts and entertainment
* Flat (music), a symbol () which denotes a lower pitch
* Flat (soldier), ...
)
cohomology
In mathematics, specifically in homology theory and algebraic topology, cohomology is a general term for a sequence of abelian groups, usually one associated with a topological space, often defined from a cochain complex. Cohomology can be viewe ...
is concerned, the
ring of integers in a
number field
In mathematics, an algebraic number field (or simply number field) is an extension field K of the field of rational numbers such that the field extension K / \mathbb has finite degree (and hence is an algebraic field extension).
Thus K is a f ...
behaves like a
3-dimensional
Three-dimensional space (also: 3D space, 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called ''parameters'') are required to determine the position of an element (i.e., point). This is the informal ...
mathematical object
A mathematical object is an abstract concept arising in mathematics.
In the usual language of mathematics, an ''object'' is anything that has been (or could be) formally defined, and with which one may do deductive reasoning and mathematical p ...
.
Statement
Let ''X'' be the
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
of the
ring of integers in a
totally imaginary number field
In mathematics, an algebraic number field (or simply number field) is an extension field K of the field of rational numbers such that the field extension K / \mathbb has finite degree (and hence is an algebraic field extension).
Thus K is a f ...
''K'', and ''F'' a
constructible étale abelian sheaf on ''X''. Then the
Yoneda pairing
:
is a
non-degenerate pairing of finite abelian groups, for every integer ''r''.
Here, ''H
r''(''X,F'') is the ''r''-th
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 conjectur ...
group of the
scheme ''X'' with values in ''F,'' and Ext''
r''(''F,G'') is the group of ''r''-
extensions
Extension, extend or extended may refer to:
Mathematics
Logic or set theory
* Axiom of extensionality
* Extensible cardinal
* Extension (model theory)
* Extension (predicate logic), the set of tuples of values that satisfy the predicate
* E ...
of the étale sheaf ''G'' by the étale sheaf ''F'' in the
category
Category, plural categories, may refer to:
Philosophy and general uses
*Categorization, categories in cognitive science, information science and generally
* Category of being
* ''Categories'' (Aristotle)
* Category (Kant)
* Categories (Peirce) ...
of étale abelian sheaves on ''X.'' Moreover, ''G
m'' denotes the étale sheaf of
units
Unit may refer to:
Arts and entertainment
* UNIT, a fictional military organization in the science fiction television series ''Doctor Who''
* Unit of action, a discrete piece of action (or beat) in a theatrical presentation
Music
* Unit (album), ...
in the
structure sheaf of ''X.''
proved Artin–Verdier duality for constructible, but not necessarily torsion sheaves. For such a sheaf ''F'', the above pairing induces isomorphisms
:
where
:
Finite flat group schemes
Let ''U'' be an open subscheme of the spectrum of the ring of integers in a number field ''K'', and ''F'' a finite flat commutative
group scheme
In mathematics, a group scheme is a type of object from algebraic geometry equipped with a composition law. Group schemes arise naturally as symmetries of schemes, and they generalize algebraic groups, in the sense that all algebraic groups have ...
over ''U''. Then the
cup product In mathematics, specifically in algebraic topology, the cup product is a method of adjoining two cocycles of degree ''p'' and ''q'' to form a composite cocycle of degree ''p'' + ''q''. This defines an associative (and distributive) graded commutati ...
defines a non-degenerate pairing
:
of finite abelian groups, for all integers ''r''.
Here ''F
D'' denotes the
Cartier dual of ''F'', which is another finite flat commutative group scheme over ''U''. Moreover,
is the ''r''-th
flat cohomology In mathematics, the flat topology is a Grothendieck topology used in algebraic geometry. It is used to define the theory of flat cohomology; it also plays a fundamental role in the theory of descent (category theory), descent (faithfully flat descen ...
group of the scheme ''U'' with values in the flat abelian sheaf ''F'', and
is the ''r''-th ''flat cohomology with compact supports'' of ''U'' with values in the flat abelian sheaf ''F.''
The ''flat cohomology with compact supports'' is defined to give rise to a long exact sequence
:
The sum is taken over all
places
Place may refer to:
Geography
* Place (United States Census Bureau), defined as any concentration of population
** Census-designated place, a populated area lacking its own municipal government
* "Place", a type of street or road name
** Ofte ...
of ''K'', which are not in ''U'', including the archimedean ones. The local contribution ''H
r''(''K
v'', ''F'') is the
Galois cohomology In mathematics, Galois cohomology is the study of the group cohomology of Galois modules, that is, the application of homological algebra to modules for Galois groups. A Galois group ''G'' associated to a field extension ''L''/''K'' acts in a natur ...
of the
Henselization ''K
v'' of ''K'' at the place ''v'', modified a la
Tate
Tate is an institution that houses, in a network of four art galleries, the United Kingdom's national collection of British art, and international modern and contemporary art. It is not a government institution, but its main sponsor is the U ...
:
:
Here
is a separable closure of
References
*
*
*
*
{{DEFAULTSORT:Artin-Verdier duality
Theorems in number theory
Duality theories