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{{Group theory sidebar |Algebraic}} | |||
In [[mathematics]], particularly in [[algebraic geometry]], [[complex analysis]] and [[number theory]], an '''abelian variety''' is a [[Algebraic variety#Projective variety|projective algebraic variety]] that is also an [[algebraic group]], i.e., has a [[group law]] that can be defined by [[regular function]]s. Abelian varieties are at the same time among the most studied objects in algebraic geometry and indispensable tools for much research on other topics in algebraic geometry and number theory. | |||
An abelian variety can be defined by equations having coefficients in any [[Field (mathematics)|field]]; the variety is then said to be defined ''over'' that field. Historically the first abelian varieties to be studied were those defined over the field of [[complex numbers]]. Such abelian varieties turn out to be exactly those [[Complex torus|complex tori]] that can be embedded into a complex [[projective space]]. Abelian varieties defined over [[algebraic number fields]] are a special case, which is important also from the viewpoint of number theory. [[Localization of a ring|Localization]] techniques lead naturally from abelian varieties defined over number fields to ones defined over [[finite field]]s and various [[local field]]s. | |||
Abelian varieties appear naturally as [[Jacobian variety|Jacobian varieties]] (the connected components of zero in [[Picard variety|Picard varieties]]) and [[Albanese variety|Albanese varieties]] of other algebraic varieties. The group law of an abelian variety is necessarily [[commutative]] and the variety is [[non-singular]]. An [[elliptic curve]] is an abelian variety of dimension 1. Abelian varieties have [[Kodaira dimension]] 0. | |||
== History and motivation == | |||
{{details|History of manifolds and varieties}} | |||
In the early nineteenth century, the theory of [[elliptic function]]s succeeded in giving a basis for the theory of [[elliptic integral]]s, and this left open an obvious avenue of research. The standard forms for elliptic integrals involved the [[square root]]s of [[cubic polynomial|cubic]] and [[quartic polynomial]]s. When those were replaced by polynomials of higher degree, say [[quintic polynomial|quintics]], what would happen? | |||
In the work of [[Niels Abel]] and [[Carl Gustav Jakob Jacobi|Carl Jacobi]], the answer was formulated: this would involve functions of [[two complex variables]], having four independent ''periods'' (i.e. period vectors). This gave the first glimpse of an abelian variety of dimension 2 (an '''abelian surface'''): what would now be called the ''Jacobian of a [[hyperelliptic curve]] of genus 2''. | |||
After Abel and Jacobi, some of the most important contributors to the theory of abelian functions were [[Bernhard Riemann|Riemann]], [[Karl Weierstrass|Weierstrass]], [[Ferdinand Georg Frobenius|Frobenius]], [[Henri Poincaré|Poincaré]] and [[Charles Émile Picard|Picard]]. The subject was very popular at the time, already having a large literature. | |||
By the end of the 19th century, mathematicians had begun to use geometric methods in the study of abelian functions. Eventually, in the 1920s, [[Solomon Lefschetz|Lefschetz]] laid the basis for the study of abelian functions in terms of complex tori. He also appears to be the first to use the name "abelian variety". It was [[André Weil]] in the 1940s who gave the subject its modern foundations in the language of algebraic geometry. | |||
Today, abelian varieties form an important tool in number theory, in [[dynamical system]]s (more specifically in the study of [[Hamiltonian system]]s), and in algebraic geometry (especially [[Picard variety|Picard varieties]] and [[Albanese variety|Albanese varieties]]). | |||
== Analytic theory == | |||
=== Definition === | |||
A complex torus of dimension ''g'' is a [[torus]] of real dimension 2''g'' that carries the structure of a [[complex manifold]]. It can always be obtained as the [[quotient space|quotient]] of a ''g''-dimensional complex [[vector space]] by a [[Lattice (group)|lattice]] of rank 2''g''. | |||
A complex abelian variety of dimension ''g'' is a complex torus of dimension ''g'' that is also a projective [[algebraic variety]] over the field of complex numbers. Since they are complex tori, abelian varieties carry the structure of a [[group (mathematics)|group]]. A [[morphism]] of abelian varieties is a morphism of the underlying algebraic varieties that preserves the [[identity element]] for the group structure. An '''isogeny''' is a finite-to-one morphism. | |||
When a complex torus carries the structure of an algebraic variety, this structure is necessarily unique. In the case ''g'' = 1, the notion of abelian variety is the same as that of [[elliptic curve]], and every complex torus gives rise to such a curve; for ''g'' > 1 it has been known since [[Bernhard Riemann|Riemann]] that the algebraic variety condition imposes extra constraints on a complex torus. | |||
=== Riemann conditions === | |||
The following criterion by Riemann decides whether or not a given complex torus is an abelian variety, i.e. whether or not it can be embedded into a projective space. Let ''X'' be a ''g''-dimensional torus given as ''X'' = ''V''/''L'' where ''V'' is a complex vector space of dimension ''g'' and ''L'' is a lattice in ''V''. Then ''X'' is an abelian variety if and only if there exists a [[positive definite bilinear form|positive definite]] [[hermitian form]] on ''V'' whose [[imaginary part]] takes [[integer|integral]] values on ''L''×''L''. Such a form on ''X'' is usually called a (non-degenerate) [[Riemann form]]. Choosing a basis for ''V'' and ''L'', one can make this condition more explicit. There are several equivalent formulations of this; all of them are known as the Riemann conditions. | |||
=== The Jacobian of an algebraic curve === | |||
Every algebraic curve ''C'' of [[genus (mathematics)|genus]] ''g'' ≥ 1 is associated with an abelian variety ''J'' of dimension ''g'', by means of an analytic map of ''C'' into ''J''. As a torus, ''J'' carries a commutative [[group (mathematics)|group]] structure, and the image of ''C'' generates ''J'' as a group. More accurately, ''J'' is covered by ''C''<sup>''g''</sup>: any point in ''J'' comes from a ''g''-tuple of points in ''C''. The study of differential forms on ''C'', which give rise to the ''[[abelian integral]]s'' with which the theory started, can be derived from the simpler, translation-invariant theory of differentials on ''J''. The abelian variety ''J'' is called the '''Jacobian variety''' of ''C'', for any non-singular curve ''C'' over the complex numbers. From the point of view of [[birational geometry]], its [[function field of an algebraic variety|function field]] is the fixed field of the [[symmetric group]] on ''g'' letters acting on the function field of ''C''<sup>''g''</sup>. | |||
=== Abelian functions === | |||
An '''abelian function''' is a [[meromorphic function]] on an abelian variety, which may be regarded therefore as a periodic function of ''n'' complex variables, having 2''n'' independent periods; equivalently, it is a function in the function field of an abelian variety. | |||
For example, in the nineteenth century there was much interest in [[hyperelliptic integral]]s that may be expressed in terms of elliptic integrals. This comes down to asking that ''J'' is a product of elliptic curves, [[up to]] an isogeny. | |||
{{See also|abelian integral}} | |||
== Algebraic definition == | |||
Two equivalent definitions of abelian variety over a general field ''k'' are commonly in use: | |||
* a [[connected space|connected]] and [[Complete variety|complete]] [[algebraic group]] over ''k'' | |||
* a [[connected space|connected]] and [[Algebraic geometry|projective]] [[algebraic group]] over ''k''. | |||
When the base is the field of complex numbers, these notions coincide with the previous definition. Over all bases, [[elliptic curve]]s are abelian varieties of dimension 1. | |||
In the early 1940s, Weil used the first definition (over an arbitrary base field) but could not at first prove that it implied the second. Only in 1948 did he prove that complete algebraic groups can be embedded into projective space. Meanwhile, in order to make the proof of the [[Generalised Riemann hypothesis|Riemann hypothesis]] for [[algebraic curve|curves]] over [[finite field]]s that he had announced in 1940 work, he had to introduce the notion of an [[abstract variety]] and to rewrite the foundations of algebraic geometry to work with varieties without projective embeddings (see also the history section in the [[Algebraic Geometry]] article). | |||
== Structure of the group of points == | |||
By the definitions, an abelian variety is a group variety. Its group of points can be proven to be [[abelian group|commutative]]. | |||
For '''C''', and hence by the [[Lefschetz principle]] for every [[algebraically closed field]] of [[characteristic (algebra)|characteristic]] zero, the [[torsion group]] of an abelian variety of dimension ''g'' is [[isomorphic]] to ('''Q'''/'''Z''')<sup>2''g''</sup>. Hence, its ''n''-torsion part is isomorphic to ('''Z'''/''n'''''Z''')<sup>2''g''</sup>, i.e. the product of 2''g'' copies of the [[cyclic group]] of order ''n''. | |||
When the base field is an algebraically closed field of characteristic ''p'', the ''n''-torsion is still isomorphic to ('''Z'''/''n'''''Z''')<sup>2''g''</sup> when ''n'' and ''p'' are [[coprime]]. When ''n'' and ''p'' are not coprime, the same result can be recovered provided one interprets it as saying that the ''n''-torsion defines a finite flat group scheme of rank ''2g''. If instead of looking at the full scheme structure on the ''n''-torsion, one considers only the geometric points, one obtains a new invariant for varieties in characteristic ''p'' (the so-called ''p''-rank when ''n = p''). | |||
The group of [[rational point|''k''-rational points]] for a [[global field]] ''k'' is [[finitely generated group|finitely generated]] by the [[Mordell-Weil theorem]]. Hence, by the structure theorem for [[finitely generated abelian group]]s, it is isomorphic to a product of a [[free abelian group]] '''Z'''<sup>''r''</sup> and a finite commutative group for some non-negative integer ''r'' called the '''rank''' of the abelian variety. Similar results hold for some other classes of fields ''k''. | |||
==Products== | |||
The product of an abelian variety ''A'' of dimension ''m'', and an abelian variety ''B'' of dimension ''n'', over the same field, is an abelian variety of dimension ''m'' + ''n''. An abelian variety is '''simple''' if it is not [[isogeny|isogenous]] to a product of abelian varieties of lower dimension. Any abelian variety is isogenous to a product of simple abelian varieties. | |||
== Polarisation and dual abelian variety == | |||
=== Dual abelian variety === | |||
{{main|Dual abelian variety}} | |||
To an abelian variety ''A'' over a field ''k'', one associates a '''dual abelian variety''' ''A''<sup>v</sup> (over the same field), which is the solution to the following [[moduli problem]]. A family of degree 0 line bundles parametrised by a ''k''-variety ''T'' is defined to be a [[line bundle]] ''L'' on | |||
''A''×''T'' such that | |||
# for all ''t'' in ''T'', the restriction of ''L'' to ''A''×{''t''} is a degree 0 line bundle, | |||
# the restriction of ''L'' to {0}×''T'' is a trivial line bundle (here 0 is the identity of ''A''). | |||
Then there is a variety ''A''<sup>v</sup> and a family of degree 0 line bundles ''P'', the Poincaré bundle, parametrised by ''A''<sup>v</sup> such that a family ''L'' on ''T'' is associated a unique morphism ''f'': ''T'' → ''A''<sup>v</sup> so that ''L'' is isomorphic to the pullback of ''P'' along the morphism 1<sub>A</sub>×''f'': ''A''×''T'' → ''A''×''A''<sup>v</sup>. Applying this to the case when ''T'' is a point, we see that the points of ''A''<sup>v</sup> correspond to line bundles of degree 0 on ''A'', so there is a natural group operation on ''A''<sup>v</sup> given by tensor product of line bundles, which makes it into an abelian variety. | |||
This association is a duality in the sense that there is a [[natural isomorphism]] between the double dual ''A''<sup>vv</sup> and ''A'' (defined via the Poincaré bundle) and that it is [[contravariant functor]]ial, i.e. it associates to all morphisms ''f'': ''A'' → ''B'' dual morphisms ''f''<sup>v</sup>: ''B''<sup>v</sup> → ''A''<sup>v</sup> in a compatible way. The ''n''-torsion of an abelian variety and the ''n''-torsion of its dual are [[Pontryagin duality|dual]] to each other when ''n'' is coprime to the characteristic of the base. In general - for all ''n'' - the ''n''-torsion [[group scheme]]s of dual abelian varieties are [[Cartier dual]]s of each other. This generalises the [[Weil pairing]] for elliptic curves. | |||
=== Polarisations === | |||
A '''polarisation''' of an abelian variety is an ''[[isogeny]]'' from an abelian variety to its dual that is symmetric with respect to ''double-duality'' for abelian varieties and for which the pullback of the Poincaré bundle along the associated graph morphism is ample (so it is analogous to a positive-definite quadratic form). Polarised abelian varieties have finite [[automorphism group]]s. A '''principal polarisation''' is a polarisation that is an isomorphism. Jacobians of curves are naturally equipped with a principal polarisation as soon as one picks an arbitrary rational base point on the curve, and the curve can be reconstructed from its polarised Jacobian when the genus is > 1. Not all principally polarised abelian varieties are Jacobians of curves; see the [[Schottky problem]]. A polarisation induces a [[Rosati involution]] on the [[endomorphism ring]] <math>\mathrm{End}(A)\otimes\mathbb{Q}</math> of ''A''. | |||
=== Polarisations over the complex numbers === | |||
Over the complex numbers, a '''polarised abelian variety''' can also be defined as an abelian variety ''A'' together with a choice of a Riemann form ''H''. Two Riemann forms ''H''<sub>1</sub> and ''H''<sub>2</sub> are called [[equivalence relation|equivalent]] if there are positive integers ''n'' and ''m'' such that ''nH''<sub>1</sub>=''mH''<sub>2</sub>. A choice of an equivalence class of Riemann forms on ''A'' is called a '''polarisation''' of ''A''. A morphism of polarised abelian varieties is a morphism ''A'' → ''B'' of abelian varieties such that the [[pullback (differential geometry)|pullback]] of the Riemann form on ''B'' to ''A'' is equivalent to the given form on ''A''. | |||
== Abelian scheme == | |||
One can also define abelian varieties [[scheme (mathematics)|scheme]]-theoretically and [[relative to a base]]. This allows for a uniform treatment of phenomena such as reduction mod ''p'' of abelian varieties (see [[Arithmetic of abelian varieties]]), and parameter-families of abelian varieties. An '''abelian scheme''' over a base scheme ''S'' of relative dimension ''g'' is a [[Proper morphism|proper]], [[smooth morphism|smooth]] [[group scheme]] over ''S'' whose [[geometric fiber]]s are [[connected space|connected]] and of dimension ''g''. The fibers of an abelian scheme are abelian varieties, so one could think of an abelian scheme over S as being a family of abelian varieties parametrised by S. | |||
==Semiabelian variety== | |||
A '''semiabelian variety''' is a commutative group variety which is an extension of an abelian variety by a [[Algebraic torus|torus]]. | |||
== See also == | |||
* [[Motive (algebraic geometry)|Motive]]s | |||
* [[Timeline of abelian varieties]] | |||
==References== | |||
* {{Citation | last1=Birkenhake | first1=Christina | last2=Lange | first2=H. | title=Complex Abelian varieties | publisher=[[Springer-Verlag]] | location=Berlin, New York | isbn=978-0-387-54747-3 | year=1992}}. A comprehensive treatment of the complex theory, with an overview of the history the subject. | |||
*{{eom|id=Abelian_scheme|authorlink=I. Dolgachev|first=I.V.|last=Dolgachev|title=Abelian scheme}} | |||
*{{Citation | |||
| last = Faltings | |||
| first = Gerd | |||
| authorlink = Gerd Faltings | |||
| coauthors = Chai, Ching-Li | |||
| title = Degeneration of Abelian Varieties | |||
| publisher = [[Springer Verlag]] | |||
| year = 1990 | |||
| pages = | |||
| url = | |||
| doi = | |||
| isbn =3-540-52015-5 }} | |||
* {{Citation | last1=Milne | first1=James | url=http://www.jmilne.org/math/CourseNotes/av.html | title=Abelian Varieties | accessdate=2007}}. Online course notes. | |||
* {{Citation | last1=Mumford | first1=David | author1-link=David Mumford | title=Abelian varieties | origyear=1970 | publisher=[[American Mathematical Society]] | location=Providence, R.I. | series=Tata Institute of Fundamental Research Studies in Mathematics | isbn=978-81-85931-86-9 | oclc=138290 | year=2008 | volume=5 | mr=0282985}} | |||
*{{eom|id=Abelian_variety|first=B.B.|last= Venkov|first2=A.N.|last2= Parshin|title=Abelian_variety}} | |||
* {{Citation | last1=Weil | first1=André | author1-link = André Weil | title=Variétés abéliennes et courbes algébriques | publisher=Hermann | location=Paris | oclc=826112 | year=1948}}. The first modern text on abelian varieties. In French. | |||
[[Category:Abelian varieties|*]] | |||
[[Category:Algebraic curves]] | |||
[[Category:Geometry of divisors]] | |||
[[Category:Algebraic surfaces]] | |||
[[Category:Niels Henrik Abel]] |
Revision as of 02:18, 2 February 2014
Template:No footnotes Template:Group theory sidebar
In mathematics, particularly in algebraic geometry, complex analysis and number theory, an abelian variety is a projective algebraic variety that is also an algebraic group, i.e., has a group law that can be defined by regular functions. Abelian varieties are at the same time among the most studied objects in algebraic geometry and indispensable tools for much research on other topics in algebraic geometry and number theory.
An abelian variety can be defined by equations having coefficients in any field; the variety is then said to be defined over that field. Historically the first abelian varieties to be studied were those defined over the field of complex numbers. Such abelian varieties turn out to be exactly those complex tori that can be embedded into a complex projective space. Abelian varieties defined over algebraic number fields are a special case, which is important also from the viewpoint of number theory. Localization techniques lead naturally from abelian varieties defined over number fields to ones defined over finite fields and various local fields.
Abelian varieties appear naturally as Jacobian varieties (the connected components of zero in Picard varieties) and Albanese varieties of other algebraic varieties. The group law of an abelian variety is necessarily commutative and the variety is non-singular. An elliptic curve is an abelian variety of dimension 1. Abelian varieties have Kodaira dimension 0.
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In the early nineteenth century, the theory of elliptic functions succeeded in giving a basis for the theory of elliptic integrals, and this left open an obvious avenue of research. The standard forms for elliptic integrals involved the square roots of cubic and quartic polynomials. When those were replaced by polynomials of higher degree, say quintics, what would happen?
In the work of Niels Abel and Carl Jacobi, the answer was formulated: this would involve functions of two complex variables, having four independent periods (i.e. period vectors). This gave the first glimpse of an abelian variety of dimension 2 (an abelian surface): what would now be called the Jacobian of a hyperelliptic curve of genus 2.
After Abel and Jacobi, some of the most important contributors to the theory of abelian functions were Riemann, Weierstrass, Frobenius, Poincaré and Picard. The subject was very popular at the time, already having a large literature.
By the end of the 19th century, mathematicians had begun to use geometric methods in the study of abelian functions. Eventually, in the 1920s, Lefschetz laid the basis for the study of abelian functions in terms of complex tori. He also appears to be the first to use the name "abelian variety". It was André Weil in the 1940s who gave the subject its modern foundations in the language of algebraic geometry.
Today, abelian varieties form an important tool in number theory, in dynamical systems (more specifically in the study of Hamiltonian systems), and in algebraic geometry (especially Picard varieties and Albanese varieties).
Analytic theory
Definition
A complex torus of dimension g is a torus of real dimension 2g that carries the structure of a complex manifold. It can always be obtained as the quotient of a g-dimensional complex vector space by a lattice of rank 2g. A complex abelian variety of dimension g is a complex torus of dimension g that is also a projective algebraic variety over the field of complex numbers. Since they are complex tori, abelian varieties carry the structure of a group. A morphism of abelian varieties is a morphism of the underlying algebraic varieties that preserves the identity element for the group structure. An isogeny is a finite-to-one morphism.
When a complex torus carries the structure of an algebraic variety, this structure is necessarily unique. In the case g = 1, the notion of abelian variety is the same as that of elliptic curve, and every complex torus gives rise to such a curve; for g > 1 it has been known since Riemann that the algebraic variety condition imposes extra constraints on a complex torus.
Riemann conditions
The following criterion by Riemann decides whether or not a given complex torus is an abelian variety, i.e. whether or not it can be embedded into a projective space. Let X be a g-dimensional torus given as X = V/L where V is a complex vector space of dimension g and L is a lattice in V. Then X is an abelian variety if and only if there exists a positive definite hermitian form on V whose imaginary part takes integral values on L×L. Such a form on X is usually called a (non-degenerate) Riemann form. Choosing a basis for V and L, one can make this condition more explicit. There are several equivalent formulations of this; all of them are known as the Riemann conditions.
The Jacobian of an algebraic curve
Every algebraic curve C of genus g ≥ 1 is associated with an abelian variety J of dimension g, by means of an analytic map of C into J. As a torus, J carries a commutative group structure, and the image of C generates J as a group. More accurately, J is covered by Cg: any point in J comes from a g-tuple of points in C. The study of differential forms on C, which give rise to the abelian integrals with which the theory started, can be derived from the simpler, translation-invariant theory of differentials on J. The abelian variety J is called the Jacobian variety of C, for any non-singular curve C over the complex numbers. From the point of view of birational geometry, its function field is the fixed field of the symmetric group on g letters acting on the function field of Cg.
Abelian functions
An abelian function is a meromorphic function on an abelian variety, which may be regarded therefore as a periodic function of n complex variables, having 2n independent periods; equivalently, it is a function in the function field of an abelian variety. For example, in the nineteenth century there was much interest in hyperelliptic integrals that may be expressed in terms of elliptic integrals. This comes down to asking that J is a product of elliptic curves, up to an isogeny.
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Algebraic definition
Two equivalent definitions of abelian variety over a general field k are commonly in use:
- a connected and complete algebraic group over k
- a connected and projective algebraic group over k.
When the base is the field of complex numbers, these notions coincide with the previous definition. Over all bases, elliptic curves are abelian varieties of dimension 1.
In the early 1940s, Weil used the first definition (over an arbitrary base field) but could not at first prove that it implied the second. Only in 1948 did he prove that complete algebraic groups can be embedded into projective space. Meanwhile, in order to make the proof of the Riemann hypothesis for curves over finite fields that he had announced in 1940 work, he had to introduce the notion of an abstract variety and to rewrite the foundations of algebraic geometry to work with varieties without projective embeddings (see also the history section in the Algebraic Geometry article).
Structure of the group of points
By the definitions, an abelian variety is a group variety. Its group of points can be proven to be commutative.
For C, and hence by the Lefschetz principle for every algebraically closed field of characteristic zero, the torsion group of an abelian variety of dimension g is isomorphic to (Q/Z)2g. Hence, its n-torsion part is isomorphic to (Z/nZ)2g, i.e. the product of 2g copies of the cyclic group of order n.
When the base field is an algebraically closed field of characteristic p, the n-torsion is still isomorphic to (Z/nZ)2g when n and p are coprime. When n and p are not coprime, the same result can be recovered provided one interprets it as saying that the n-torsion defines a finite flat group scheme of rank 2g. If instead of looking at the full scheme structure on the n-torsion, one considers only the geometric points, one obtains a new invariant for varieties in characteristic p (the so-called p-rank when n = p).
The group of k-rational points for a global field k is finitely generated by the Mordell-Weil theorem. Hence, by the structure theorem for finitely generated abelian groups, it is isomorphic to a product of a free abelian group Zr and a finite commutative group for some non-negative integer r called the rank of the abelian variety. Similar results hold for some other classes of fields k.
Products
The product of an abelian variety A of dimension m, and an abelian variety B of dimension n, over the same field, is an abelian variety of dimension m + n. An abelian variety is simple if it is not isogenous to a product of abelian varieties of lower dimension. Any abelian variety is isogenous to a product of simple abelian varieties.
Polarisation and dual abelian variety
Dual abelian variety
Mining Engineer (Excluding Oil ) Truman from Alma, loves to spend time knotting, largest property developers in singapore developers in singapore and stamp collecting. Recently had a family visit to Urnes Stave Church. To an abelian variety A over a field k, one associates a dual abelian variety Av (over the same field), which is the solution to the following moduli problem. A family of degree 0 line bundles parametrised by a k-variety T is defined to be a line bundle L on A×T such that
- for all t in T, the restriction of L to A×{t} is a degree 0 line bundle,
- the restriction of L to {0}×T is a trivial line bundle (here 0 is the identity of A).
Then there is a variety Av and a family of degree 0 line bundles P, the Poincaré bundle, parametrised by Av such that a family L on T is associated a unique morphism f: T → Av so that L is isomorphic to the pullback of P along the morphism 1A×f: A×T → A×Av. Applying this to the case when T is a point, we see that the points of Av correspond to line bundles of degree 0 on A, so there is a natural group operation on Av given by tensor product of line bundles, which makes it into an abelian variety.
This association is a duality in the sense that there is a natural isomorphism between the double dual Avv and A (defined via the Poincaré bundle) and that it is contravariant functorial, i.e. it associates to all morphisms f: A → B dual morphisms fv: Bv → Av in a compatible way. The n-torsion of an abelian variety and the n-torsion of its dual are dual to each other when n is coprime to the characteristic of the base. In general - for all n - the n-torsion group schemes of dual abelian varieties are Cartier duals of each other. This generalises the Weil pairing for elliptic curves.
Polarisations
A polarisation of an abelian variety is an isogeny from an abelian variety to its dual that is symmetric with respect to double-duality for abelian varieties and for which the pullback of the Poincaré bundle along the associated graph morphism is ample (so it is analogous to a positive-definite quadratic form). Polarised abelian varieties have finite automorphism groups. A principal polarisation is a polarisation that is an isomorphism. Jacobians of curves are naturally equipped with a principal polarisation as soon as one picks an arbitrary rational base point on the curve, and the curve can be reconstructed from its polarised Jacobian when the genus is > 1. Not all principally polarised abelian varieties are Jacobians of curves; see the Schottky problem. A polarisation induces a Rosati involution on the endomorphism ring of A.
Polarisations over the complex numbers
Over the complex numbers, a polarised abelian variety can also be defined as an abelian variety A together with a choice of a Riemann form H. Two Riemann forms H1 and H2 are called equivalent if there are positive integers n and m such that nH1=mH2. A choice of an equivalence class of Riemann forms on A is called a polarisation of A. A morphism of polarised abelian varieties is a morphism A → B of abelian varieties such that the pullback of the Riemann form on B to A is equivalent to the given form on A.
Abelian scheme
One can also define abelian varieties scheme-theoretically and relative to a base. This allows for a uniform treatment of phenomena such as reduction mod p of abelian varieties (see Arithmetic of abelian varieties), and parameter-families of abelian varieties. An abelian scheme over a base scheme S of relative dimension g is a proper, smooth group scheme over S whose geometric fibers are connected and of dimension g. The fibers of an abelian scheme are abelian varieties, so one could think of an abelian scheme over S as being a family of abelian varieties parametrised by S.
Semiabelian variety
A semiabelian variety is a commutative group variety which is an extension of an abelian variety by a torus.
See also
References
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010. A comprehensive treatment of the complex theory, with an overview of the history the subject. - Template:Eom
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010. Online course notes. - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Template:Eom
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010. The first modern text on abelian varieties. In French.