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Abelian varieties are projective algebraic varieties endowed with an Abelian group structure. Over the complex numbers, they can be described as quotients of a vector space by a lattice of full rank. They are analogs in higher dimensions of elliptic curves, and play an important role in algebraic geometry and number theory.

1 vote

Endomorphism ring of the Jacobian of a generic smooth plane quartic

See https://arxiv.org/abs/math/0405156 where Del Pezzo surfaces of degree 2 are used, in order to construct plane quartics, whose jacobians have endomorphism ring $\mathbb{Z}$.
Yuri Zarhin's user avatar
  • 5,050
2 votes

Generalization of $j(E) \in \overline { \Bbb{Z}}$ to abelian varieties of arbitrary dimension

The integrality of $j(E)$ means that an elliptic curve $E$ over a number field has potential good reduction everywhere (Deuring). So, the following assertion may be viewed as a generalization of the …
Yuri Zarhin's user avatar
  • 5,050
9 votes
Accepted

Isomorphic endomorphism algebras implies isogenous (for abelian varieties over finite fields)?

Here is a counterexample to Proposition A provided by 8-dimensional abelian varieties $A_1$ and $A_2$ over a finite field $F_{p^2}$ where $p$ is any prime that is congruent to $1$ modulo $17$ (e.g., …
Yuri Zarhin's user avatar
  • 5,050
8 votes
Accepted

Weil pairing on abelian varieties and etale Chern classes

It seems that one of the pairings is the negative of the other (in char 0 this assertion is actually Lemma 2.6 of https://arxiv.org/pdf/1809.01440.pdf ).
Yuri Zarhin's user avatar
  • 5,050
3 votes
Accepted

Mumford-Tate groups of abelian surfaces

The list of of all possible Hodge (special Mumford-Tate) groups of complex abelian varieties up to dimension 4 (and for simple abelian varieties up to dimension 5) is contained in https://arxiv.org/pd …
Yuri Zarhin's user avatar
  • 5,050
10 votes
Accepted

Abelian variety with prescribed endomorphism ring

The answer to your Question 3 is YES with the ground field $\mathbb{Q}$. Here is a sketch of the proof. For each positive integer $q$ and a "parameter" $t$ (in char 0) consider the smooth projective …
Mikhail Borovoi's user avatar
10 votes
Accepted

Does every Shimura variety contain a generic point defined over a number field?

The Answer to Question 1 is YES. It follows from Serre's variant of Hilbert's irreducibility theorem (for infinite Galois extensions) combined with the Tate conjecture on homomorphisms of abelian vari …
Mikhail Borovoi's user avatar
7 votes

Abelian variety with prescribed endomorphism ring

The answer to your Question 1 is NO. See Th. 5.1 of my 2015 JPAA paper. The answer to your Question 2 is YES. See 1963 Annals paper of Shimura "On analytic families ..".
Mikhail Borovoi's user avatar
3 votes
Accepted

How to prove that $A$ is supersingular iff the Picard number $\rho(A)$ is equal to the secon...

Now let $k$ be a finite field. If $E$ is an elliptic curve over $k$ then $End(E)\otimes\mathbf{Q}$ is either an imaginary quadratic field or a definite quaternion algebra over $\mathbf{Q}$. Warnin …
Yuri Zarhin's user avatar
  • 5,050
4 votes

How to prove that $A$ is supersingular iff the Picard number $\rho(A)$ is equal to the secon...

If $A$ is not simple then it is isogenous to a product $E_1 \times E_2$ of elliptic curves $E_1$ and $E_2$, and the Picard numbers of $A$ and $E_1\times E_2$ do coincide. If $E_1$ is not isogenous to …
Yuri Zarhin's user avatar
  • 5,050
16 votes
Accepted

n-th root of unity in n-th division field of abelian variety?

Actually, this is an exercise in Serre's Lectures on Mordell--Weil Theorem: $K(A[n])$ always contains $\mu_n$ if $char(K)$ does not divide $n$ and $A$ is an abelian variety of positive dimension over …
Yuri Zarhin's user avatar
  • 5,050
7 votes

Endomorphism Ring of Simple Abelian Varieties

Albert's classification works/is good enough for (algebraically closed) fields of characteristic zero. For the complete list of all possibilities for a given $g$ (including the case of prime characte …
Yuri Zarhin's user avatar
  • 5,050
6 votes
Accepted

can all CM types be realized by Jacobians?

``Given $(K,\Phi)$ , there always exists a $g$ -dimensional abelian variety $A$ such that $End(A)\otimes Q=K$ and that $K$ acts on $H^0(A,\Omega^1)$ through $\Phi$. One easily constructs as a comp …
Yuri Zarhin's user avatar
  • 5,050
12 votes
Accepted

Tate conjecture for abelian varieties over a finitely generated extension of an algebraicall...

The answer is no: an easy (not interesting) counterexample is provided by "constant" abelian varieties, i.e., when $A$ and $B$ are defined over an algebraically closed field $k$ of characteristic zer …
Yuri Zarhin's user avatar
  • 5,050
5 votes

Theta group representation

If I understand correctly, $K_1$ and $K_2$ are (mutually orthogonal maximal) isotropic subgroups of $K(L)$. Therefore they both can be lifted (non-canonically) to (finite) commutative (sic!) subgrou …
Yuri Zarhin's user avatar
  • 5,050

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