2
$\begingroup$

As we know, the albanese map $Alb$ assoicates a smooth proper variety $X$ of dimension $n$ to an abelian variety $Alb(X)$ of dimension $g=H^0(X,\Omega^1_X)$. Another well known fact is the moduli spaces $A_g$, $g\leq 3$ have dense subsets consisting of $Alb(X)$ for those $X$ satisfying $n=1$, which is no longer true for $g>3$. My questions are

  1. for $g>3$, could one always find $n$ < $g$, s.t. $A_g$ contains a dense subset consisting of $Alb(X)$, where $X$ satisfies dim $X\leq n$ and $g=H^0(X,\Omega^1_X)$.

  2. could anyong give explicitly a lower bound of such $n$ for some $g>3$

$\endgroup$

1 Answer 1

3
$\begingroup$

One can always take $n=2$ and this is the best possible:

Given a principally polarised abelian variety $(A, \Theta)$ of dimension $g$, if $S$ is the intersection of $g-2$ general elements of the linear system $|3\Theta|$, then $S$ is a smooth surface. The Lefschetz hyperplane section theorem implies that the natural map $H_1(S, \mathbb{Z}) \to H_1(A, \mathbb{Z})$ is an isomorphism which in turn implies that $Alb(S) \to A$ is an isomorphism.

(In the above I work over $\mathbb{C}$ but the conclusion holds over any infinite field; for finite fields one might have to replace $3$ by a larger integer.)

$\endgroup$
1
  • $\begingroup$ By your construction, one indeed realizes every polarized abelian varity as an albanese of an algebraic surface. Thanks a lot. $\endgroup$
    – gummi
    Commented Sep 19, 2011 at 15:11

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .