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An algebraic surface is an algebraic variety of dimension two. In the case of geometry over the field of complex numbers, an algebraic surface has complex dimension two (as a complex manifold, when it is non-singular) and so of dimension four as a smooth manifold.

3 votes
Accepted

On surfaces with $p_g=0$, $q=1$, and $K^2=-3$

Xiao Gang is taking a configuration of six lines in the plane with 4 triple points $x,z_1,z_2,z_3$ and three double points $y_1,y_2,y_3$. He considers a general quartic through the seven points which …
Roberto Pignatelli's user avatar
3 votes

Torsion of the Picard group for surfaces isogenous to a product

I think the answer to the question as it is stated is negative: if I do understand correctly the question I can prove that, if $G$ is abelian and both curves $C_i/G$ are rational, this is never true …
Roberto Pignatelli's user avatar
1 vote
Accepted

Relation between curves in a complete linear system contained in another

In the following I suppose that by "curve" in a linear system you mean "effective divisor" vithout any claim about being irreducible and/or reduced. 1) Curves in |L'| are exactly the pull-back of cur …
Roberto Pignatelli's user avatar
4 votes

Isotrivial fibrations over $\mathbb P^1$

If the genus of the fibre is not 0, by Theorem 2.1 in Serrano's paper "Fibrations on algebraic surfaces" any isotrivial fibration is birational to $(A \times B)/G \rightarrow B/G$ where $G$ is a finit …
Roberto Pignatelli's user avatar
2 votes

Disjoint curves in an algebraic surface

The answer is clearly affirmative for $b=1$, which unfortunately corresponds only to 101 surfaces, including ${\mathbb P}^2$. I doubt that there is a single other case in which it works. Indeed I do …
Roberto Pignatelli's user avatar
2 votes
Accepted

Is each rationally chain connected surface rational?

By the comments of abx you only need an answer to question $3$. You get easily an answer if you assume the results in the classical book of Beauville on algebraic surfaces. Namely, if $S$ is uniruled …
Roberto Pignatelli's user avatar
5 votes
0 answers
335 views

Deformations of a blow up

My question is related to this question, but I'm looking for something a bit more explicit. Let $S$ be a smooth surface over $\mathbb C$, fix a point $s\in S$ and take the blow up $\beta \colon S' \r …
Roberto Pignatelli's user avatar
5 votes
Accepted

Does $h^1(D)=0$ imply numerical connectedness on K3 surfaces?

Interesting question. I think the answer is yes, let me try to prove it. As you noticed, the ideal sheaf sequence shows that $h^1(D)=0$ is equivalent to the fact that $H^0({\mathcal O}_D)$ is 1-dimen …
Roberto Pignatelli's user avatar
2 votes

Classification of quartic surfaces

A fine classification of the quartic surfaces that are not normal is in Tohsuke URABE, "Classification of Non-normal Quartic Surfaces", TOKYO J. MATH. VOL. 9, No. 2, 1986, 265-295
Roberto Pignatelli's user avatar