Fanography

A tool to visually study the geography of Fano 3-folds.

Identification

Fano variety 3-13

blowup of 2-32 in a curve $C$ of bidegree $(2,2)$ such that the composition $C\hookrightarrow W\hookrightarrow\mathbb{P}^2\times\mathbb{P}^2\overset{p_i}{\to}\mathbb{P}^2$ is an embedding for $i=1,2$

Picard rank
3 (others)
$-\mathrm{K}_X^3$
30
$\mathrm{h}^{1,2}(X)$
0
Hodge diamond and polyvector parallelogram
1
0 0
0 3 0
0 0 0 0
0 3 0
0 0
1
1
0 1*
0 1* 9
0 0 0 18
0 0 0
0 0
0
* indicates jumping of $\operatorname{Aut}^0$
its dimension takes on the values 1, 3
Anticanonical bundle
index
1
$\dim\mathrm{H}^0(X,\omega_X^\vee)$
18
$-\mathrm{K}_X$ very ample?
yes
$-\mathrm{K}_X$ basepoint free?
yes
hyperelliptic
no
trigonal
no
Birational geometry

This variety is rational.


This variety is the blowup of

  • 2-32, in a curve of genus 0

This variety is fibre-like, i.e. it can appear as the fibre of a Mori fibre space.

Deformation theory
number of moduli
1
Bott vanishing
does not hold
$\mathrm{Aut}^0(X)$ $\dim\mathrm{Aut}^0(X)$ number of moduli
$\mathrm{PGL}_2$ 3 0
$\mathbb{G}_{\mathrm{a}}$ 1 0
$\mathbb{G}_{\mathrm{m}}$ 1 1
Period sequence

The following period sequences are associated to this Fano 3-fold:

GRDB
#70
Fanosearch
#16
Extremal contractions
Semiorthogonal decompositions

A full exceptional collection can be constructed using Orlov's blowup formula.

Structure of quantum cohomology
Zero section description

Fano 3-folds from homogeneous vector bundles over Grassmannians gives the following description(s):

variety
$(\mathbb{P}^2)^3$
bundle
$\mathcal{O}(1,1,0) \oplus \mathcal{O}(1,0,1) \oplus \mathcal{O}(0,1,1)$

See the big table for more information.

Hilbert schemes of curves

The Hilbert scheme of conics is the disjoint union of 3 projective planes.

Its Hodge diamond is

1
0 0
0 1 0
0 0
1