Fanography

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

Identification

Fano variety 3-12

blowup of 1-17 in the disjoint union of a line and a twisted cubic

Picard rank
3 (others)
$-\mathrm{K}_X^3$
28
$\mathrm{h}^{1,2}(X)$
0
Hodge diamond and polyvector parallelogram
1
0 0
0 3 0
0 0 0 0
0 3 0
0 0
1
1
0 0*
0 1* 7
0 0 0 17
0 0 0
0 0
0
* indicates jumping of $\operatorname{Aut}^0$
its dimension takes on the values 0, 1
Anticanonical bundle
index
1
$\dim\mathrm{H}^0(X,\omega_X^\vee)$
17
$-\mathrm{K}_X$ 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

  • 2-27, in a curve of genus 0
  • 2-33, in a curve of genus 0
  • 2-34, in a curve of genus 0
Deformation theory
number of moduli
1
Bott vanishing
does not hold
$\mathrm{Aut}^0(X)$ $\dim\mathrm{Aut}^0(X)$ number of moduli
$\mathbb{G}_{\mathrm{m}}$ 1 0
$0$ 0 1
Period sequence

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

GRDB
#85
Fanosearch
#144
Extremal contractions
Semiorthogonal decompositions

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

Structure of quantum cohomology

Generic semisimplicity of:

  • small quantum cohomology, proved by Ciolli in 2005, see [MR2168069] , using the description of a 1 or 2-curve blowup of $\mathbb{P}^3$ or $Q^3$
Zero section description

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

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

See the big table for more information.