Fanography

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

Identification

Fano variety 1-5: Gushel–Mukai 3-fold
  1. section of Plücker embedding of $\mathrm{Gr}(2,5)$ by codimension 2 subspace and a quadric
  2. double cover of 1-15 with branch locus an anticanonical divisor
Picard rank
1 (others)
$-\mathrm{K}_X^3$
10
$\mathrm{h}^{1,2}(X)$
10
Mori–Mukai $d$
10
Hodge diamond and polyvector parallelogram
1
0 0
0 1 0
0 10 10 0
0 1 0
0 0
1
1
0 0
0 22 0
0 0 0 8
0 1 0
0 0
0
Poisson structures

No nontrivial holomorphic Poisson structures.

See Loray–Pereira–Touzet.

Anticanonical bundle
index
1
$\dim\mathrm{H}^0(X,\omega_X^\vee)$
8
$-\mathrm{K}_X$ very ample?
yes if (a), else no
$-\mathrm{K}_X$ basepoint free?
yes
hyperelliptic
no
trigonal
no
Birational geometry

This variety is generally not rational.

A very general member is not stably rational.

The Weyl group associated to the KKMR decomposition is $\{e\}$; see the Weyl-group table for sources and conventions.


This variety is primitive.


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

Deformation theory
number of moduli
  1. 22
  2. 19
Bott vanishing
does not hold
$\mathrm{Aut}^0(X)$$\dim\mathrm{Aut}^0(X)$number of moduli
$0$022
Period sequence

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

GRDB
#160
Fanosearch
#9
Semiorthogonal decompositions

The naive atomic decomposition has atom dimensions $2+1+1$.

A standard semiorthogonal decomposition is $\langle \operatorname{Ku}(X), \mathcal{E}_2, \mathcal{O}_X \rangle$.

Both decompositions are recorded in Böhning–Graf von Bothmer–Su'a.

Structure of quantum cohomology

By Hertling–Manin–Teleman we have that quantum cohomology cannot be generically semisimple, as $\mathrm{h}^{1,2}\neq 0$.

Zero section description

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

variety
$\operatorname{Gr}(2,5)$
bundle
$\mathcal{O}(2) \oplus \mathcal{O}(1)^{\oplus2}$

See the big table for more information.

K-stability
  • every member is K‑stable
  • every member is K‑polystable
  • every member is K‑semistable
Seeand the big table for more information.
Coregularity

For this deformation family, the general member has coregularity at most 1; some member has coregularity 0.

The generic and uniform statements are due to Avilov–Loginov–Przyjalkowski; the existence of a smooth member of coregularity zero in every family is due to Zhakupov.

See coregularity for terminology.

Futaki invariant

For every K-polystable member, the Futaki invariant vanishes identically on the entire Kähler cone.

This is the computation of Sektnan–Tipler.