\begin{equation} \DeclareMathOperator\Gr{Gr} \DeclareMathOperator\LGr{LGr} \DeclareMathOperator\OGr{OGr} \DeclareMathOperator\SGr{SGr} \DeclareMathOperator\Kzero{K_0} \DeclareMathOperator\index{i} \DeclareMathOperator\rk{rk} \end{equation}

Grassmannian.info

A periodic table of (generalised) Grassmannians.

Quadric $\mathrm{{Q}}^{{3}}$

Y Z Y Z
Betti numbers
\begin{align*} \mathrm{b}_{ 0 } &= 1 \\ \mathrm{b}_{ 2 } &= 1 \\ \mathrm{b}_{ 4 } &= 1 \\ \mathrm{b}_{ 6 } &= 1 \end{align*}
Basic information
dimension
3
index
3
Euler characteristic
4
Betti numbers
$\mathrm{b}_{ 0 } = 1$, $\mathrm{b}_{ 2 } = 1$, $\mathrm{b}_{ 4 } = 1$, $\mathrm{b}_{ 6 } = 1$
$\mathrm{Aut}^0(\mathrm{{Q}}^{{3}})$
$\mathrm{PSp}_{ 4 }$
$\pi_0\mathrm{Aut}(\mathrm{{Q}}^{{3}})$
$1$
$\dim\mathrm{Aut}^0(\mathrm{{Q}}^{{3}})$
10
Projective geometry
minimal embedding

$\mathrm{{Q}}^{{3}}\hookrightarrow\mathbb{P}^{ 4 }$

degree
2
Hilbert series
1, 5, 14, 30, 55, 91, 140, 204, 285, 385, 506, 650, 819, 1015, 1240, 1496, 1785, 2109, 2470, 2870, ...
Projective duality

A smooth quadric in the dual projective space.

codimension
1
degree
2
self-dual
yes

[Tevelev, Theorems 9.19 and 10.22 (arXiv version)] All Grassmannians.

Exceptional collections

Full exceptional collections in $\mathbf D^{\mathrm b}(\mathrm{{Q}}^{{3}})$:

Quantum cohomology
small
generically semisimple [Chaput–Manivel–Perrin]

Minuscule/cominuscule case, including quadric realisations.

big
generically semisimple [Li–Liu–Yu–Zhang, Theorems 1.2 and 1.4]

Convergent near the large-radius limit.

Earlier proof for coadjoint varieties: [Perrin–Smirnov] .

Eigenvalues of quantum multiplication by $\mathrm{c}_1(\mathrm{{Q}}^{{3}})$:

Homological projective duality

Full minimal nonrectangular Lefschetz collection. [Kuznetsov–Perry, Lemma 2.4]

Lefschetz block sizes: 2, 1, 1

Block sizes $(2, 1, 1)$; 4 objects.

Lefschetz centre: a spinor bundle and the structure sheaf.

HP dual: the double cover of the dual projective space branched over the dual quadric, for the spinor Lefschetz structure. [Kuznetsov–Perry, Theorem 1.1]

$k$-Fanoness

2-Fano: $\mathrm{ch}_i(\mathrm{T}_{ \mathrm{{Q}}^{{3}} })\cdot Z>0$ for every nonzero effective $i$-dimensional cycle $Z$ and $1\leq i\leq 2$. [Araujo et al., Theorems 1.3 and 1.4]

References
  1. Kuznetsov, Alexander. Exceptional collections for Grassmannians of isotropic lines. Proc. Lond. Math. Soc. (3) 97 (2008), 155–182. MR2434094.
  2. Pierre-Emmanuel Chaput; Laurent Manivel; Nicolas Perrin. Quantum cohomology of minuscule homogeneous spaces III : semi-simplicity and consequences. Canad. J. Math. 62 (2010), 1246–1263. arXiv:0710.1224.
  3. Alexander Kuznetsov; Alexander Perry. Homological projective duality for quadrics. J. Algebraic Geom. 30 (2021), 457–476. arXiv:1902.09832.
  4. Carolina Araujo; Roya Beheshti; Ana-Maria Castravet; Kelly Jabbusch; Svetlana Makarova; Enrica Mazzon; Libby Taylor; Nivedita Viswanathan. Higher Fano Manifolds. Rev. Un. Mat. Argentina 64 (2022), 103–125. arXiv:2110.02339.
  5. Anton Fonarev. Full exceptional collections on Lagrangian Grassmannians. Int. Math. Res. Not. 2022 (2), 1081–1122. arXiv:1911.08968.
  6. Alexander Samokhin; Wilberd van der Kallen. Highest weight category structures on $\operatorname{rep}(B)$ and full exceptional collections on generalized flag varieties over $\mathbb Z$. Preprint (2024). arXiv:2407.13653.
  7. Nicolas Perrin; Maxim Smirnov. On the big quantum cohomology of coadjoint varieties. Selecta Math. 31 (2025), article 30. arXiv:2112.12436.
  8. Lyalya Guseva; Alexander Novikov. Full exceptional collections on the symplectic isotropic Grassmannians. Advances in Mathematics (2026), article 111211. arXiv:2505.13005.
  9. Changzheng Li; Zhaoyang Liu; Tony Yue Yu; Chi Zhang. Convergence and semisimplicity of big quantum cohomology of flag varieties. Preprint (2026). arXiv:2610.28418.

All references.