Description of Fano 3-folds as zero loci in a product of (weighted) Grassmannians
In Fano 3-folds from homogeneous vector bundles over Grassmannians De Biase–Fatighenti–Tanturri obtained a description of a general member of each deformation family of Fano 3-folds as the zero locus of a homogeneous vector bundle in a product of Grassmannians and weighted projective spaces. Such description gives new tools to compute cohomological invariants of Fano 3-folds (by virtue of the Borel–Weil–Bott theorem), and gives a representation-theoretic flavour to the classification.
Some of these descriptions are classical (and in fact agree with the usual description of the Fano 3-folds), others were obtained for the Fanosearch project in Quantum periods for 3-dimensional Fano manifolds by Coates–Corti–Galkin–Kasprzyk. In the table below we list the description of De Biase–Fatighenti–Tanturri, using their notation.
ID | description | ambient variety | homogeneous vector bundle | origin |
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1-1 |
double cover of $\mathbb{P}^3$ with branch locus a divisor of degree 6
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1-2 |
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$\mathbb{P}^4$ | $\mathcal{O}(4)$ | classical |
1-3 |
complete intersection of quadric and cubic in $\mathbb{P}^5$ |
$\mathbb{P}^5$ | $\mathcal{O}(2) \oplus \mathcal{O}(3)$ | classical |
1-4 |
complete intersection of 3 quadrics in $\mathbb{P}^6$ |
$\mathbb{P}^6$ | $\mathcal{O}(2)^{\oplus 3}$ | classical |
1-5 |
Gushel–Mukai 3-fold
|
$\operatorname{Gr}(2,5)$ | $\mathcal{O}(2) \oplus \mathcal{O}(1)^{\oplus2}$ | classical |
1-6 |
section of half-spinor embedding of a connected component of $\mathrm{OGr}_+(5,10)$ by codimension 7 subspace |
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1-7 |
section of Plücker embedding of $\mathrm{Gr}(2,6)$ by codimension 5 subspace |
$\operatorname{Gr}(2,6)$ | $\mathcal{O}(1)^{\oplus5}$ | classical |
1-8 |
section of Plücker embedding of $\mathrm{SGr}(3,6)$ by codimension 3 subspace |
$\operatorname{Gr}(3,6)$ | $\bigwedge^2\mathcal{U}^{\vee} \oplus \mathcal{O}(1)^{\oplus3}$ | classical |
1-9 |
section of the adjoint $\mathrm{G}_2$-Grassmannian $\mathrm{G}_2\mathrm{Gr}(2,7)$ by codimension 2 subspace |
$\operatorname{Gr}(2,7)$ | $\mathcal{Q}^{\vee}(1) \oplus \mathcal{O}(1)^{\oplus2}$ | classical |
1-10 |
zero locus of $(\bigwedge^2\mathcal{U}^\vee)^{\oplus 3}$ on $\mathrm{Gr}(3,7)$ |
$\operatorname{Gr}(3,7)$ | $(\bigwedge^2\mathcal{U}^\vee)^{\oplus 3}$ | classical |
1-11 |
hypersurface of degree 6 in $\mathbb{P}(1,1,1,2,3)$ |
$\mathbb{P}(1^3,2,3)$ | $\mathcal{O}(6)$ | classical |
1-12 |
double cover of $\mathbb{P}^3$ with branch locus a smooth quartic surface
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1-13 |
hypersurface of degree 3 in $\mathbb{P}^4$ |
$\mathbb{P}^4$ | $\mathcal{O}(3)$ | classical |
1-14 |
complete intersection of 2 quadrics in $\mathbb{P}^5$ |
$\mathbb{P}^5$ | $\mathcal{O}(2)^{\oplus 2}$ | classical |
1-15 |
section of Plücker embedding of $\mathrm{Gr}(2,5)$ by codimension 3 subspace |
$\operatorname{Gr}(2,5)$ | $\mathcal{O}(1)^{\oplus 3}$ | classical |
1-16 |
hypersurface of degree 2 in $\mathbb{P}^4$ |
$\mathbb{P}^4$ | $\mathcal{O}(2)$ | classical |
1-17 |
projective space $\mathbb{P}^3$ |
$\mathbb{P}^3$ | classical | |
2-1 |
blowup of 1-11 in an elliptic curve which is the intersection of two divisors from half the anticanonical linear system |
$\mathbb{P}(1^3,2,3) \times \mathbb{P}^1$ | $\mathcal{O}(6,0) \oplus \mathcal{O}(1,1)$ | [CCGK] |
2-2 |
double cover of 2-34 with branch locus a $(2,4)$-divisor |
$\mathbb{P}^1\times \mathbb{P}^2 \times \mathbb{P}^{12}$ |
$\mathcal{O}(0,0,2) \oplus K(0,0,1)$
$K \in \operatorname{Ext}_{\mathbb{P}^1 \times \mathbb{P}^2}^2(\mathcal{O}(1,0)^{\oplus 6}, \mathcal{Q}_{\mathbb{P}^2}(-1,-1))$ |
[DBFT] |
2-3 |
blowup of 1-12 in an elliptic curve which is the intersection of two divisors from half the anticanonical linear system |
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2-4 |
blowup of 1-17 in the intersection of two cubics
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$\mathbb{P}^1 \times \mathbb{P}^3$ | $\mathcal{O}(1,3)$ | [CCGK] |
2-5 |
blowup of 1-13 in a plane cubic |
$\mathbb{P}^1 \times \mathbb{P}^4$ | $\mathcal{O}(0,3) \oplus \mathcal{O}(1,1)$ | [DBFT] |
2-6 |
Verra 3-fold
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$\mathbb{P}^2 \times \mathbb{P}^2$ | $\mathcal{O}(2,2)$ | [CCGK] |
2-7 |
blowup of 1-16 in the intersection of two divisors from $|\mathcal{O}_Q(2)|$ |
$\mathbb{P}^1 \times \mathbb{P}^4$ | $\mathcal{O}(0,2) \oplus \mathcal{O}(1,2)$ | [CCGK] |
2-8 | $\mathbb{P}^2 \times \mathbb{P}^3 \times \mathbb{P}^{12}$ |
$\Lambda(0,0,1) \oplus \mathcal{O}(0,0,2)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^2 \times \mathbb{P}^3}(\mathcal{Q}_{\mathbb{P}^3}^{\oplus 3}, \mathcal{Q}_{\mathbb{P}^2}(0, -1))$ |
[DBFT] | |
2-9 |
complete intersection of degree $(1,1)$ and $(2,1)$ in $\mathbb{P}^3\times\mathbb{P}^2$
|
$\mathbb{P}^2 \times \mathbb{P}^3$ | $\mathcal{O}(1,1) \oplus \mathcal{O}(1,2)$ | [CCGK] |
2-10 |
blowup of 1-14 in an elliptic curve which is an intersection of 2 hyperplanes |
$\operatorname{Gr}(2,4) \times \mathbb{P}^1$ | $\mathcal{O}(2,0) \oplus \mathcal{O}(1,1)$ | [DBFT] |
2-11 |
blowup of 1-13 in a line |
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2-12 |
intersection of 3 $(1,1)$-divisors in $\mathbb{P}^3\times\mathbb{P}^3$
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$\mathbb{P}^3 \times \mathbb{P}^3$ | $\mathcal{O}(1,1)^{\oplus 3}$ | [CCGK] |
2-13 |
blowup of 1-16 in a curve of degree 6 and genus 2 |
$\mathbb{P}^2 \times \mathbb{P}^4$ | $\mathcal{O}(1,1)^{\oplus 2} \oplus \mathcal{O}(0,2)$ | [CCGK] |
2-14 |
blowup of 1-15 in an elliptic curve which is an intersection of 2 hyperplanes |
$\operatorname{Gr}(2,5) \times \mathbb{P}^1$ | $\mathcal{O}(1,0)^{\oplus 3} \oplus \mathcal{O}(1,1)$ | [CCGK] |
2-15 |
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2-16 |
blowup of 1-14 in a conic |
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2-17 |
blowup of 1-16 in an elliptic curve of degree 5 |
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2-18 |
double cover of 2-34 with branch locus a divisor of degree $(2,2)$ |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^6$ |
$\Lambda(0,0,1) \oplus \mathcal{O}(0,0,2)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1 \times \mathbb{P}^2}(\mathcal{Q}_{\mathbb{P}^2}^{\oplus 2}, \mathcal{O}(1,-1))$ |
[DBFT] |
2-19 |
blowup of 1-14 in a line |
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2-20 |
blowup of 1-15 in a twisted cubic |
$\operatorname{Gr}(2,5) \times \mathbb{P}^2$ | $\mathcal{U}^{\vee}_{\operatorname{Gr}(2,5)}(0,1) \oplus \mathcal{O}(1,0)^{\oplus 3}$ | [CCGK] |
2-21 |
blowup of 1-16 in a twisted quartic |
$\operatorname{Gr}(2,4) \times \mathbb{P}^4$ | $\mathcal{U}^{\vee}_{\operatorname{Gr}(2,4)}(0,1)^{\oplus 2} \oplus \mathcal{O}(1,0)$ | [CCGK] |
2-22 |
blowup of 1-15 in a conic |
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2-23 |
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2-24 |
divisor on $\mathbb{P}^2\times\mathbb{P}^2$ of bidegree $(1,2)$ |
$\mathbb{P}^2 \times \mathbb{P}^2$ | $\mathcal{O}(1,2)$ | classical |
2-25 |
blowup of 1-17 in an elliptic curve which is an intersection of 2 quadrics
|
$\mathbb{P}^1 \times \mathbb{P}^3$ | $\mathcal{O}(1,2)$ | [CCGK] |
2-26 |
blowup of 1-15 in a line |
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2-27 |
blowup of 1-17 in a twisted cubic |
$\mathbb{P}^3 \times \mathbb{P}^2$ | $\mathcal{O}(1,1)^{\oplus 2}$ | [CCGK] |
2-28 |
blowup of 1-17 in a plane cubic |
$\mathbb{P}^3 \times \mathbb{P}^{10}$ |
$\Lambda(0,1) \oplus \mathcal{O}(1,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^3}(\operatorname{Sym}^2\mathcal{Q}, \mathcal{Q}(-1))$ |
[DBFT] |
2-29 |
blowup of 1-16 in a conic |
$\mathbb{P}^1 \times \mathbb{P}^4$ | $\mathcal{O}(0,2) \oplus \mathcal{O}(1,1)$ | [DBFT] |
2-30 |
blowup of 1-17 in a conic |
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2-31 |
blowup of 1-16 in a line |
$\mathbb{P}^2 \times \operatorname{Gr}(2,4)$ | $\mathcal{U}^{\vee}_{\operatorname{Gr}(2,4)}(1,0) \oplus \mathcal{O}(0,1)$ | [DBFT] |
2-32 |
divisor on $\mathbb{P}^2\times\mathbb{P}^2$ of bidegree $(1,1)$
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2-33 |
blowup of 1-17 in a line |
$\mathbb{P}^1 \times \mathbb{P}^3$ | $\mathcal{O}(1,1)$ | [DBFT] |
2-34 |
$\mathbb{P}^1\times\mathbb{P}^2$ |
$\mathbb{P}^1 \times \mathbb{P}^2$ | classical | |
2-35 |
$\mathrm{Bl}_p\mathbb{P}^3$
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2-36 |
$\mathbb{P}(\mathcal{O}_{\mathbb{P}^2}\oplus\mathcal{O}_{\mathbb{P}^2}(2))$ |
$\mathbb{P}^2 \times \mathbb{P}^6$ |
$\Lambda(0,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^2}(\operatorname{Sym}^2\mathcal{Q}, \mathcal{Q}(-1))$ |
[DBFT] |
3-1 |
double cover of 3-27 with branch locus a divisor of degree $(2,2,2)$ |
$\mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^8$ |
$K(0,0,0,1) \oplus \mathcal{O}(0,0,0,2)$
$K \in \operatorname{Ext}^2_{(\mathbb{P}^1)^3}(\mathcal{O}(0,0,1)^{\oplus 4},\mathcal{O}(1,-1,-1))$ |
[DBFT] |
3-2 |
divisor from $|\mathcal{L}^{\otimes 2}\otimes\mathcal{O}(2,3)|$ on the $\mathbb{P}^2$-bundle $\mathbb{P}(\mathcal{O}\oplus\mathcal{O}(-1,-1)^{\oplus 2})$ over $\mathbb{P}^1\times\mathbb{P}^1$ such that $X\cap Y$ is irreducible, and $\mathcal{L}$ is the tautological bundle, and $Y\in|\mathcal{L}|$ |
$\mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^5$ |
$\Lambda(0,0,1) \oplus \mathcal{O}(0,1,2)$
$\Lambda \in \operatorname{Ext}^1_{(\mathbb{P}^1)^2}(\mathcal{O}(0,1)^{\oplus 2}, \mathcal{O}(1, -1))$ |
[DBFT] |
3-3 |
divisor on $\mathbb{P}^1\times\mathbb{P}^1\times\mathbb{P}^2$ of degree $(1,1,2)$ |
$\mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^2$ | $\mathcal{O}(1,1,2)$ | [CCGK] |
3-4 |
blowup of 2-18 in a smooth fiber of the composition of the projection to $\mathbb{P}^1\times\mathbb{P}^2$ with the projection to $\mathbb{P}^2$ of the double cover with the projection |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^6 \times \mathbb{P}^1$ |
$\Lambda(0,0,1,0) \oplus \mathcal{O}(0,0,2,0) \oplus \mathcal{O}(0,1,0,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1 \times \mathbb{P}^2}(\mathcal{Q}_{\mathbb{P}^2}^{\oplus 2}, \mathcal{O}(1,-1))$ |
[DBFT] |
3-5 |
blowup of 2-34 in a curve $C$ of degree $(5,2)$ such that $C\hookrightarrow\mathbb{P}^1\times\mathbb{P}^2\to\mathbb{P}^2$ is an embedding |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^7$ |
$\Lambda(0,0,1) \oplus \mathcal{O}(0,1,1)^{\oplus 2}$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1 \times \mathbb{P}^2}(\mathcal{Q}_{\mathbb{P}^2}^{\oplus 2}, \mathcal{O}(1,-1))$ |
[DBFT] |
3-6 |
blowup of 1-17 in the disjoint union of a line and an elliptic curve of degree 4
|
$\mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^3$ | $\mathcal{O}(1,0,2) \oplus \mathcal{O}(0,1,1)$ | [DBFT] |
3-7 |
blowup of 2-32 in an elliptic curve which is the intersection of two divisors from $|-\frac{1}{2}\mathrm{K}_W|$ |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^2$ | $\mathcal{O}(0,1,1) \oplus \mathcal{O}(1,1,1)$ | [CCGK] |
3-8 |
divisor from the linear system $|(\alpha\circ\pi_1)^*(\mathcal{O}_{\mathbb{P}^2}(1)\otimes\pi_2^*(\mathcal{O}_{\mathbb{P}^2}(2))|$ where $\pi_i\colon\mathrm{Bl}_1\mathbb{P}^2\times\mathbb{P}^2\to\mathrm{Bl}_1\mathbb{P}^2,\mathbb{P}^2$ are the projections, and $\alpha\colon\mathrm{Bl}_1\mathbb{P}^2\to\mathbb{P}^2$ is the blowup |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^2$ | $\mathcal{O}(0,1,2) \oplus \mathcal{O}(1,1,0)$ | [DBFT] |
3-9 |
blowup of the cone over the Veronese of $\mathbb{P}^2$ in $\mathbb{P}^5$ with center the disjoint union of the vertex and a quartic curve on $\mathbb{P}^2$ |
$\mathbb{P}^2 \times \mathbb{P}^6 \times \mathbb{P}^{20}$ |
$\Lambda(0,1,0) \oplus \mathcal{Q}_{\mathbb{P}^6}(0,0,1) \oplus K(0,0,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^2}(\operatorname{Sym}^2\mathcal{Q}, \mathcal{Q}(-1))$, $K \in \operatorname{Ext}^3_{\mathbb{P}^2}(\operatorname{Sym}^4\mathcal{Q}, \mathcal{Q}(-3))$ |
[DBFT] |
3-10 |
blowup of 1-16 in the disjoint union of 2 conics
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$\mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^4$ | $\mathcal{O}(1,0,1) \oplus \mathcal{O}(0,1,1) \oplus \mathcal{O}(0,0,2)$ | [DBFT] |
3-11 |
blowup of 2-35 in an elliptic curve which is the intersection of two divisors from $|-\frac{1}{2}\mathrm{K}_{V_7}|$ |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^3$ | $\mathcal{O}(1,1,1) \oplus \mathcal{Q}_{\mathbb{P}^2}(0,0,1)$ | [DBFT] |
3-12 |
blowup of 1-17 in the disjoint union of a line and a twisted cubic |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^3$ | $\mathcal{O}(0,1,1) \oplus \mathcal{O}(0,1,1) \oplus \mathcal{O}(1,0,1)$ | [DBFT] |
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 $i=1,2$ |
$(\mathbb{P}^2)^3$ | $\mathcal{O}(1,1,0) \oplus \mathcal{O}(1,0,1) \oplus \mathcal{O}(0,1,1)$ | [CCGK] |
3-14 |
blowup of 1-17 in the disjoint union of a plane cubic curve and a point outside the plane |
$\mathbb{P}^3 \times \mathbb{P}^{10} \times \mathbb{P}^2$ |
$\Lambda(0,1,0) \oplus \mathcal{Q}_{\mathbb{P}^2}(1,0,0) \oplus \mathcal{O}(1,1,0)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^3}(\operatorname{Sym}^2\mathcal{Q}, \mathcal{Q}(-1)) $ |
[DBFT] |
3-15 |
blowup of 1-16 in the disjoint union of a line and a conic |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^4$ | $\mathcal{O}(1,0,1) \oplus \mathcal{O}(0,1,1) \oplus \mathcal{Q}_{\mathbb{P}^2}(0,0,1)$ | [DBFT] |
3-16 |
blowup of 2-35 in the proper transform of a twisted cubic containing the center of the blowup |
$\mathbb{P}^2_1 \times \mathbb{P}^2_2 \times \mathbb{P}^3$ | $\mathcal{O}(0,1,1) \oplus \mathcal{O}(1,1,0) \oplus \mathcal{Q}_{\mathbb{P}^2_1}(0,0,1)$ | [DBFT] |
3-17 |
divisor on $\mathbb{P}^1\times\mathbb{P}^1\times\mathbb{P}^2$ of degree $(1,1,1)$ |
$\mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^2$ | $\mathcal{O}(1,1,1)$ | [CCGK] |
3-18 |
blowup of 1-17 in the disjoint union of a line and a conic |
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3-19 |
blowup of 1-16 in two non-collinear points |
$\mathbb{P}^2 \times \mathbb{P}^4$ | $\mathcal{O}(0,2) \oplus \mathcal{Q}_{\mathbb{P}^2}(0,1)$ | [DBFT] |
3-20 |
blowup of 1-16 in the disjoint union of two lines |
$\mathbb{P}^2_1 \times \mathbb{P}^2_2 \times \mathbb{P}^4$ | $\mathcal{O}(1,1,0) \oplus \mathcal{Q}_{\mathbb{P}^2_1}(0,0,1) \oplus \mathcal{Q}_{\mathbb{P}^2_2}(0,0,1)$ | [DBFT] |
3-21 |
blowup of 2-34 in a curve of degree $(2,1)$ |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^6$ |
$\mathcal{O}(0,1,1) \oplus \Lambda(0,0,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1 \times \mathbb{P}^2}(\mathcal{Q}_{\mathbb{P}^2}^{\oplus 2}, \mathcal{O}(1,-1)) $ |
[DBFT] |
3-22 |
blowup of 2-34 in a conic on $\{x\}\times\mathbb{P}^2$, $x\in\mathbb{P}^1$ |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^6$ |
$\mathcal{O}(1,0,1) \oplus \Lambda(0,0,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^2}(\operatorname{Sym}^2 \mathcal{Q}, \mathcal{Q}(-1))$ |
[DBFT] |
3-23 |
blowup of 2-35 in the proper transform of a conic containing the center of the blowup |
$\mathbb{P}^2 \times \mathbb{P}^3 \times \mathbb{P}^4$ | $\mathcal{Q}_{\mathbb{P}^2}(0,1,0) \oplus \mathcal{O}(1,0,1) \oplus \mathcal{Q}_{\mathbb{P}^3}(0,0,1)$ | [DBFT] |
3-24 |
the fiber product of 2-32 with $\mathrm{Bl}_p\mathbb{P}^2$ over $\mathbb{P}^2$
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$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^2$ | $\mathcal{O}(1,1,0) \oplus \mathcal{O}(0,1,1)$ | [CCGK] |
3-25 |
blowup of 1-17 in the disjoint union of two lines
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3-26 |
blowup of 1-17 in the disjoint union of a point and a line
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$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^3$ | $\mathcal{O}(1,0,1) \oplus \mathcal{Q}_{\mathbb{P}^2}(0,0,1)$ | [DBFT] |
3-27 |
$\mathbb{P}^1\times\mathbb{P}^1\times\mathbb{P}^1$ |
$\mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^1$ | classical | |
3-28 |
$\mathbb{P}^1\times\mathrm{Bl}_p\mathbb{P}^2$ |
$\mathbb{P}^1 \times \mathbb{P}^1 \times \mathbb{P}^2$ | $\mathcal{O}(1,0,1)$ | [DBFT] |
3-29 |
blowup of 2-35 in a line on the exceptional divisor |
$\mathbb{P}^3 \times \mathbb{P}^2 \times \mathbb{P}^9$ |
$\mathcal{Q}_{\mathbb{P}^2}(1,0,0) \oplus \mathcal{Q}_{\mathbb{P}^3}(0,0,1) \oplus\Lambda(0,0,1) \oplus \mathcal{O}(0,-1,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^2}(\operatorname{Sym}^2\mathcal{Q}, \mathcal{Q}(-1))$ |
[DBFT] |
3-30 |
blowup of 2-35 in the proper transform of a line containing the center of the blowup
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$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^3$ | $\mathcal{O}(1,1,0) \oplus \mathcal{Q}_{\mathbb{P}^2}(0,0,1)$ | [DBFT] |
3-31 |
blowup of the cone over a smooth quadric in $\mathbb{P}^3$ in the vertex
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4-1 |
divisor on $\mathbb{P}^1\times\mathbb{P}^1\times\mathbb{P}^1\times\mathbb{P}^1$ of degree $(1,1,1,1)$ |
$(\mathbb{P}^1)^4$ | $\mathcal{O}(1,1,1,1)$ | classical |
4-2 |
blowup of the cone over a smooth quadric in $\mathbb{P}^3$ in the disjoint union of the vertex and an elliptic curve on the quadric |
$\mathbb{P}^3 \times \mathbb{P}^4 \times \mathbb{P}^5$ | $\mathcal{Q}_{\mathbb{P}^3}(0,1,0) \oplus \mathcal{Q}_{\mathbb{P}^4}(0,0,1) \oplus \mathcal{O}(2,0,0) \oplus \mathcal{O}(0,1,1)$ | [DBFT] |
4-3 |
blowup of 3-27 in a curve of degree $(1,1,2)$ |
$(\mathbb{P}^1)^3 \times \mathbb{P}^2$ | $\mathcal{O}(1,1,0,1) \oplus \mathcal{O}(0,0,1,1)$ | [DBFT] |
4-4 |
blowup of 3-19 in the proper transform of a conic through the points |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^4$ | $\mathcal{O}(1,1,0) \oplus \mathcal{O}(0,0,2) \oplus \mathcal{Q}_{\mathbb{P}^2}(0,0,1)$ | [DBFT] |
4-5 |
blowup of 2-34 in the disjoint union of a curve of degree $(2,1)$ and a curve of degree $(1,0)$ |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^6 \times \mathbb{P}^1$ |
$\mathcal{O}(0,1,1,0) \oplus \Lambda(0,0,1,0) \oplus \mathcal{O}(0,1,0,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1 \times \mathbb{P}^2}(\mathcal{Q}_{\mathbb{P}^2}^{\oplus 2},\mathcal{O}(1,-1))$ |
[DBFT] |
4-6 |
blowup of 1-17 in the disjoint union of 3 lines
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$(\mathbb{P}^1)^3 \times \mathbb{P}^3$ | $\mathcal{O}(1,0,0,1) \oplus \mathcal{O}(0,1,0,1) \oplus \mathcal{O}(0,0,1,1)$ | [DBFT] |
4-7 |
blowup of 2-32 in the disjoint union of a curve of degree $(0,1)$ and a curve of degree $(1,0)$ |
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4-8 |
blowup of 3-27 in a curve of degree $(0,1,1)$ |
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4-9 |
blowup of 3-25 in an exceptional curve of the blowup |
$(\mathbb{P}^1)^2 \times \mathbb{P}^2 \times \mathbb{P}^3$ | $\mathcal{O}(1,0,1,0) \oplus \mathcal{O}(0,1,0,1) \oplus \mathcal{Q}_{\mathbb{P}^2}(0,0,0,1)$ | [DBFT] |
4-10 |
$\mathbb{P}^1\times\mathrm{Bl}_2\mathbb{P}^2$ |
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4-11 |
blowup of 3-28 in $\{x\}\times E$, $x\in\mathbb{P}^1$ and $E$ the $(-1)$-curve |
$\mathbb{P}^1 \times \mathbb{P}^2 \times \mathbb{P}^1 \times \mathbb{P}^6$ |
$\mathcal{O}(0,1,1,0) \oplus \mathcal{Q}_{\mathbb{P}^2}(0,0,0,1) \oplus\Lambda(0,0,0,1) \oplus \mathcal{O}(0,0,-1,1)$
$\Lambda \in \operatorname{Ext}^1_{(\mathbb{P}^1)^2}(\mathcal{O}(0,1)^{\oplus 2}, \mathcal{O}(1, -1))$ |
[DBFT] |
4-12 |
blowup of 2-33 in the disjoint union of two exceptional lines of the blowup |
$ \mathbb{P}^1 \times \mathbb{P}^3 \times \mathbb{P}^{8}$ |
$\mathcal{O}(1,1,0) \oplus \Lambda(0,0,1) \oplus \mathcal{O}(-1,1,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1 \times \mathbb{P}^3}(\mathcal{Q}_{\mathbb{P}^3}^{\oplus 2},\mathcal{O}(1,-1))$ |
[DBFT] |
4-13 |
blowup of 3-27 in a curve of degree $(1,1,3)$ |
$ \mathbb{P}^1_1 \times \mathbb{P}^1_2 \times \mathbb{P}^1_3 \times \mathbb{P}^4$ |
$\Lambda(0,0,0,1) \oplus \mathcal{O}(1,0,1,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1_1 \times \mathbb{P}^1_2}(\mathcal{O}(0,1)^{\oplus 2}, \mathcal{O}(1, -1))$ |
[DBFT] |
5-1 |
blowup of 2-29 in the disjoint union of three exceptional lines of the blowup |
$\mathbb{P}^1 \times \mathbb{P}^3 \times \mathbb{P}^{8} \times \mathbb{P}^{11}$ |
$\mathcal{O}(1,1,0,0) \oplus \Lambda(0,0,1,0) \oplus \mathcal{O}(-1,1,1,0) \oplus \mathcal{Q}_{\mathbb{P}^3}(0,0,0,1) \oplus \mathcal{Q}_{\mathbb{P}^8}(0,0,0,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1 \times \mathbb{P}^3}(\mathcal{Q}_{\mathbb{P}^3}^{\oplus 2},\mathcal{O}(1,-1))$ |
[DBFT] |
5-2 |
blowup of 3-25 in the disjoint union of two exceptional lines on the same irreducible component |
$\mathbb{P}^1 \times \mathbb{P}^3 \times \mathbb{P}^{8} \times \mathbb{P}^1$ |
$\mathcal{O}(1,1,0,0) \oplus \Lambda(0,0,1,0) \oplus \mathcal{O}(-1,1,1,0) \oplus \mathcal{O}(0,1,0,1)$
$\Lambda \in \operatorname{Ext}^1_{\mathbb{P}^1 \times \mathbb{P}^3}(\mathcal{Q}_{\mathbb{P}^3}^{\oplus 2},\mathcal{O}(1,-1))$ |
[DBFT] |
5-3 |
$\mathbb{P}^1\times\mathrm{Bl}_3\mathbb{P}^2$ |
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6-1 |
$\mathbb{P}^1\times\mathrm{Bl}_4\mathbb{P}^2$ |
$\operatorname{Gr}(2,5) \times \mathbb{P}^1$ | $\mathcal{O}(1,0)^{\oplus 4}$ | classical |
7-1 |
$\mathbb{P}^1\times\mathrm{Bl}_5\mathbb{P}^2$ |
$\mathbb{P}^4 \times \mathbb{P}^1$ | $\mathcal{O}(2,0)^{\oplus 2}$ | classical |
8-1 |
$\mathbb{P}^1\times\mathrm{Bl}_6\mathbb{P}^2$ |
$\mathbb{P}^3 \times \mathbb{P}^1$ | $\mathcal{O}(3,0)$ | classical |
9-1 |
$\mathbb{P}^1\times\mathrm{Bl}_7\mathbb{P}^2$ |
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10-1 |
$\mathbb{P}^1\times\mathrm{Bl}_8\mathbb{P}^2$ |
$\mathbb{P}(1^2,2,3) \times \mathbb{P}^1$ | $\mathcal{O}(6,0)$ | classical |