$\mathrm{C}_{12} \times \mathrm{C}_{2}$ in dimension 4
This tangent representation satisfies the necessary conditions for a hyperelliptic fourfold, but it is not known whether it is realized by an actual variety. See completeness in dimension 4.
- holonomy group
- $\mathrm{C}_{12} \times \mathrm{C}_{2}$, order $24$, SmallGroup $[24,9]$ · character table
- tangent representation $\rho$
- $\rho(g_{1}) = \operatorname{diag}(1, -1, 1, 1)$$\rho(g_{2}) = \operatorname{diag}(1, \zeta_{3}, 1, 1)$$\rho(g_{3}) = \operatorname{diag}(1, 1, i, -1)$
- order of $\omega_X$
- 12
- number of moduli
- 2
- irregularity $q = \dim \operatorname{Aut}^0(X)$
- 1
- Albanese
- the Albanese variety has dimension $1$; the general fiber has dimension $3$ and is an abelian variety or a hyperelliptic variety (details)
- $\mathbf{D}^{\mathrm{b}}(X)$
- indecomposability open (why)
- Hochschild cohomology $\dim \mathrm{HH}^\bullet$
- $(1, 2, 2, 4, 5, 2, 0, 0, 0)$
Hodge diamond
1
1 1
0 4 0
0 3 3 0
0 0 6 0 0
0 3 3 0
0 4 0
1 1
1
1 1
0 4 0
0 3 3 0
0 0 6 0 0
0 3 3 0
0 4 0
1 1
1
polyvector fields $\mathrm{H}^q(X,\bigwedge^p T_X)$
1
11
020
0220
01310
0110
000
00
0
11
020
0220
01310
0110
000
00
0
twisted Hodge numbers $\mathrm{h}^{p,q}(X,\omega_X^{\otimes j})$
Since $\operatorname{ord} \omega_X = 12$, the twists by powers of the canonical bundle form a finite package of $12$ diamonds (explained).
$\omega_X^{\otimes 0}$
1
11
040
0330
00600
0330
040
11
1
11
040
0330
00600
0330
040
11
1
$\omega_X^{\otimes 1}$
0
00
010
0121
00321
0121
010
00
0
00
010
0121
00321
0121
010
00
0
$\omega_X^{\otimes 2}$
0
00
000
0000
00000
0000
000
00
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 3}$
0
00
000
0000
00000
0000
000
00
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 4}$
0
00
000
0000
00000
0000
000
00
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 5}$
0
00
100
1210
03210
1210
100
00
0
00
100
1210
03210
1210
100
00
0
$\omega_X^{\otimes 6}$
0
11
121
0330
02420
0330
121
11
0
11
121
0330
02420
0330
121
11
0
$\omega_X^{\otimes 7}$
0
00
001
0121
01230
0121
001
00
0
00
001
0121
01230
0121
001
00
0
$\omega_X^{\otimes 8}$
0
00
000
0000
00000
0000
000
00
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 9}$
0
00
000
0000
00000
0000
000
00
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 10}$
0
00
000
0000
00000
0000
000
00
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 11}$
0
00
010
1210
12300
1210
010
00
0
00
010
1210
12300
1210
010
00
0
References
- A. Demleitner, The classification of hyperelliptic groups in dimension 4. arXiv:2211.07998
- A. Demleitner, C. Gleissner, The classification of rigid hyperelliptic fourfolds, Ann. Mat. Pura Appl. (4) 202 (2023) 1425–1450. MR4576947 doi
- P. Belmans, A. Demleitner, P. Núñez, The Albanese morphism for hyperelliptic varieties, Indag. Math. (N.S.) 37 (2026) 1450–1475. MR5103244 doi