$\mathrm{C}_{4} \times \mathrm{A}_4$ 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
- $\mathrm{C}_{4} \times \mathrm{A}_4$, order $48$, SmallGroup $[48,31]$ · character table
- tangent representation $\rho$
- $\rho(g_{1}) = \operatorname{diag}(1, 1, 1, i)$$\rho(g_{2}) = \operatorname{diag}(1, 1, \zeta_{3}, \zeta_{3}^{2})$$\rho(g_{3}) = \operatorname{diag}(1, 1, 1, -1)$$\rho(g_{4}) = \operatorname{diag}(1, 1, -1, -1)$$\rho(g_{5}) = \operatorname{diag}(1, 1, -1, -1)$$\rho \cong$ $\chi_{ 4 }$ $\oplus$ $\chi_{ 13 }$
- order of $\omega_X$
- 4
- number of moduli
- 1
- irregularity $q = \dim \operatorname{Aut}^0(X)$
- 0
- Albanese
- the Albanese variety is a point; the fiber is $X$ itself (details)
- $\mathbf{D}^{\mathrm{b}}(X)$
- indecomposability open (why)
- Hochschild cohomology $\dim \mathrm{HH}^\bullet$
- $(1, 0, 1, 4, 1, 0, 1, 0, 0)$
Hodge diamond
1
0 0
0 2 0
1 1 1 1
0 0 2 0 0
1 1 1 1
0 2 0
0 0
1
0 0
0 2 0
1 1 1 1
0 0 2 0 0
1 1 1 1
0 2 0
0 0
1
polyvector fields $\mathrm{H}^q(X,\bigwedge^p T_X)$
1
00
010
1111
00100
0000
010
00
0
00
010
1111
00100
0000
010
00
0
twisted Hodge numbers $\mathrm{h}^{p,q}(X,\omega_X^{\otimes j})$
Since $\operatorname{ord} \omega_X = 4$, the twists by powers of the canonical bundle form a finite package of $4$ diamonds (explained).
$\omega_X^{\otimes 0}$
1
00
020
1111
00200
1111
020
00
1
00
020
1111
00200
1111
020
00
1
$\omega_X^{\otimes 1}$
0
01
000
0010
01111
0010
000
01
0
01
000
0010
01111
0010
000
01
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
10
000
0100
11110
0100
000
10
0
10
000
0100
11110
0100
000
10
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