hyperelliptic(.ncag).info

the classification of hyperelliptic varieties in dimensions 2, 3 and 4

$((\mathrm{C}_2 \times \mathrm{C}_6) \rtimes \mathrm{C}_2) \times \mathrm{C}_3$ 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
$((\mathrm{C}_2 \times \mathrm{C}_6) \rtimes \mathrm{C}_2) \times \mathrm{C}_3$, order $72$, SmallGroup $[72,30]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, 1, -1)$
$\rho(g_{2}) = \operatorname{diag}(1, 1, 1, -1)$
$\rho(g_{3}) = \operatorname{diag}(1, \zeta_{3}, \zeta_{3}, \zeta_{3}^{2})$
$\rho(g_{4}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho(g_{5}) = \operatorname{diag}(1, 1, \zeta_{3}, \zeta_{3}^{2})$
$\rho \cong$ $\chi_{ 1 }$ $\oplus$ $\chi_{ 5 }$ $\oplus$ $\chi_{ 24 }$
order of $\omega_X$
6
number of moduli
1
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 $\dim \mathrm{HH}^\bullet$
$(1, 2, 1, 0, 0, 2, 4, 2, 0)$
Hodge diamond
1
1 1
0 3 0
0 2 2 0
0 0 4 0 0
0 2 2 0
0 3 0
1 1
1
polyvector fields $\mathrm{H}^q(X,\bigwedge^p T_X)$
1
11
010
0000
00000
0110
121
11
0

twisted Hodge numbers $\mathrm{h}^{p,q}(X,\omega_X^{\otimes j})$

Since $\operatorname{ord} \omega_X = 6$, the twists by powers of the canonical bundle form a finite package of $6$ diamonds (explained).

$\omega_X^{\otimes 0}$
1
11
030
0220
00400
0220
030
11
1
$\omega_X^{\otimes 1}$
0
00
100
1101
02011
1101
100
00
0
$\omega_X^{\otimes 2}$
0
01
011
0020
00110
0020
011
01
0
$\omega_X^{\otimes 3}$
0
00
000
0110
01210
0110
000
00
0
$\omega_X^{\otimes 4}$
0
10
110
0200
01100
0200
110
10
0
$\omega_X^{\otimes 5}$
0
00
001
1011
11020
1011
001
00
0

References

  1. A. Demleitner, The classification of hyperelliptic groups in dimension 4. arXiv:2211.07998
  2. A. Demleitner, C. Gleissner, The classification of rigid hyperelliptic fourfolds, Ann. Mat. Pura Appl. (4) 202 (2023) 1425–1450. MR4576947 doi
  3. P. Belmans, A. Demleitner, P. Núñez, The Albanese morphism for hyperelliptic varieties, Indag. Math. (N.S.) 37 (2026) 1450–1475. MR5103244 doi