hyperelliptic(.ncag).info

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

$\mathrm{C}_{6} \times \mathrm{C}_{6}$ 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
$\mathrm{C}_{6} \times \mathrm{C}_{6}$, order $36$, SmallGroup $[36,14]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, -1, 1)$
$\rho(g_{2}) = \operatorname{diag}(1, 1, 1, -1)$
$\rho(g_{3}) = \operatorname{diag}(1, 1, \zeta_{3}, 1)$
$\rho(g_{4}) = \operatorname{diag}(1, 1, 1, \zeta_{3})$
order of $\omega_X$
6
number of moduli
4
irregularity $q = \dim \operatorname{Aut}^0(X)$
2
Albanese
the Albanese variety has dimension $2$; the general fiber has dimension $2$ and is an abelian variety or a hyperelliptic variety (details)
$\mathbf{D}^{\mathrm{b}}(X)$
indecomposable
Hochschild cohomology $\dim \mathrm{HH}^\bullet$
$(1, 4, 6, 4, 1, 0, 0, 0, 0)$
Hodge diamond
1
2 2
1 6 1
0 6 6 0
0 2 10 2 0
0 6 6 0
1 6 1
2 2
1
polyvector fields $\mathrm{H}^q(X,\bigwedge^p T_X)$
1
22
141
0220
00100
0000
000
00
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
22
161
0660
021020
0660
161
22
1
$\omega_X^{\otimes 1}$
0
00
001
0022
00141
0022
001
00
0
$\omega_X^{\otimes 2}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 3}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 4}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 5}$
0
00
100
2200
14100
2200
100
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