hyperelliptic(.ncag).info

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

$\mathrm{C}_{3} \times \mathrm{Q}_8$ 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
$\mathrm{C}_{3} \times \mathrm{Q}_8$, order $24$, SmallGroup $[24,11]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, i, -i)$
$\rho(g_{2}) = \operatorname{diag}(1, i, -1, -i)$
$\rho(g_{3}) = \operatorname{diag}(1, \zeta_{3}, \zeta_{3}, \zeta_{3}^{2})$
$\rho(g_{4}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho \cong$ $\chi_{ 1 }$ $\oplus$ $\chi_{ 6 }$ $\oplus$ $\chi_{ 14 }$
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 $\dim \mathrm{HH}^\bullet$
$(1, 2, 1, 0, 3, 6, 3, 0, 0)$
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
01110
1221
111
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
11
030
0220
00400
0220
030
11
1
$\omega_X^{\otimes 1}$
0
10
110
0201
01111
0201
110
10
0
$\omega_X^{\otimes 2}$
0
00
001
0021
00130
0021
001
00
0
$\omega_X^{\otimes 3}$
0
00
010
0220
01410
0220
010
00
0
$\omega_X^{\otimes 4}$
0
00
100
1200
03100
1200
100
00
0
$\omega_X^{\otimes 5}$
0
01
011
1020
11110
1020
011
01
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