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 $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, i, -i)$
$\rho(g_{2}) = \operatorname{diag}(1, i, -1, -i)$
$\rho(g_{3}) = \operatorname{diag}(1, 1, 1, \zeta_{3}^{2})$
$\rho(g_{4}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho \cong$ $\chi_{ 1 }$ $\oplus$ $\chi_{ 6 }$ $\oplus$ $\chi_{ 13 }$
order of $\omega_X$
6
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 $\dim \mathrm{HH}^\bullet$
$(1, 2, 4, 6, 4, 2, 1, 0, 0)$
Hodge diamond
1
1 1
1 3 1
1 3 3 1
0 2 4 2 0
1 3 3 1
1 3 1
1 1
1
polyvector fields $\mathrm{H}^q(X,\bigwedge^p T_X)$
1
11
121
1221
01210
0110
010
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
131
1331
02420
1331
131
11
1
$\omega_X^{\otimes 1}$
0
01
011
0121
01221
0121
011
01
0
$\omega_X^{\otimes 2}$
0
00
000
0100
01100
0100
000
00
0
$\omega_X^{\otimes 3}$
0
00
010
0110
00200
0110
010
00
0
$\omega_X^{\otimes 4}$
0
00
000
0010
00110
0010
000
00
0
$\omega_X^{\otimes 5}$
0
10
110
1210
12210
1210
110
10
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