hyperelliptic(.ncag).info

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

$\mathrm{S}_3 \times \mathrm{C}_2$ 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
$\mathrm{S}_3 \times \mathrm{C}_2$, order $12$, SmallGroup $[12,4]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, 1, -1)$
$\rho(g_{2}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho(g_{3}) = \operatorname{diag}(1, 1, \zeta_{3}, \zeta_{3}^{2})$
$\rho \cong$ $2\,\chi_{ 1 }$ $\oplus$ $\chi_{ 6 }$
order of $\omega_X$
2
number of moduli
5
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 $\dim \mathrm{HH}^\bullet$
$(1, 4, 7, 8, 8, 8, 7, 4, 1)$
Hodge diamond
1
2 2
1 5 1
0 4 4 0
0 1 6 1 0
0 4 4 0
1 5 1
2 2
1
polyvector fields $\mathrm{H}^q(X,\bigwedge^p T_X)$
1
22
151
0440
01610
0440
151
22
1

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

Since $\operatorname{ord} \omega_X = 2$, the twists by powers of the canonical bundle form a finite package of $2$ diamonds (explained).

$\omega_X^{\otimes 0}$
1
22
151
0440
01610
0440
151
22
1
$\omega_X^{\otimes 1}$
0
00
111
2442
15651
2442
111
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