hyperelliptic(.ncag).info

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

$\mathrm{C}_{4} \times \mathrm{A}_4$ 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
$\mathrm{C}_{4} \times \mathrm{A}_4$, order $48$, SmallGroup $[48,31]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, 1, i)$
$\rho(g_{2}) = \operatorname{diag}(1, 1, \zeta_{3}, \zeta_{3}^{2})$
$\rho(g_{3}) = \operatorname{diag}(1, 1, 1, -1)$
$\rho(g_{4}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho(g_{5}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho \cong$ $\chi_{ 4 }$ $\oplus$ $\chi_{ 13 }$
order of $\omega_X$
4
number of moduli
1
irregularity $q = \dim \operatorname{Aut}^0(X)$
0
Albanese
the Albanese variety is a point; the fiber is $X$ itself (details)
$\mathbf{D}^{\mathrm{b}}(X)$
indecomposability open (why)
Hochschild cohomology $\dim \mathrm{HH}^\bullet$
$(1, 0, 1, 4, 1, 0, 1, 0, 0)$
Hodge diamond
1
0 0
0 2 0
1 1 1 1
0 0 2 0 0
1 1 1 1
0 2 0
0 0
1
polyvector fields $\mathrm{H}^q(X,\bigwedge^p T_X)$
1
00
010
1111
00100
0000
010
00
0

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

Since $\operatorname{ord} \omega_X = 4$, the twists by powers of the canonical bundle form a finite package of $4$ diamonds (explained).

$\omega_X^{\otimes 0}$
1
00
020
1111
00200
1111
020
00
1
$\omega_X^{\otimes 1}$
0
01
000
0010
01111
0010
000
01
0
$\omega_X^{\otimes 2}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 3}$
0
10
000
0100
11110
0100
000
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