hyperelliptic(.ncag).info

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

$\mathrm{C}_{3} \times \mathrm{D}_4$ 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
$\mathrm{C}_{3} \times \mathrm{D}_4$, order $24$, SmallGroup $[24,10]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, 1, -1)$
$\rho(g_{2}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho(g_{3}) = \operatorname{diag}(1, \zeta_{3}, \zeta_{3}, \zeta_{3}^{2})$
$\rho(g_{4}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho \cong$ $\chi_{ 1 }$ $\oplus$ $\chi_{ 6 }$ $\oplus$ $\chi_{ 14 }$
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 $\dim \mathrm{HH}^\bullet$
$(1, 2, 1, 0, 1, 2, 1, 0, 0)$
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
00100
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
030
0220
00400
0220
030
11
1
$\omega_X^{\otimes 1}$
0
00
000
0101
01111
0101
000
00
0
$\omega_X^{\otimes 2}$
0
00
000
0010
00110
0010
000
00
0
$\omega_X^{\otimes 3}$
0
00
010
0220
01410
0220
010
00
0
$\omega_X^{\otimes 4}$
0
00
000
0100
01100
0100
000
00
0
$\omega_X^{\otimes 5}$
0
00
000
1010
11110
1010
000
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