hyperelliptic(.ncag).info

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

$\mathrm{C}_{6} \times \mathrm{C}_{3}$ 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
$\mathrm{C}_{6} \times \mathrm{C}_{3}$, order $18$, SmallGroup $[18,5]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, -1, 1, 1)$
$\rho(g_{2}) = \operatorname{diag}(1, 1, \zeta_{3}, 1)$
$\rho(g_{3}) = \operatorname{diag}(1, 1, 1, \zeta_{3})$
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 $\dim \mathrm{HH}^\bullet$
$(1, 2, 2, 2, 1, 0, 0, 0, 0)$
Hodge diamond
1
1 1
0 4 0
0 3 3 0
0 0 6 0 0
0 3 3 0
0 4 0
1 1
1
polyvector fields $\mathrm{H}^q(X,\bigwedge^p T_X)$
1
11
020
0110
00100
0000
000
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
040
0330
00600
0330
040
11
1
$\omega_X^{\otimes 1}$
0
00
000
0011
00121
0011
000
00
0
$\omega_X^{\otimes 2}$
0
00
100
1100
02000
1100
100
00
0
$\omega_X^{\otimes 3}$
0
11
121
0330
02420
0330
121
11
0
$\omega_X^{\otimes 4}$
0
00
001
0011
00020
0011
001
00
0
$\omega_X^{\otimes 5}$
0
00
000
1100
12100
1100
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