hyperelliptic(.ncag).info

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

$\mathrm{C}_{6} \times \mathrm{C}_{6}$ 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
$\mathrm{C}_{6} \times \mathrm{C}_{6}$, order $36$, SmallGroup $[36,14]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, -1, 1)$
$\rho(g_{2}) = \operatorname{diag}(1, 1, 1, -1)$
$\rho(g_{3}) = \operatorname{diag}(1, \zeta_{3}, \zeta_{3}, 1)$
$\rho(g_{4}) = \operatorname{diag}(1, 1, 1, \zeta_{3})$
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 $\dim \mathrm{HH}^\bullet$
$(1, 2, 1, 2, 4, 2, 0, 0, 0)$
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
010
0110
01210
0110
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
010
0111
00211
0111
010
00
0
$\omega_X^{\otimes 2}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 3}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 4}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 5}$
0
00
010
1110
11200
1110
010
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