hyperelliptic(.ncag).info

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

$\mathrm{C}_{12} \times \mathrm{C}_{2}$ 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
$\mathrm{C}_{12} \times \mathrm{C}_{2}$, order $24$, SmallGroup $[24,9]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, -1, 1, -1)$
$\rho(g_{2}) = \operatorname{diag}(1, \zeta_{3}, 1, \zeta_{3})$
$\rho(g_{3}) = \operatorname{diag}(1, 1, i, -1)$
order of $\omega_X$
12
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 $\dim \mathrm{HH}^\bullet$
$(1, 2, 1, 0, 0, 0, 0, 0, 0)$
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
010
0000
00000
0000
000
00
0

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

Since $\operatorname{ord} \omega_X = 12$, the twists by powers of the canonical bundle form a finite package of $12$ diamonds (explained).

$\omega_X^{\otimes 0}$
1
11
040
0330
00600
0330
040
11
1
$\omega_X^{\otimes 1}$
0
00
000
0001
00011
0001
000
00
0
$\omega_X^{\otimes 2}$
0
00
100
1100
02000
1100
100
00
0
$\omega_X^{\otimes 3}$
0
01
011
0230
02420
0230
011
01
0
$\omega_X^{\otimes 4}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 5}$
0
00
000
0100
01100
0100
000
00
0
$\omega_X^{\otimes 6}$
0
00
020
0220
00400
0220
020
00
0
$\omega_X^{\otimes 7}$
0
00
000
0010
00110
0010
000
00
0
$\omega_X^{\otimes 8}$
0
00
000
0000
00000
0000
000
00
0
$\omega_X^{\otimes 9}$
0
10
110
0320
02420
0320
110
10
0
$\omega_X^{\otimes 10}$
0
00
001
0011
00020
0011
001
00
0
$\omega_X^{\otimes 11}$
0
00
000
1000
11000
1000
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