hyperelliptic(.ncag).info

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

$\mathrm{C}_{2} \times \mathrm{A}_4$ 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
$\mathrm{C}_{2} \times \mathrm{A}_4$, order $24$, SmallGroup $[24,13]$ · character table
tangent representation $\rho$
$\rho(g_{1}) = \operatorname{diag}(1, 1, 1, -1)$
$\rho(g_{2}) = \operatorname{diag}(1, \zeta_{3}, \zeta_{3}^{2}, \zeta_{3}^{2})$
$\rho(g_{3}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho(g_{4}) = \operatorname{diag}(1, 1, -1, -1)$
$\rho \cong$ $\chi_{ 4 }$ $\oplus$ $\chi_{ 7 }$
order of $\omega_X$
6
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 $\dim \mathrm{HH}^\bullet$
$(1, 0, 1, 4, 2, 2, 2, 0, 0)$
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
00200
0110
020
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
00
020
1111
00200
1111
020
00
1
$\omega_X^{\otimes 1}$
0
01
000
0110
02211
0110
000
01
0
$\omega_X^{\otimes 2}$
0
00
010
0110
00200
0110
010
00
0
$\omega_X^{\otimes 3}$
0
00
000
0110
01210
0110
000
00
0
$\omega_X^{\otimes 4}$
0
00
010
0110
00200
0110
010
00
0
$\omega_X^{\otimes 5}$
0
10
000
0110
11220
0110
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