In mathematics, a hyperelliptic surface, or bi-elliptic surface, is a surface with an elliptic fibration over an elliptic curve. Any such surface can be written as the quotient of a product of two elliptic curves by a finite abelian group. Hyperelliptic surfaces form one of the classes of surfaces of Kodaira dimension 0 in the Enriques–Kodaira classification.
The Kodaira dimension is 0.
Any hyperelliptic surface is a quotient (E×F)/G, where E = C/Λ and F are elliptic curves, and G is a subgroup of F (acting on F by translations). There are seven families of hyperelliptic surfaces as in the following table.
|order of K||Λ||G||Action of G on E|
|2||Any||Z/2Z||e → −e|
|2||Any||Z/2Z ⊕ Z/2Z||e → −e, e → e+c, −c=c|
|3||Z ⊕ Zω||Z/3Z||e → ωe|
|3||Z ⊕ Zω||Z/3Z ⊕ Z/3Z||e → ωe, e → e+c, ωc=c|
|4||Z ⊕ Zi;||Z/4Z||e → ie|
|4||Z ⊕ Zi||Z/4Z ⊕ Z/2Z||e → ie, e → e+c, ic=c|
|6||Z ⊕ Zω||Z/6Z||e → −ωe|
Here ω is a primitive cube root of 1 and i is a primitive 4th root of 1.
Quasi hyperelliptic surfaces
A quasi-hyperelliptic surface is a surface whose canonical divisor is numerically equivalent to zero, the Albanese mapping maps to an elliptic curve, and all its fibers are rational with a cusp. They only exist in characteristics 2 or 3. Their second Betti number is 2, the second Chern number vanishes, and the holomorphic Euler characteristic vanishes. They were classified by (Bombieri & Mumford 1976), who found six cases in characteristic 3 (in which case 6K= 0) and eight in characteristic 2 (in which case 6K or 4K vanishes). Any quasi-hyperelliptic surface is a quotient (E×F)/G, where E is a rational curve with one cusp, F is an elliptic curve, and G is a finite subgroup scheme of F (acting on F by translations).
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- Bombieri, Enrico; Mumford, David (1977), "Enriques' classification of surfaces in char. p. II", Complex analysis and algebraic geometry, Tokyo: Iwanami Shoten, pp. 23–42, MR 0491719