Elliptic subfields and automorphisms of genus 2 function fields, by Tony Shaska and Helmut Voelklein

Elliptic subfields and automorphisms of genus 2 function fields, by Tony Shaska and Helmut Voelklein

We study genus 2 function fields with elliptic subfields of degree 2. The locus $\L_2$ of these fields is a 2-dimensional subvariety of the moduli space $\mathcal M_2$ of genus 2 fields. An equation for $\L_2$ is already in the work of Clebsch and Bolza. We use a birational parameterization of $\L_2$ by affine 2-space to study the relation between the j-invariants of the degree 2 elliptic subfields. This extends work of Geyer, Gaudry, Stichtenoth and others. We find a 1-dimensional family of genus 2 curves having exactly two isomorphic elliptic subfields of degree 2; this family is parameterized by the j-invariant of these subfields.

d2.dvi (142596 bytes) [2001 Jul 20]
d2.dvi.gz (55231 bytes)
d2.ps (311381 bytes)
d2.ps.gz (101418 bytes)

Tony Shaska and Helmut Voelklein <tshaska@math.uci.edu>