1999/08/31 by Gunther Cornelissen, Cornelissen, Gunther · 1 citation
Mathematics · #11R29 #14H40 #Algebraic Geometry (math.AG) #FOS: Mathematics #Number Theory (math.NT) #math.AG #math.NT #msc:11R29 #msc:14H40
paper · pdf · doi:10.48550/arxiv.math/9908175
10 pages, LaTeX, uses `a4'
arxiv created 1999/09/01 · arxiv updated 2009/11/30
Let G be the separable Galois group of a finite field F of characteristic p, and X/F an imaginary hyperelliptic curve such that G acts transitively on its set W(X) of Weierstrass points. The existence of a G-invariant 2-torsion point on the Jacobian J(X) of X depends only on the parity of |W(X)|, but for large enough |F|, there exist two such curves X and X' with |W(X)|=|W(X')|, such that J(X) has (and J(X') does not have) a G-invariant 4-torsion point. The problem is equivalent to a study of the 2-,4- and 8-rank of the class number of the maximal order in the function field of such curves, and is investigated via the 2-primary class field tower. Contrary to the case of number fields, the ambiguous class depends on the discriminant, and a governing field for the 8-rank of such function fields is not known.