Zeta functions of a class of Artin-Schreier curves with many   automorphisms
  This paper describes a class of Artin-Schreier curves, generalizing results of Van der Geer and Van der Vlugt to odd characteristic. The automorphism group of these curves contains a large extraspecial group as a subgroup. Precise knowledge of this subgroup makes it possible to compute the zeta functions of the curves in the class over the field of definition of all automorphisms in the subgroup. As a consequence, we obtain new examples of maximal curves. 
Irene Bouw, Wei Ho, Beth Malmskog, Renate Scheidler, Padmavathi   Srinivasan, and Christelle Vincent
math.AG math.NT