Non-orientable automorphisms of Riemann surfaces

Abstract

We study cyclic groups of automorphisms of Riemann surfaces that contain non-orientable elements. We obtain conditions for such a group, and calculate the minimum possible genus of the surface on which it acts. As a consequence of these results we obtain that the order of a sense- reversing automorphism of a Riemann surface of genus g is at most $4g+4$ for even g and 4g-4 for odd g, and that both bounds are attained for every g.