Automorphisms of surfaces of general type with q=1 acting trivially in cohomology

Abstract

Let S be a complex minimal surface of general type with irregularity q(S)=1 and Aut_0(S) the subgroup of automorphisms acting trivially on the cohomology ring with rational coefficients. In this paper we show that |Aut_0(S)|<=4, and if the equality holds then $S$ is a surface isogenous to a product of unmixed type. Moreover, examples of surfaces with |Aut_0(S)|=4 and all possible values of the geometric genus are provided.