The order of finite algebraic fundamental groups of surfaces with K^2<=3χ-2

Abstract

We study the structure of the algebraic fundamental group for minimal surfaces of general type S satisfying K_S^2<=3χ-2$ and not having any irregular etale cover. We show that, if K_S^2<=3χ-2, then then the algebraic fundamental group of S has order at most 5, and equality only occurs if S is a Godeaux surface. We also show that if K_S^2<= 3χ-3 and the algebraic fundamental group of S is not trivial, then it is Z_2, or Z_2^2 or Z_3. Furthermore in this last case one has: 2<=χ<=4, K^2=3χ-3 and these possibilities do occur.