Severi type inequalities for irregular surfaces with ample canonical class

Abstract

Let S be a smooth minimal complex projective surface of maximal Albanese dimension. Under the assumption that the canonical class of S is ample and the irregularity of S, q(S), is greater or equal to 5 we show that K^2>= 4\chi(S)+(10/3)q(S)-8, thus improving the well known Severi inequality K^2>=4\chi(S). We also give stronger inequalities under extra assumptions on the Albanese map or on the canonical map of S.