Paper detail

Permutation modules and Chow motives of geometrically rational surfaces

We prove that the Chow motive with integral coefficient of a geometrically rational surfaces~$S$ over a perfect field~$k$ is zero dimensional if and only if the Picard group of~$\bar{k}\times_{k}S$, where~$\bar{k}$ is an algebraic closure of~$k$, is a direct summand of a $\Gal (\bar{k}/k)$-permutation module, and~$S$ possesses a zero cycle of degree one. As shown by Colliot-Thélène in a letter to the author (which we have reproduced in the appendix) this is in turn equivalent to~$S$ having a zero cycle of degree~$1$ and $\CH_{0}(k(S)\times_{k}S)$ being torsion free.