On symplectic automorphisms of elliptic surfaces acting on $\mathrm{CH}_0$

Abstract

Let $S$ be a complex smooth projective surface of Kodaira dimension one. We show that the group $\mathrm{Aut}_s(S)$ of symplectic automorphisms acts trivially on the Albanese kernel $\mathrm{CH}_0(S)_\mathrm{alb}$ of the $0$-th Chow group $\mathrm{CH}_0(S)$, unless possibly if the geometric genus and the irregularity satisfy $p_g(S)=q(S)\in\{1,2\}$. In the exceptional cases, the image of the homomorphism $\mathrm{Aut}_s(S)\rightarrow \mathrm{Aut}(\mathrm{CH}_0(S)_\mathrm{alb})$ has order at most 3. Our arguments actually take care of the group $\mathrm{Aut}_f(S)$ of fibration-preserving automorphisms of elliptic surfaces $f\colon S\rightarrow B$. We prove that, if $\sigma\in\mathrm{Aut}_f(S)$ induces the trivial action on $H^{i,0}(S)$ for $i>0$, then it induces the trivial action on $\mathrm{CH}_0(S)_\mathrm{alb}$. As a by-product we obtain that if $S$ is an elliptic K3 surface, then $\mathrm{Aut}_f(S)\cap \mathrm{Aut}_s(S)$ acts trivially on $\mathrm{CH}_0(S)_\mathrm{alb}$.