The real Mordell-Weil group of rational elliptic surfaces and real lines on del Pezzo surfaces of degree $K^2=1$

Abstract

We undertake a study of topological properties of the real Mordell-Weil group $\operatorname{MW}_{\mathbb R}$ of real rational elliptic surfaces $X$ which we accompany by a related study of real lines on $X$ and on the "subordinate" del Pezzo surfaces $Y$ of degree 1. We give an explicit description of isotopy types of real lines on $Y_{\mathbb R}$ and an explicit presentation of $\operatorname{MW}_{\mathbb R}$ in the mapping class group $\operatorname{Mod}(X_{\mathbb R})$. Combining these results we establish an explicit formula for the action of $\operatorname{MW}_{\mathbb R}$ in $H_1(X_{\mathbb R})$.