Mapping classes of Real Rational Surface Automorphisms

Abstract

Let $\{F_n,n\ge 8\}$ be a family of diffeomorphisms on real rational surfaces that are birationally equivalent to birational maps on ${\mathbf{P}}^2(\mathbb{R})$. In this article, we investigate the mapping classes of the diffeomorphisms $F_n,n\ge 8$. These diffeomorphisms are reducible with unique invariant irreducible curves, and we determine the mapping classes of their restrictions, ${\hat{F}}_n,n\ge 8$, on the cut surfaces, showing that they are pseudo-Anosov and do not arise from Penner's construction. For $n=8$, Lehmer's number is realized as the stretch factor of ${\hat{F}}_8$, a pseudo-Anosov map on a once-punctured genus $5$ orientable surface. The diffeomorphism ${\hat{F}}_8$ is a new geometric realization of a Lehmer's number.