Algebraic models of the line in the real affine plane

Adrien Dubouloz (1) , Frédéric Mangolte (2)

1 IMB - Institut de Mathématiques de Bourgogne [Dijon]
2 LAREMA - Laboratoire Angevin de Recherche en Mathématiques

We study smooth rational closed embeddings of the real affine line into the real affine plane, that is algebraic rational maps from the real affine line to the real affine plane which induce smooth closed embeddings of the real euclidean line into the real euclidean plane. We consider these up to equivalence under the group of birational automorphisms of the real affine plane which are diffeomorphisms of its real locus. We show that in contrat with the situation in the categories of smooth manifolds with smooth maps and of real algebraic varieties with regular maps where there is only one equivalence class up to isomorphism, there are plenty of non-equivalent smooth rational closed embeddings up to such birational diffeomorphisms. Some of these are simply detected by the non-negativity of the real Kodaira dimension of the complement of their images. But we also introduce finer invariants derived from topological properties of suitable fake real planes associated to certain classes of such embeddings.

Domaines: Géométrie algébrique [math.AG]

Adrien Dubouloz, Frédéric Mangolte. Algebraic models of the line in the real affine plane. 2018. ⟨hal-01802038v1⟩