arXiv subjects

Viktor Balch Barth

Publications and source records attributed to Viktor Balch Barth.

3 recordsLinked to original sources

arXiv2024

Making the motivic group structure on the endomorphisms of the projective line explicit

We construct a group structure on the set of pointed naive homotopy classes of scheme morphisms from the Jouanolou device to the projective line. The group operation is defined via matrix multiplication on generating sections of line bundles and only requires basic algebraic geometry. In particular, it is completely independent of the construction of the motivic homotopy category. We show that a particular scheme morphism, which exhibits the Jouanolou device as an affine torsor bundle over the projective line, induces a monoid morphism from Cazanave's monoid to this group. Moreover, we show that this monoid morphism is a group completion to a subgroup of the group of scheme morphisms from the Jouanolou device to the projective line. This subgroup is generated by a set of morphisms that are simple to describe.

math.AG↗

arXiv2023

Images of dominant endomorphisms of affine space

A basic problem in the study of algebraic morphisms is to determine which sets can be realised as the image of an endomorphism of affine space. This paper extends the results previously obtained by the first author on the question of existence of surjective maps $F\colon \mathbb{A}^n \rightarrow \mathbb{A}^n\setminus Z$, where $Z$ is an algebraic subvariety of $\mathbb{A}^n$ of codimension at least 2. In particular, we show that for any (affine) algebraic variety $Z$ of dimension at most $n-2$, there is an algebraic variety $W\subset \mathbb{A}^n$ birational to $Z$ and a surjective algebraic morphism $\mathbb{A}^n\rightarrow \mathbb{A}^n\setminus W$. We also propose a conjectural approach towards resolving unknown cases.

math.AG↗

arXiv2023

Surjective morphisms from affine space to its Zariski open subsets

We prove constructively the existence of surjective morphisms from affine space onto certain open subvarieties of affine space of the same dimension. For any algebraic set $Z\subset \mathbb{A}^{n-2}\subset \mathbb{A}^{n}$, we construct an endomorphism of $\mathbb{A}^{n}$ with $\mathbb{A}^{n} \setminus Z$ as its image. By Noether's normalization lemma, these results extend to give surjective maps from any $n$-dimensional affine variety $X$ to $\mathbb{A}^{n} \setminus Z$.

math.AG↗