English

The pseudo-fundamental group-scheme

Algebraic Geometry 2019-05-06 v2

Abstract

Let XX be any scheme defined over a Dedekind scheme SS with a given section xX(S)x\in X(S). We prove the existence of a pro-finite SS-group scheme (X,x)\aleph(X,x) and a universal (X,x)\aleph(X,x)-torsor dominating all the pro-finite pointed torsors over XX. Though (X,x)\aleph(X,x) may not be unique in general it still can provide useful information in order to better understand XX. In a similar way we prove the existence of a pro-algebraic SS-group scheme alg(X,x)\aleph^{\rm alg}(X,x) and a alg(X,x)\aleph^{\rm alg}(X,x)-torsor dominating all the pro-algebraic and affine pointed torsors over XX. The case where XSX\to S has no sections is also considered.

Keywords

Cite

@article{arxiv.1602.04644,
  title  = {The pseudo-fundamental group-scheme},
  author = {Marco Antei and Arijit Dey},
  journal= {arXiv preprint arXiv:1602.04644},
  year   = {2019}
}

Comments

Final accepted version

R2 v1 2026-06-22T12:50:19.358Z