English

Odd fake $\mathbb{Q}$ -homology quadrics exist

Algebraic Geometry 2025-08-26 v2 Algebraic Topology

Abstract

We show the existence of odd fake Q\mathbb{Q}-homology quadrics, namely of minimal surfaces SS of general type which have the same Q\mathbb{Q}-homology as a smooth quadric Q(P1(C))2Q \cong (\mathbb{P}^1(\mathbb{C}))^2, but have an odd intersection form on H2(S,Z)/Tors(S) H^2(S, \mathbb{Z})/Tors(S), where Tors(S)Tors(S) is the Torsion subgroup. Our examples are provided by a special 1-dimensional family of surfaces isogenous to a product of unmixed type.

Keywords

Cite

@article{arxiv.2504.17475,
  title  = {Odd fake $\mathbb{Q}$ -homology quadrics exist},
  author = {Fabrizio Catanese},
  journal= {arXiv preprint arXiv:2504.17475},
  year   = {2025}
}

Comments

9 pages, added a few lines of explanation, answering a question by Young-Seog Lee

R2 v1 2026-06-28T23:09:47.055Z