April 13, 2026

Quasifibrations in étale homotopy theory

Tim Holzschuh, IHES, FR RIMS Kyoto (Building 15 - Room 201) [map & Information] + Zoom · JP: 15:30 · FR: 08:30

Let S be a noetherian and normal scheme and \(f\colon X \to S\) a geometric fibration (e.g. a smooth and proper morphism) with geometrically connected fibres.

In [Fri73], Friedlander proved that, after completion away from char(S), the étale homotopy type of a geometric fibre of f coincides with the homotopy fibre of the induced map on étale homotopy types.

In this talk, I will explain a more conceptual proof (strategy) of Friedlanders result that works for arbitrary qcqs schemes S. This is joint work in progress with Alexander Schmidt and Jakob Stix.

  1. A. Dold, R. Thom. Quasifaserungen und unendliche symmetrische Produkte, Annals of Mathematics, 1958
  2. E. M. Friedlander. The etale homotopy theory of a geometric fibration, Manuscripta Mathematica, 1973
  3. P. J. Haine, T. Holzschuh, S. Wolf. Nonabelian basechange theorems and étale homotopy theory, Journal of Topology, 2024

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