Rationality of conic bundle threefolds over non-closed fields

Abstract: Clemens–Griffiths introduced the classical intermediate Jacobian obstruction to rationality for complex threefolds, and used it to show irrationality of the cubic threefold. Recently, over non-closed fields, Hassett–Tschinkel and Benoist–Wittenberg refined this obstruction using torsors over the intermediate Jacobian. In this talk, we identify these intermediate Jacobian torsors for conic bundle threefolds, and we give applications to rationality over non-closed fields. This talk is based on joint work with S. Frei, S. Sankar, B. Viray, and I. Vogt, and on joint work with M. Ji.

algebraic geometrynumber theory

Audience: researchers in the topic

SFU NT-AG seminar

Series comments: The Number Theory and Algebraic Geometry (NT-AG) seminar is a research seminar dedicated to topics related to number theory and algebraic geometry hosted by the NT-AG group (Nils Bruin, Imin Chen, Stephen Choi, Katrina Honigs, Nathan Ilten, Marni Mishna).

We acknowledge the support of PIMS, NSERC, and SFU.

For Fall 2025, the organizers are Katrina Honigs and Peter McDonald.

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