Time：14:00-15:00, Friday, October 9 2026
Venue：E14-301
Speaker：Yang CAO, Shandong University
Title：New step in strong approximation for linear algebraic groups
Abstract：The classical theory of strong approximation for linear algebraic groups, developed by Kneser, Prasad, and Platonov in the 1960s, only consider the semi-simple simply connected case; the series works by Colliot-Thelene, Xu, Harari, and Demarche extended these results to more general groups, which necessarily needed cohomological obstructions. In this talk, I will present new approaches to strong approximation that avoid to use the abstract notion of cohomological obstruction. I will discuss two recent results:
1) (joint work with Yijin Wang) almost strong approximation for general linear algebraic group (open question of Rapinchuk and Tralle);
2) (joint work with Zhizhong Huang and Runlin Zhang) arithmetic purity of strong approximation for semi-simple simply connected case (open question of Wittenberg).
