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Title: Acylindrical actions on trees and applications to the outer automorphism group of Baumslag-Solitar groups

Abstract: An acylindrical action generalizes proper and cobounded actions on hyperbolic spaces. Non-elementary acylindrical actions provide acylindrically hyperbolic groups, which includes most mapping class groups of punctured surfaces, 3-manifold groups, and Out(F_n) for n > 1. In this talk, we will explore how acylindricity of a group action on a tree can be preserved under quotients by certain subgroups, and discuss the existence of a largest acylindrical action for some groups acting on trees. In addition, we will show when Out(BS(p,q)) is acylindrically hyperbolic for non-solvable Baumslag-Solitar groups, despite BS(p,q) itself not being acylindrically hyperbolic, and explore further applications of these acylindricity results. This is a joint work with Daxun Wang.

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After the talk we will gather in the lounge for tea and snacks and then we will have dinner with Bratati.