ANTCoG seminar: Talia Fernós

Talia Fernós, Visiting Professor at Vanderbilt University and Professor in the Department of Mathematics at University of North Carolina, Greensboro (on leave)

Title: The semi-simple theory of acylindricity in higher-rank

Abstract: 

Acylindricity may be viewed as a generalization of being a uniform lattice in a locally compact second countable group. The recent surge of results concerning acylindrical actions on hyperbolic spaces demonstrates the utility of the property. Trees are of course examples of hyperbolic spaces, and by considering products, we start to see new and interesting behaviors that are not present in rank-1, such as the simple Burger-Mozes-Wise lattices, or Bestvina-Brady kernels. 

In a joint worth with S. Balasubramanya we introduce a new class of nonpositively curved groups. Viewing the theory of S-arithmetic semi-simple lattices as inspiration, we extend the theory of acylindricity to higher rank and consider finite products of delta-hyperbolic spaces. The category is closed under products, subgroups, and finite index over-groups. Weakening acylindricity to AU-acylindricity (i.e. acylindricity of Ambiguous Uniformity) the theory captures all S-arithmetic semi-simple lattices with rank-1 factors, acylindrically hyperbolic groups, colorable HHGs, and many others. 

In this talk, we will discuss the Tits’ alternative and deduce that a group G that admits an (unbounded) AU-acylindrical action on such a product is “semi-simple” from the point of Out(G), thereby giving a partial resolution to a recent conjecture by Sela.