Growth rates of subgroups of the free group: density and convergence

Growth rates of subgroups of the free group: density and convergence

Growth rates of subgroups of the free group: density and convergence

Thursday, November 6, 2025
  • Lecturer: Gal Yehuda (Yale)
  • Location: Amado 919
Abstract:

We will talk about growth rates of subgroups of a free group. We prove that for every $\alpha \in [1,2r-1]$ there exists a subgroup $H < F_r$ whose growth rate is \alpha. We also prove a convergence result for the growth rate of the fundamental group of a graph. More precisely, we prove that if G is an (infinite) graph and $ \Gamma = \pi_1(G, v)$, then the growth rate of \Gamma equals the limit of the growth rate of $\Gamm_n := \pi_1(B_n, v)$, where $B_n$ is a ball of radius n around v.

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