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  1. Inspired by results of Eskin and Mirzakhani (J Mod Dyn 5(1):71–105, 2011) counting closed geodesics of length at most L in the moduli space of a fixed closed surface, we consider a similar question in the Out(Fr) setting. The Eskin-Mirzakhani result can be equivalently stated in terms of counting the number of conjugacy classes (within the mapping class group) of pseudo-Anosovs whose dilatations have natural logarithm at most L. Let N(L) denote the number of Out(Fr)-conjugacy classes of fully irreducibles satisfying that the natural logarithm of their dilatation is at most L. We prove for r>2 that as L goes to infinity, the number N(L) has double exponential (in L) lower and upper bounds. These bounds reveal behavior not present in the surface setting or in classical hyperbolic dynamical systems. 
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    Free, publicly-accessible full text available April 1, 2025
  2. Abstract In this article, we propose an Outer space analog for the principal stratum of the unit tangent bundle to the Teichmüller space ${\mathcal{T}}(S)$ of a closed hyperbolic surface $S$. More specifically, we focus on properties of the geodesics in Teichmüller space determined by the principal stratum. We show that the analogous Outer space “principal” periodic geodesics share certain stability properties with the principal stratum geodesics of Teichmüller space. We also show that the stratification of periodic geodesics in Outer space exhibits some new pathological phenomena not present in the Teichmüller space context. 
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