A sharper threshold for random groups at density one-half

作者：Duchin Moon^*; Jankiewicz Kasia; Kilmer Shelby C; Lelievre Samuel; Mackay John M; Sanchez Andrew P

来源：Groups, Geometry, and Dynamics, 2016, 10(3): 985-1005.

DOI：10.4171/GGD/374

• Random groups
• hyperbolic groups
• density model
• triviality threshold

In the theory of random groups, we consider presentations with any fixed number m of generators and many random relators of length l, sending l -> infinity. If d is a density parameter measuring the rate of exponential growth of the number of relators compared to the length of relators, then many group-theoretic properties become generically true or generically false at different values of d. The signature theorem for this density model is a phase transition from triviality to hyperbolicity: for d < 1/2, random groups are a.a.s. infinite hyperbolic, while for d > 1/2, random groups are a.a.s. order one or two. We study random groups at the density threshold d = 1/2. Kozma had found that trivial groups are generic for a range of growth rates at d = 1/2; we show that infinite hyperbolic groups are generic in a different range. (We include an exposition of Kozma's previously unpublished argument, with slightly improved results, for completeness.)

• 出版日期2016