The empirical limit measure dimension conjecture for branching random walks on hyperbolic groups

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Let Γ\Gamma be a non-elementary hyperbolic group generated by a finite set SS, and let ν\nu be a probability measure on SS with supp(ν)=S\operatorname{supp}(\nu)=S. Consider the branching random walk on Γ\Gamma with growth rate β>0\beta>0 induced by the random walk with transition probabilities p(x,y)=ν(x1y)p(x,y)=\nu(x^{-1}y). Let v>0v>0 be the almost-sure escape rate, let a>1a>1 be the visual parameter of the boundary metric dad_a on Γ\partial \Gamma, and let μ\mu_\infty be the empirical limit measure on the accumulation set of the branching random walk. Empirical limit measure dimension conjecture. In this setting, almost surely,

dimsuppμ=(βvlog(a))dimΓ.\dim \operatorname{supp} \mu_\infty=\left(\frac{\beta}{v\log(a)}\right)\wedge \dim \partial \Gamma.

This predicts that the dimension of the support of the empirical limit measure is determined by the ratio of the branching growth rate to the random walk's escape rate and the visual scaling parameter, capped by the dimension of the boundary. The claim is proposed for branching random walks on non-elementary hyperbolic groups; the source does not state a resolution.

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Primary source

David Geldbach, “Hyperbolic branching Brownian motion: the empirical limit measure”, arXiv:2509.06730 (2026).

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