Fluctuations of the Gromov–Prohorov sample model

Abstract

In this paper, we study the fluctuations of observables of metric measure spaces which are random discrete approximations ${\mathcal{X}}_n$ of a fixed arbitrary (complete, separable) metric measure space $\mathcal{X}=(\mathcal{X},d,\mathrm{\mu })$. These observables $\mathrm{\Phi }({\mathcal{X}}_n)$ are polynomials in the sense of Greven–Pfaffelhuber–Winter, and we show that for a generic model space $\mathcal{X}$, they yield asymptotically normal random variables. However, if $\mathcal{X}$ is a compact homogeneous space, then the fluctuations of the observables are much smaller, and after an adequate rescaling, they converge towards probability distributions which are not Gaussian. Conversely, we prove that if all the fluctuations of the observables $\mathrm{\Phi }({\mathcal{X}}_n)$ are smaller than in the generic case, then the measure metric space $\mathcal{X}$ is compact homogeneous. The proofs of these results rely on the Gromov reconstruction principle, and on an adaptation of the method of cumulants and mod-Gaussian convergence developed by Féray–Méliot–Nikeghbali. As an application of our results, we construct a statistical test of the hypothesis of symmetry of a compact Riemannian manifold.