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| Format: | Preprint |
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2025
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| Online-Zugang: | https://arxiv.org/abs/2504.08988 |
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| _version_ | 1866908342240149504 |
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| author | Magee, Michael Puder, Doron van Handel, Ramon |
| author_facet | Magee, Michael Puder, Doron van Handel, Ramon |
| contents | Let $Γ$ be the fundamental group of a closed orientable surface of genus at least two. Consider the composition of a uniformly random element of $\mathrm{Hom}(Γ,S_n)$ with the $(n-1)$-dimensional irreducible representation of $S_n$. We prove the strong convergence in probability as $n\to\infty$ of this sequence of random representations to the regular representation of $Γ$.
As a consequence, for any closed hyperbolic surface $X$, with probability tending to one as $n\to\infty$, a uniformly random degree-$n$ covering space of $X$ has near optimal relative spectral gap -- ignoring the eigenvalues that arise from the base surface $X$.
To do so, we show that the polynomial method of proving strong convergence can be extended beyond rational settings.
To meet the requirements of this extension we prove two new kinds of results. First, we show there are effective polynomial approximations of expected values of traces of elements of $Γ$ under random homomorphisms to $S_n$. Secondly, we estimate the growth rates of probabilities that a finitely supported random walk on $Γ$ is a proper power after a given number of steps. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_08988 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Strong convergence of uniformly random permutation representations of surface groups Magee, Michael Puder, Doron van Handel, Ramon Geometric Topology Group Theory Operator Algebras Probability Spectral Theory 58J50, 57M10, 20F65, 60B20, 15B52, 46L53 (Primary) 20P05, 20C30, 20B30 (Secondary) Let $Γ$ be the fundamental group of a closed orientable surface of genus at least two. Consider the composition of a uniformly random element of $\mathrm{Hom}(Γ,S_n)$ with the $(n-1)$-dimensional irreducible representation of $S_n$. We prove the strong convergence in probability as $n\to\infty$ of this sequence of random representations to the regular representation of $Γ$. As a consequence, for any closed hyperbolic surface $X$, with probability tending to one as $n\to\infty$, a uniformly random degree-$n$ covering space of $X$ has near optimal relative spectral gap -- ignoring the eigenvalues that arise from the base surface $X$. To do so, we show that the polynomial method of proving strong convergence can be extended beyond rational settings. To meet the requirements of this extension we prove two new kinds of results. First, we show there are effective polynomial approximations of expected values of traces of elements of $Γ$ under random homomorphisms to $S_n$. Secondly, we estimate the growth rates of probabilities that a finitely supported random walk on $Γ$ is a proper power after a given number of steps. |
| title | Strong convergence of uniformly random permutation representations of surface groups |
| topic | Geometric Topology Group Theory Operator Algebras Probability Spectral Theory 58J50, 57M10, 20F65, 60B20, 15B52, 46L53 (Primary) 20P05, 20C30, 20B30 (Secondary) |
| url | https://arxiv.org/abs/2504.08988 |