Quasi-isometric embeddings of Ramanujan complexes

Fuente: arXiv
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Main Author: Choi, Hyein
Format: Preprint
Published: 2025
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author Choi, Hyein
author_facet Choi, Hyein
contents Ramanujan complexes were defined as high dimensional analogues of the optimal expanders, Ramanujan graphs. They were constructed as quotients of the Euclidean building (also called the affine building and the Bruhat-Tits building) of $\mathrm{PGL}_d(\mathbb{F}_p((y)))$ by certain cocompact lattices by Lubotzky-Samuels-Vishne. We distinguish the Ramanujan complexes up to large-scale geometry. More precisely, we show that if $p$ and $q$ are distinct primes, then the associated Ramanujan complexes do not quasi-isometrically embed into one another. The main tools are the box space rigidity of Khukhro-Valette and the Euclidean building rigidity of Kleiner-Leeb and Fisher-Whyte.
format Preprint
id arxiv_https___arxiv_org_abs_2506_23585
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Quasi-isometric embeddings of Ramanujan complexes
Choi, Hyein
Group Theory
Combinatorics
Metric Geometry
Ramanujan complexes were defined as high dimensional analogues of the optimal expanders, Ramanujan graphs. They were constructed as quotients of the Euclidean building (also called the affine building and the Bruhat-Tits building) of $\mathrm{PGL}_d(\mathbb{F}_p((y)))$ by certain cocompact lattices by Lubotzky-Samuels-Vishne. We distinguish the Ramanujan complexes up to large-scale geometry. More precisely, we show that if $p$ and $q$ are distinct primes, then the associated Ramanujan complexes do not quasi-isometrically embed into one another. The main tools are the box space rigidity of Khukhro-Valette and the Euclidean building rigidity of Kleiner-Leeb and Fisher-Whyte.
title Quasi-isometric embeddings of Ramanujan complexes
topic Group Theory
Combinatorics
Metric Geometry
url https://arxiv.org/abs/2506.23585