Simplices in large sets and directional expansion in ergodic actions
Forum of Mathematics, Sigma, Tome 12 (2024)
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In this paper, we study ergodic $\mathbb {Z}^r$-actions and investigate expansion properties along cyclic subgroups. We show that under some spectral conditions, there are always directions which expand significantly a given measurable set with positive measure. Among other things, we use this result to prove that the set of volumes of all r-simplices with vertices in a set with positive upper density must contain an infinite arithmetic progression, thus showing a discrete density analogue of a classical result by Graham.
@article{10_1017_fms_2024_125,
author = {Michael Bj\"orklund and Alexander Fish},
title = {Simplices in large sets and directional expansion in ergodic actions},
journal = {Forum of Mathematics, Sigma},
publisher = {mathdoc},
volume = {12},
year = {2024},
doi = {10.1017/fms.2024.125},
language = {en},
url = {http://geodesic.mathdoc.fr/articles/10.1017/fms.2024.125/}
}
TY - JOUR AU - Michael Björklund AU - Alexander Fish TI - Simplices in large sets and directional expansion in ergodic actions JO - Forum of Mathematics, Sigma PY - 2024 VL - 12 PB - mathdoc UR - http://geodesic.mathdoc.fr/articles/10.1017/fms.2024.125/ DO - 10.1017/fms.2024.125 LA - en ID - 10_1017_fms_2024_125 ER -
%0 Journal Article %A Michael Björklund %A Alexander Fish %T Simplices in large sets and directional expansion in ergodic actions %J Forum of Mathematics, Sigma %D 2024 %V 12 %I mathdoc %U http://geodesic.mathdoc.fr/articles/10.1017/fms.2024.125/ %R 10.1017/fms.2024.125 %G en %F 10_1017_fms_2024_125
Michael Björklund; Alexander Fish. Simplices in large sets and directional expansion in ergodic actions. Forum of Mathematics, Sigma, Tome 12 (2024). doi: 10.1017/fms.2024.125
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