English

Hyper-regular graphs and high dimensional expanders

Combinatorics 2023-08-28 v3 Group Theory

Abstract

Let G=(V,E)G= (V,E) be a finite graph. For d0>0d_0>0 we say that GG is d0d_0-regular, if every vVv\in V has degree d0d_0. We say that GG is (d0,d1)(d_0, d_1)-regular, for 0<d1<d00<d_1<d_0, if GG is d0d_0 regular and for every vVv\in V, the subgraph induced on vv's neighbors is d1d_1-regular. Similarly, GG is (d0,d1,,dn1)(d_0, d_1,\ldots, d_{n-1})-regular for 0<dn1<<d1<d00<d_{n-1}<\ldots<d_1<d_0, if GG is d0d_0 regular and for every 1in11\leq i\leq n-1, the joint neighborhood of every clique of size ii is did_i-regular; In that case, we say that GG is an nn-dimensional hyper-regular graph (HRG). Here we define a new kind of graph product, through which we build examples of infinite families of nn-dimensional HRG such that the joint neighborhood of every clique of size at most n1n-1 is connected. In particular, relying on the work of Kaufman and Oppenheim, our product yields an infinite family of nn-dimensional HRG for arbitrarily large nn with good expansion properties. This answers a question of Dinur regarding the existence of such objects.

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Cite

@article{arxiv.2010.03829,
  title  = {Hyper-regular graphs and high dimensional expanders},
  author = {Ehud Friedgut and Yonatan Iluz},
  journal= {arXiv preprint arXiv:2010.03829},
  year   = {2023}
}

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27 pages