English

Super approximation for $\text{SL}_2\times \text{SL}_2$ and $\text{ASL}_2$

Group Theory 2026-05-05 v5 Combinatorics Dynamical Systems Number Theory

Abstract

Let SSL2(Z)×SL2(Z)S\subset \text{SL}_2(\mathbb Z)\times \text{SL}_2(\mathbb Z) or SL2(Z)Z2\text{SL}_2(\mathbb Z)\ltimes \mathbb Z^2 be finite symmetric and assume SS generates a group GG which is a Zariski-dense subgroup SL2(Z)×SL2(Z)\text{SL}_2(\mathbb Z)\times \text{SL}_2(\mathbb Z) or SL2(Z)Z2\text{SL}_2(\mathbb Z)\ltimes \mathbb Z^2. We prove that the Cayley graphs {Cay(G(mod q),S(mod q))}qZ\{\mathcal Cay(G(\text{mod } q), S (\text{mod } q))\}_{q\in \mathbb Z} form a family of expanders.

Keywords

Cite

@article{arxiv.2308.09982,
  title  = {Super approximation for $\text{SL}_2\times \text{SL}_2$ and $\text{ASL}_2$},
  author = {Jincheng Tang and Xin Zhang},
  journal= {arXiv preprint arXiv:2308.09982},
  year   = {2026}
}

Comments

Minor revision of previous version

R2 v1 2026-06-28T11:59:21.996Z