Congruence counting in Schottky and continued fractions semigroups of $\operatorname{SO}(n, 1)$

Fuente: arXiv
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Main Author: Sarkar, Pratyush
Format: Preprint
Published: 2021
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author Sarkar, Pratyush
author_facet Sarkar, Pratyush
contents In this paper, the two settings we are concerned with are $Γ< \operatorname{SO}(n, 1)$ a Zariski dense Schottky semigroup and $Γ< \operatorname{SL}_2(\mathbb C)$ a Zariski dense continued fractions semigroup. In both settings, we prove a uniform asymptotic counting formula for the associated congruence subsemigroups, generalizing the work of Magee-Oh-Winter [arXiv:1601.03705] in $\operatorname{SL}_2(\mathbb R)$ to higher dimensions. Superficially, the proof requires two separate strategies: the expander machinery of Golsefidy-Varjú, based on the work of Bourgain-Gamburd-Sarnak, and Dolgopyat's method. However, there are several challenges in higher dimensions. Firstly, using the expander machinery requires a key input: the Zariski density and full trace field property of the return trajectory subgroups, newly introduced in [arXiv:2006.07787]. Secondly, we need to adapt Stoyanov's version of Dolgopyat's method to circumvent some technical issues while the main difficulty is to prove the key inputs: the local non-integrability condition (LNIC) and the non-concentration property (NCP).
format Preprint
id arxiv_https___arxiv_org_abs_2108_00545
institution arXiv
publishDate 2021
record_format arxiv
spellingShingle Congruence counting in Schottky and continued fractions semigroups of $\operatorname{SO}(n, 1)$
Sarkar, Pratyush
Number Theory
Dynamical Systems
Spectral Theory
22E40, 37A44, 37C30
In this paper, the two settings we are concerned with are $Γ< \operatorname{SO}(n, 1)$ a Zariski dense Schottky semigroup and $Γ< \operatorname{SL}_2(\mathbb C)$ a Zariski dense continued fractions semigroup. In both settings, we prove a uniform asymptotic counting formula for the associated congruence subsemigroups, generalizing the work of Magee-Oh-Winter [arXiv:1601.03705] in $\operatorname{SL}_2(\mathbb R)$ to higher dimensions. Superficially, the proof requires two separate strategies: the expander machinery of Golsefidy-Varjú, based on the work of Bourgain-Gamburd-Sarnak, and Dolgopyat's method. However, there are several challenges in higher dimensions. Firstly, using the expander machinery requires a key input: the Zariski density and full trace field property of the return trajectory subgroups, newly introduced in [arXiv:2006.07787]. Secondly, we need to adapt Stoyanov's version of Dolgopyat's method to circumvent some technical issues while the main difficulty is to prove the key inputs: the local non-integrability condition (LNIC) and the non-concentration property (NCP).
title Congruence counting in Schottky and continued fractions semigroups of $\operatorname{SO}(n, 1)$
topic Number Theory
Dynamical Systems
Spectral Theory
22E40, 37A44, 37C30
url https://arxiv.org/abs/2108.00545