Gradients of sequences of subgroups in a direct product

Author: 

Nikolov, N
Shemtov, Z
Shusterman, M

Publication Date: 

9 October 2017

Journal: 

International Mathematics Research Notices

Last Updated: 

2019-07-05T22:47:31.097+01:00

DOI: 

10.1093/imrn/rnx236

abstract: 

For a sequence $\{U_n\}_{n = 1}^\infty$ of finite index subgroups of a direct
product $G = A \times B$ of finitely generated groups, we show that $$\lim_{n
\to \infty} \frac{\min\{|X| : \langle X \rangle = U_n\}}{[G : U_n]} = 0$$ once
$[A : A \cap U_n], [B : B \cap U_n] \to \infty$ as $n \to \infty$. Our proof
relies on the classification of finite simple groups. For $A,B$ that are
finitely presented we show that $$ \lim_{n \to \infty} \frac{\log
|\mathrm{Torsion}(U_n^{\mathrm{ab}})|}{[G : U_n]} = 0. $$

Symplectic id: 

648395

Download URL: 

Submitted to ORA: 

Submitted

Publication Type: 

Journal Article