Abstract:
A Liouville-type estimate is proved for the irrationality measure of the quantities
$$
\zeta_q(2)
=\sum_{n=1}^\infty\frac{q^n}{(1-q^n)^2}
$$
with $q^{-1}\in\mathbb Z\setminus\{0,\pm1\}$.
The proof is based on the application of a $q$-analogue of the arithmetic method developed by Chudnovsky, Rukhadze, and Hata and of the transformation group for hypergeometric
series–the group-structure approach introduced by Rhin and Viola.