A $3\times3$ linear $q$-difference system with $E_8^{(1)}$-symmetry
Takahiko Nobukawa
TL;DR
The paper constructs a rank-$3$ linear $q$-difference equation with the affine Weyl group symmetry of type $E_8^{(1)}$, realized via a $q$-middle convolution implemented through a $q$-Okubo reformulation. The main result, Theorem E8mc, provides a birational transformation of the equation’s parameters under $q$-middle convolution, yielding a concrete $W(E_8^{(1)})$-action generated by a distinguished $s_0$ and adjacent transpositions. The rank-$3$ system is shown to reduce to a scalar, non-autonomous version of Moriyama–Yamada’s quantum curve MY, establishing a link to quantum Painlevé-type dynamics and suggesting connections to quantum integrable systems. The work thus integrates geometric Weyl-group symmetries, $q$-convolution techniques, and scalar reductions to illuminate higher-symmetry $q$-difference equations and their potential Lax structures and degenerations.
Abstract
We present a linear $q$-difference equation of rank $3$, which admits the affine Weyl group symmetry of type $E_8^{(1)}$. We further compare this equation with Moriyama-Yamada's quantum curve which has $W(E_8^{(1)})$-symmetry. The symmetry of our equation is provided by the $q$-middle convolution, defined by Sakai-Yamaguchi and reformulated by Arai-Takemura. In this paper, we provide a reconstruction of the $q$-middle convolution via a $q$-Okubo type equation.
