Abstract:
We extend the relation between cluster integrable systems and $q$-difference equations beyond the Painlevé case. We consider the class of hyperelliptic curves where the Newton polygons contain only four boundary points. We present the corresponding cluster integrable Toda systems and identify their discrete automorphisms with certain reductions of the Hirota difference equation. We also construct nonautonomous versions of these equations and find that their solutions are expressed in terms of five-dimensional Nekrasov functions with Chern–Simons contributions, while these equations in the autonomous case are solved in terms of Riemann theta functions.
The main results obtained in Sec. 2 were supported
by a grant from the Russian Science Foundation (Project No. 16-11-10160).
The research of A. V. Marshakov was supported in
part by the Russian Foundation for Basic research (Grant No. 17-01-00585)
and an RFBR/JSPS joint project (Grant No. 17-51-50051).
This research was also supported by the Russian Academic
Excellence Project "5-100."
M. A. Bershtein and P. G. Gavrylenko are Young Russian
Mathematics award winners and thank its sponsors and jury.
Citation:
M. A. Bershtein, P. G. Gavrilenko, A. V. Marshakov, “Cluster Toda chains and Nekrasov functions”, TMF, 198:2 (2019), 179–214; Theoret. and Math. Phys., 198:2 (2019), 157–188