Painlevé I tau-function connection formula across a B-cycle Stokes jump

Let (ν±,ρ±)(\nu^\pm,\rho^\pm) be two parameter pairs, and let T±(t,ν±,ρ±,)\mathscr T^\pm(t,\nu^\pm,\rho^\pm,\hbar) be analytic τ\tau-functions of (PI)(P_{\rm I}) defined on domains containing t=tc±iϵt=t_c\pm i\epsilon, respectively. Let Li2\operatorname{Li}_2 denote the dilogarithm, and let the negative real axis be the Stokes direction being crossed. Painlevé I tau-function connection conjecture. When tt crosses the negative real axis, the analytic τ\tau-functions satisfy

T(t,ν,ρ,)=exp(12πiLi2(e2πiρ+/))T+(t,ν+,ρ+,),\mathscr T^-(t,\nu^-,\rho^-,\hbar)= \exp\left(\frac{1}{2\pi i}\operatorname{Li}_2\left(e^{2\pi i\rho^+/\hbar}\right)\right) \mathscr T^+(t,\nu^+,\rho^+,\hbar),

where

(ν+,ρ+)=(ν2πilog(1e2πiρ/),ρ).(\nu^+,\rho^+)=\left(\nu^- -\frac{\hbar}{2\pi i}\log\left(1-e^{2\pi i\rho^-/\hbar}\right),\rho^-\right).

This is a nonlinear connection formula relating the two analytic continuations across the Stokes direction; its rigorous status is not established in the supplied text.

Sources & referencesView supporting material

Primary source

Kohei Iwaki, “Les Houches Lectures on Exact WKB Analysis and Painlevé Equations”, arXiv:2512.17599 (2026).

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