The focusing complex mKdV equation with nonzero background: Large $N$-order asymptotics of multi-rational solitons and related Painlev\'{e}-III hierarchy

TL;DR

This paper analyzes the large-order asymptotics of multi-rational solitons in the focusing complex mKdV equation with nonzero background, revealing connections to Painlevé-III hierarchy and providing insights into their behavior.

Contribution

It constructs a Riemann-Hilbert problem-based framework for multi-rational solitons and links their large-order asymptotics to Painlevé-III equations, advancing understanding of nonlinear wave solutions.

Findings

Established existence and uniqueness of the limit function RHP.

Identified the limit function with Painlevé-III hierarchy members.

Analyzed large $X$ asymptotics and transitional behaviors.

Abstract

In this paper, we investigate the large-order asymptotics of multi-rational solitons of the focusing complex modified Korteweg-de Vries (c-mKdV) equation with nonzero background via the Riemann-Hilbert problems. First, based on the Lax pair, inverse scattering transform, and a series of deformations, we construct a multi-rational soliton of the c-mKdV equation via a solvable Riemann-Hilbert problem (RHP). Then, through a scale transformation, we construct a RHP corresponding to the limit function which is a new solution of the c-mKdV equation in the rescaled variables $X,\,T$, and prove the existence and uniqueness of the RHP's solution. Moreover, we also find that the limit function satisfies the ordinary differential equations (ODEs) with respect to space $X$ and time $T$, respectively. The ODEs with respect to space $X$ are identified with certain members of the Painlev\'{e}-III hierarchy. We study the large $X$ and transitional asymptotic behaviors of near-field limit solutions, and we provide some part results for the case of large $T$. These results will be useful to understand and apply the large-order rational solitons in the nonlinear wave equations.