Systems of partial differential equations describing pseudo-spherical or spherical surfaces

TL;DR

This paper classifies nonlinear PDE systems describing surfaces of constant curvature, providing new examples and solutions, and analyzing their geometric and symmetry properties.

Contribution

It offers a classification of Camassa-Holm-type systems related to pseudospherical surfaces, including new examples and symmetry analysis.

Findings

Classified systems describing pseudospherical and spherical surfaces.

Constructed new examples like the Song-Qu-Qiao and modified Camassa-Holm systems.

Derived nonlocal symmetries and solutions from spectral parameters.

Abstract

In this paper, we study systems of nonlinear partial differential equations which describe surfaces of constant curvature. From the flatness condition of connection 1-forms, we present a classification of systems of Camassa-Holm-type equations of the form \begin{equation*} \left\{ \begin{aligned} u_{t} - u_{xxt} &= F(x, t, u, u_{x}, \dots, \partial ^{m} u/\partial _x^{m}, v, v_{x}, \dots, \partial ^{n} v/\partial _x^{n}), \\ v_{t} - v_{xxt} &= G(x, t, u, u_{x}, \dots, \partial ^{m} u/\partial _x^{m}, v, v_{x}, \dots, \partial ^{n} v/\partial _x^{n}), \end{aligned} \right. \end{equation*} with $m,n\geq2$, for $F$ and $G$ smooth functions, describing pseudospherical or spherical surfaces. We also establish classification results for a special type of third-order system. Applications of the results provide new examples of such systems, such as the Song-Qu-Qiao system, the two-component Camassa-Holm system with cubic nonlinearity, and the modified Camass-Holm-type system. Moreover, we construct the nonlocal symmetry and a non-trivial solutions for the two-component Camassa-Holm system with cubic nonlinearity from the gradients of spectral parameters.