# Compacton equations and integrability: the Rosenau-Hyman and Cooper-Shepard-Sodano equations

## TL;DR

This paper classifies integrable compacton equations, provides their recursion operators, and shows their relation to the Korteweg-de Vries equation, also constructing isochronous hierarchies for the integrable cases.

## Contribution

It offers a complete classification of integrable $K(m,n)$ and $CSS$ equations, including their recursion operators and connections to the KdV equation.

## Key findings

- All integrable equations are related to the KdV equation via nonlocal transformations.
- Recursion operators for the classified equations are explicitly constructed.
- Isochronous hierarchies are developed for the integrable $CSS$ equations.

## Abstract

We study integrability --in the sense of admitting recursion operators-- of two nonlinear equations which are known to possess compacton solutions: the $K(m,n)$ equation introduced by Rosenau and Hyman \[ D_t(u) + D_x(u^m) + D_x^3(u^n) = 0 \; , \] and the $CSS$ equation introduced by Coooper, Shepard, and Sodano, \[ D_t(u) + u^{l-2}D_x(u) + \alpha p D_x (u^{p-1} u_x^2) + 2\alpha D_x^2(u^p u_x) = 0 \; . \] We obtain a full classification of {\em integrable $K(m,n)$ and $CSS$ equations}; we present their recursion operators, and we prove that all of them are related (via nonlocal transformations) to the Korteweg-de Vries equation. As an application, we construct isochronous hierarchies of equations associated to the integrable cases of $CSS$.