Third-order affine-invariant (systems of) PDEs in two independent variables as vanishing of the Fubini-Pick invariant

TL;DR

This paper investigates third-order PDE systems in two variables that are invariant under affine transformations, linking them to the Fubini-Pick invariant and using a general method to derive these equations, revealing their geometric significance.

Contribution

It introduces a new class of affine-invariant third-order PDEs in two variables, connecting them to the Fubini-Pick invariant and applying a novel derivation method.

Findings

Established the relationship between the PDEs and the Fubini-Pick invariant.

Derived the PDEs using a general invariant construction method.

Explored the geometric properties of the invariant PDEs.

Abstract

In this paper we study $3^{\mathrm{rd}}$ order (system of) PDEs in two independent variables $x,y$ and one unknown function $u$ that are invariant with respect to the group of affine transformation $\mathrm{Aff}(3)$ of $\mathbb{R}^3=\{(x,y,u)\}$. After proving their relationship with the Fubini-Pick invariant, we derive the aforementioned PDEs by using a general method introduced in [D.V. Alekseevsky, J. Gutt, G. Manno, and G. Moreno: A general method to construct invariant {PDEs} on homogeneous manifolds. Communications in Contemporary Mathematics (2021)], which sheds light on some of their geometrical properties.