Properties of Hesse derivatives of cubic curves

TL;DR

This paper explores the properties of Hesse derivatives of cubic curves, revealing geometric relationships, fixed points, and the dynamical system behavior induced by the Hesse operator on these curves.

Contribution

It introduces a detailed geometric analysis of Hesse derivatives, identifies fixed points, and studies the iterative dynamical system they generate on cubic curves.

Findings

Contact points lie on lines intersecting the original and Hesse curves.

Fixed points of the dynamical system are characterized.

Closed orbits and orbit behavior are discussed.

Abstract

The Hesse curve or Hesse derivative Hess$(\Gamma_f)$ of a cubic curve $\Gamma_{f}$ given by a homogeneous polynomial $f$ is the set of points $P$ such that $\det \left(H_f (P)\right)=0$, where $H_f (P)$ is the Hesse matrix of $f$ evaluated at $P$. Also Hess$(\Gamma_f)$ is again a cubic curve. We show that for a point $P\in$Hess$(\Gamma_{f})$, all the contact points of tangents from $P$ to the curves $\Gamma_{f}$ and Hess$(\Gamma_{f})$ are intersection points of two straight lines $\ell_1^P$ and $\ell_2^P$ (meeting on Hess$(\Gamma_{f})$) with $\Gamma_{f}$ and Hess$(\Gamma_{f})$, where the product of $\ell_1^P$ and $\ell_2^P$ is the polar conic of $\Gamma_{f}$ at $P$. The operator Hess defines an iterative discrete dynamical system on the set of the cubic curves. We identify the two fixed points of this system, investigate orbits that end in the fixed points, and discuss the closed orbits of the dynamical system.