Morse index for figure-eight choreographies of the planar equal mass three-body problem

TL;DR

This paper numerically investigates the Morse index of figure-eight choreographies in the three-body problem with various potentials, revealing how the index varies with potential parameters and linking it to solution stability and bifurcations.

Contribution

It provides the first detailed numerical analysis of Morse indices for figure-eight solutions under homogeneous and Lennard-Jones potentials, elucidating their stability properties.

Findings

Morse index varies with potential parameter a, showing distinct regimes.

For a=1, a strong relationship between figure-eight and periodic solutions is established.

In Lennard-Jones systems, Morse indices increase monotonically with period T, indicating changing stability.

Abstract

We report on numerical calculations of Morse index for figure-eight choreographic solutions to a system of three identical bodies in a plane interacting through homogeneous potential, $-1/r^a$, or through Lennard-Jones-type (LJ) potential, $1/r^{12} - 1/r^6$, where $r$ is a distance between the bodies. The Morse index is a number of independent variational functions giving negative second variation $S^{(2)}$ of action functional $S$. We calculated three kinds of Morse indices, $N$, $N_c$ and $N_e$, in the domain of the periodic, the choreographic and the figure-eight choreographic function, respectively. For homogeneous system, we obtain $N=4$ for $0 \le a < a_0$, $N=2$ for $a_0 < a < a_1$, $N=0$ for $a_1 < a$, and $N_c=N_e=0$ for $0 \le a$, where $a_0=0.9970$ and $a_1=1.3424$. For $a=1$, we show a strong relationship between the figure-eight choreography and the periodic solution found by Sim\'{o} through the $S^{(2)}$. For LJ system, we calculated the index for the solution tending to the figure-eight solution of $a=6$ homogeneous system for the period $T \to \infty$. We obtain $N$, $N_c$ and $N_e$ as monotonically increasing functions of the gradual change in $T$ from $T \to \infty$, which start with $N=N_c=N_e=0$, jump at the smallest $T$ by $1$, and reach $N=12$, $N_c=4$, and $N_e=1$ for $T \to \infty$ in the other branch.