Graded colour Lie superalgebras for solving L\'evy-Leblond equations

The L\'evy-Leblond equation with free potential admits a symmetry algebra that is a $\mathbb{Z}_2\times\mathbb{Z}_2$-graded colour Lie superalgebra (see arXiv:1609.08224). We extend this result in two directions by considering a time-independent version of the L\'evy-Leblond equation. First, we construct a $\mathbb{Z}_2^3$-graded colour Lie superalgebra containing operators that leave the eigenspaces invariant and demonstrate the utility of this algebra in constructing general solutions for the free equation. Second, we find that the ladder operators for the harmonic oscillator generate a $\mathbb{Z}_2\times\mathbb{Z}_2$-graded colour Lie superalgebra and we use the operators from this algebra to compute the spectrum. These results illustrate two points: the L\'evy-Leblond equation admits colour Lie superalgebras with gradings higher than $\mathbb{Z}_2\times\mathbb{Z}_2$ and colour Lie superalgebras appear for potentials besides the free potential.