I'm currently self-studying F. Cooper and al.'s *Supersymmetry in Quantum Mechanics*, and I need help working out a particular case on shape-invariance.

From a given superpotential of the form $W(x)=ax^3$, where $a>1$, I can derive the two partner potentials:
$$V_{2,1}=W(x)^2\pm W(x)'=a^2x^6\pm 3ax^2$$
I can also say that $V_1(x)$ and $V_2(x)$ are shape-invariant potentials and write:
$$V_2(x;a_1)=V_1(x;a_2)+R(a_1)$$
where $a_1$ is a set of parameters, $a_2$ is a function of $a_1$ and $R(a_1)$ is independent of $x$.

From there, I am a bit lost. How do I work out the energy spectrum for the first few partner Hamiltonians?

This post imported from StackExchange Physics at 2014-10-23 21:54 (UTC), posted by SE-user Demosthene