This paper considers a generalised Strum-Liouville equation, that is equations of the form
$$ \left[-\frac{d}{dx}p(x)\frac{d}{dx}-\frac{i}{2}\left(\lambda_1(x)\frac{d}{dx}+\frac{d}{dx}\lambda_2(x)\right)+v(x)\right]\psi(x)=\left(\frac{\omega}{c}\right)^2\psi(x)\tag{1} $$
and calls $\lambda_i(x)\in\mathbb{C}$ complex gauge potentials. What do these potentials represent physically?
In particular I'm interested in the case where $p(x)$ is constant and $v(x)=0$ so that $\psi(x)$ represents some kind of time harmonic wave equation.