The Picard–Fuchs equation in classical and quantum physics: application to higher-order WKB method

The Picard–Fuchs equation is a powerful mathematical tool which has numerous applications in physics, for it allows one to evaluate integrals without resorting to direct integration techniques. We use this equation to calculate both the classical action and the higher-order WKB corrections to it, for the sextic double-well potential and the Lamé potential. Our development rests on the fact that the Picard–Fuchs method links an integral to solutions of a differential equation with the energy as a parameter. Employing the same argument we show that each higher-order correction in the WKB series for the quantum action is a combination of the classical action and its derivatives. From this, we obtain a computationally simple method of calculating higher-order quantum-mechanical corrections to the classical action, and demonstrate this by calculating the second-order correction for the sextic and the Lamé potential. This paper also serves as a self-consistent guide to the use of the Picard–Fuchs equation. (paper)