Advanced Quantum Mechanics Schwabl · Problem 13.18

Quantization of the Radiation Field

Physics — Quantum Mechanics · feynman-fermion-propagator

Problem

Prove equation (13.4.15). Hint: Use

\delta\left(k^2 - m^2\right) = \left(\delta\left(k^0 - \sqrt{\mathbf{k}^2+m^2}\right) + \delta\left(k^0 + \sqrt{\mathbf{k}^2+m^2}\right)\right)\big/\sqrt{\mathbf{k}^2+m^2}\,.