Non-relativistic Bremsstrahlung in QED: Hamiltonian vs. Path Integral   Approach
  An alternative derivation of the radiation intensity in non-relativistic bremsstrahlung is provided utilizing the path integral formalism. By integrating out the gauge field, one obtains the effective action which it's imaginary part is interpreted as the rate of photon production during the collision. 
A. Jahan
quant-ph