From Euclidean to Minkowski space with the Cauchy–Riemann equations Mercedes Gimeno-Segovia and Felipe J. Llanes-Estrada Eur. Phys. J. C, 56 4 (2008) 557-569 Published online: 05 August 2008 DOI: 10.1140/epjc/s10052-008-0676-5