On pionic hydrogen. Quantum field theoretic, relativistic covariant and model-independent approach A. N. Ivanov, M. Faber, A. Hirtl, J. Marton and N. I. Troitskaya Eur. Phys. J. A, 18 4 (2003) 653-666 Published online: 02 December 2003 DOI: 10.1140/epja/i2003-10095-1