Energy level displacement of the excited $n\ell$ state of pionic hydrogen

The energy level displacements of the excited states of pionic hydrogen and the contribution of the transitions and the transitions of the pair, coupled by the attractive Coulomb field in the S-wave state with a continuous energy spectrum, to the shift of the energy level of the ground state of pionic hydrogen, caused by strong low-energy interactions, are calculated within a quantum field theoretic, relativistic covariant and model-independent approach.Received: 19 November 2003, Revised: 25 November 2003, Published online: 5 February 2004PACS: 13.75.Gx Pion-baryon interactions - 11.10.St Bound and unstable states; Bethe-Salpeter equations - 21.30.Fe Forces in hadronic systems and effective interactions - 31.15.Ar Ab initio calculationsPermanent address A.N. Ivanov: State Polytechnical University, Department of Nuclear Physics, 195251 St. Petersburg, Russian Federation;Permanent address N.I. Troitskaya: State Polytechnical University, Department of Nuclear Physics, 195251 St. Petersburg, Russian Federation.