On nets of local algebras on ℤ 4 , covariant with respect to the discrete Poincaré group ; causality and scattering theory Hellmut Baumgärtel — 1988 Annales de l'I.H.P. Physique théorique
On the structure of relative identification operators for quantum fields and their connection with the Haag-Ruelle scattering theory Hellmut Baumgärtel — 1984 Annales de l'I.H.P. Physique théorique