Source: wikibot/haag-s-theorem
= Haag's theorem
{wiki=Haag's_theorem}
Haag's theorem is a result in quantum field theory that addresses the challenges of interacting quantum field theories. It was formulated by Res Jost and, independently, by Res Jost and Lothar Haag in the 1950s. The theorem shows that the interaction picture, commonly used to describe dynamical processes in quantum field theory, is not well-defined for interacting quantum fields.