Haag's theorem

Rudolf Haag showed in 1955 that the interaction picture cannot be rigorously defined in quantum field theory, a result now commonly cited as Haag's Theorem. This is in stark contrast to the successes of perturbative quantum electrodynamics.

Related Topics:
Rudolf Haag - Interaction picture - Quantum field theory - Quantum electrodynamics

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Citing the formulation used by Arageorgis:

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• If two pure ground states are not equal, then they generate unitarily inequivalent irreducible representations.
• If two local quantum fields are unitarily equivalent at any given time, then both fields are free if one of them is free.
 
Haag's theorem: References ►