Nonuniqueness of the $λΦ^4$-vacuum

Abstract

We prove that the massless neutral $λΦ^4$-theory does not possess a unique vacuum. Based on the Wightman axioms the non-existence of a state which preserves Poincar{é} and scale invariance is demonstrated non-perturbatively for a non-vanishing self-interaction. We conclude that it is necessary to break the scale invariance in order to define a vacuum state. The renormalized vacuum expectation value of the energy-momentum tensor is derived from the two-point Wightman function employing the point-splitting technique and its relation to the phionic and the scalar condensate is addressed. Possible implications to other self-interacting field theories and to different approaches in quantum field theory are pointed out. PACS: 11.10.Cd, 11.15.Tk, 11.30.Qc