Borchers property

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The Borchers property is a property of local nets in the Haag-Kastler approach to quantum field theory that follows, by a theorem of Borchers, from three physically motivated axioms on local nets. If every local algebra of the net is a type III factor, then the Borchers property is also a direct consequence.

The Borchers property is therefore often used as an “intermediate technical assumption”.

Sometimes this property is also abbreviated as “property B”.


Let (𝒪)\mathcal{M}(\mathcal{O}) be a net of von Neumann algebras indexed by bounded open subsets of Minkowski spacetime, for more details see Haag-Kastler vacuum representation,


The net (𝒪)\mathcal{M}(\mathcal{O}) satisfies the Borchers property if for every double cones K 1,K 2K_1, K_2 with K¯ 1K 2\bar K_1 \subseteq K_2 and E(𝒦 1)E \in \mathcal{M}(\mathcal{K}_1) a nonzero projection, EE is (Murray-von Neumann) equivalent to the identity with respect to (𝒦 2)\mathcal{M}(\mathcal{K}_2). That is, there is a partial isometry V(𝒦 2)V \in \mathcal{M}(\mathcal{K}_2) such that VV *=E,V *V=𝟙VV^* = E, V^*V = \mathbb{1}.



A net satisfying causality, the spectrum condition and weak additivity (see Haag-Kastler vacuum representation for definitions) satisfies the Borchers property.

Remark : In particular the local algebras of nets that satisfy the Borchers property cannot be finite where finite is meant in the sense of the Murray-von Neumann classification of factors.


  • H.-J. Borchers: A remark on a theorem of B. Misra (available online from project euclid here)

Revised on June 30, 2010 10:42:23 by Tim van Beek (