nLab cohomology in a local net of observables




algebraic quantum field theory (perturbative, on curved spacetimes, homotopical)



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quantum mechanical system, quantum probability

free field quantization

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In the AQFT formalization of quantum field theory a system is characterized by its local net of observables on spacetime, which is in particular a copresheaf of algebras. Accordingly, one can consider notions of cohomology with coefficients in such a local net.

One such notion was introduced in (Roberts 76), there called local cohomology or net cohomology. It has been shown to encode the DHR superselection theory of local nets (Roberts 90).


Original articles

The concept was first poposed around

  • John RobertsLocal cohomology and superselection structure Comm. Math. Phys. Volume 51, Number 2 (1976), 107-119 (EUCLID)

  • John Roberts, Mathematical Aspects of Local Cohomology talk at Colloqiumon Operator Algebras and their Applications to Mathematical Physics, Marseille 20-24 June, (1977)

  • P. Leyland, John Roberts, The cohomology of nets over Minkowski space (EUCLID)

Here the idea was put forward that local nets of observables should carry a notion of cohomology – or rather of nonabelian cohomology – with coefficients in some kind of ∞-category. Motivated by this John Roberts was one of the first to consider strict ∞-categories. He conjectured that these are characterized by their ∞-nerves being complicial sets. This led Ross Street to develop the notion of orientals and eventually to prove this conjecture. An account of this development is on pages 9-10 of

  • Ross Street, An Australian conspectus of higher category theory (pdf)

More comments on the role of cohomology in AQFT are in

  • John Roberts, A survey of local cohomology Mathematical Problems in Theoretical Physics Lecture Notes in Physics, (1978) Volume 80/1978

  • John Roberts, Net cohomology and its applications to field theory, Quantum fields-algebras, processes (Proc. Sympos., Univ. Bielefeld, Bielefeld, 1978), pp. 239-268, Springer, Vienna (1980).

  • John Roberts, The Search for Quantum Differential Geometry Mathematical Problems in Theoretical Physics, Lecture Notes in Physics, (1982) Volume 153/1982, 374-379

  • John Roberts, The cohomology and homology of quantum field theory at Quantum fields and quantum space time (Cargèse, 1996), 357-368, NATO Adv. Sci. Inst. Ser. B Phys., 364, Plenum, New York, (1997)

The description of DHR superselection theory in terms of net cohomology was given in

Its generalization to general spacetimes (curved and with nontrivial topology) is discussed in

The trivial Sectors of the Massless scalar free field in 1 + 3 dimensions was discussed in

  • Buchholz, Doplicher, Longo, Roberts (1992)

  • Fabio Ciolli, Massless scalar free Field in 1+11+1 dimensions, II: Net Cohomology and Completeness of Superselection Sectors (arXiv:0811.4673)


Last revised on October 26, 2011 at 00:44:09. See the history of this page for a list of all contributions to it.