Classification of Subsystems for Local Nets with Trivial Superselection   Structure
  Let F be a local net of von Neumann algebras in four spacetime dimensions satisfying certain natural structural assumptions. We prove that if F has trivial superselection structure then every covariant, Haag-dual subsystem B is the fixed point net under a compact group action on one component in a suitable tensor product decomposition of F. Then we discuss some application of our result, including free field models and certain theories with at most countably many sectors. 
Sebastiano Carpi (1), Roberto Conti (2) ((1) University of Rome 1, (2)   University of Rome 2)