Superselection Sectors

Some articles on superselection sectors:

Mathematical Formulation Of Quantum Mechanics - Mathematical Structure of Quantum Mechanics - Postulates of Quantum Mechanics
... Superselection sectors ... between states and rays needs to be refined somewhat to take into account so-called superselection sectors ... States in different superselection sectors cannot influence each other, and the relative phases between them are unobservable ...
Superselection Sectors - Continuous Symmetries
... In the disordered phase, the superselection sectors are described by the representation of SO(3) under which a given configuration transforms globally ... so that the field everywhere points in the same direction, there is an additional infinity of superselection sectors, each labelled by a different value of the unbroken SO(2) charge ... state, there is a mass gap for the superselection sectors labeled by a nonzero integer, because the topological solitons are massive even infinitely massive ...