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 ... has infinite energy, it labels superselection sectors where the difference in energy between two states is finite ... there is an additional infinity of superselection sectors, each labelled by a different value of the unbroken SO(2) charge ...