Hellmut Baumgaertel, Hendrik Grundling
Superselection and Constraints
(144K, LATEX)

ABSTRACT.  For systems which contain both 
superselection structure and constraints, we study compatibility 
between constraining and superselection. Specifically, we start with a 
generalisation of Doplicher-Roberts superselection theory 
to the case of nontrivial centre, and a set of Dirac quantum constraints 
and find conditions under which the superselection structures will 
survive constraining in some form. This involves an analysis 
of the restriction and factorisation of superselection structures. 
We develop an example for this theory, modelled on interacting QED.