On Infravacua and Superselection Theory
  
  
  
      
    Walter Kunhardt
  
  
  
  
  
  
                
    
  April 30, 1997  
  
    In the DHR theory of superselection sectors, one usually considers states
which are local excitations of some vacuum state. Here, we extend this analysis
to local excitations of a class of "infravacuum" states appearing in models
with massless particles. We show that the corresponding superselection
structure, the statistics of superselection sectors and the energy-momentum
spectrum are the same as with respect to the vacuum state. (The latter result
is obtained with a novel method of expressing the shape of the spectrum in
terms of properties of local charge transfer cocycles.) These findings provide
evidence to the effect that infravacua are a natural starting point for the
analysis of the superselection structure in theories with long-range forces.
  
  
    
  
  Keywords: 
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