New superfields for N supersymmetry with central charges

The authors show that a judicious choice of nonlinear realisation of centrally extended N supersymmetry permits the construction of chiral-like superfields with a 2 N-dimensional a-number parameter, at the expense of an external 'superspin' index which labels multiplets of several irreducible representations of the Lorentz group. The generalised superfields considered have 4sup(N+[N/2]) component fields altogether, as opposed to the 16sup(N) expected conventionally. The N = 2 case is examined in detail, and the decomposition of arbitrary spin superfields into irreducible parts is given. The connection with other N = 2 superfield analyses is pointed out, and the structure of 'spin-reducing' representations with p2+|Z|2=0 is exhibited. (author)