An introduction to generalised functions in periodic quantum theory
  A proof that minimum uncertainty states of the simplest periodic quantum system exist in a state space that is represented by a Colombeau algebra of generalised functions but not in Hilbert space or in the space of Schwartz distributions is given. There are two significant generalisations of Hilbert space that lead to the special Colombeau algebra. The first step is to a vector space of Schwartz distributions that contains the eigenstates of operators with continuous spectra, the second is to a Colombeau algebra that provides a solution for a differential equation with non-constant coefficients.   From the perspective of Colombeau algebra a rigged Hilbert space of Schwartz distributions can be understood as a representation of the linear component of the algebra. The utility of this representation is illustrated by a proof that generalised eigen-decompositions exist for linear operators with periodic continuous spectra. 
Ian G Fuss, Alexei Filinkov
math-ph math.MP quant-ph