Schwartz Linear operators in distribution spaces
  In this paper we define the Schwartz linear operators among spaces of tempered distributions. These operators are the analogous of linear continuous operators among separable Hilbert spaces, but in the case of spaces endowed with Schwartz bases having a continuous index set. The Schwartz linear operators enjoy properties very similar to those enjoyed by linear operators in the finite dimensional case. The Schwartz operators are one possible rigorous mathematical model for the operators and observables used in Quantum Mechanics. 
David Carf\'i
math.FA quant-ph