Cluster Estimates and Analytic Wavefunctions
  The Tomita-Takesaki modular theory is used to establish a cluster estimate extending and modifying that of Thomas and Wichmann, so as to extend it to regions within which the relevant observables are not necessarily spacelike separated. This sort of estimate is then applied to the case of a massive free field, to show that wavefunctions localized in a certain sense are analytic functions of momentum. 
D. R. Davidson