Fractional Quantum Field Theory, Path Integral, and Stochastic   Differential Equation for Strongly Interacting Many-Particle Systems
  While free and weakly interacting particles are well described by a a second-quantized nonlinear Schr\"odinger field, or relativistic versions of it, the fields of strongly interacting particles are governed by effective actions, whose quadratic terms are extremized by fractional wave equations. Their particle orbits perform universal L\'evy walks rather than Gaussian random walks with perturbations. 
H. Kleinert
quant-ph