by Giorgio Parisi and Nicolas Sourlas who "observed that the most infrared divergent diagrams are those with the maximum number of random source insertions, and, if the other diagrams are neglected, one is left with a diagrammatic expansion for a classical field theory in the presence of random sources... Parisi and Sourlas explained this dimensional reduction by a hidden supersymmetry." See also Compactification (physics) Kaluza–Klein theory String theory#Extra dimensions Supergravity Quantum gravity Supersymmetric theory of stochastic dynamics References String theory Quantum field theory Supersymmetry