Title: "Liquid Helium and QCD: Feynman’s Last Problem 30+ Years Later"

Abstract:  In 1954, Feynman gave a beautiful analysis of superfluid Helium using general properties of wave functions and of the space of particle configurations. In the 1970s, with the emergence of QCD, the question of quark confinement and the generation of a mass gap was recognized as an important question about the nonperturbative behavior of nonabelian gauge theories. QCD in two spatial dimensions would provide the simplest case of  a nontrivial gauge theory which could exhibit confinement and mass gap. In 1981, Feynman tried to use a set of arguments similar to what he had developed for superfluidity to argue for the existence of a mass gap for these theories. Did he succeed? If so, to what extent?