Vortex-ring model of the superfluid λ transition

An initial model of the superfluid λ transition is constructed with use of vortex-ring excitations, as originally suggested by Onsager and Feynman. A real-space renormalization technique generates a screened vortex energy and core size, and gives rise to a transition where rings of infinite diameter are excited as the superfluid density approaches zero at T_c. Although the model satisfies the Josephson hyperscaling relation, it is not yet a complete theory: The superfluid density exponent is ν=0.53, and does not match the known value ν=0.67.