ModelFin two-loop order and the thermal conductivity near the superfluid transition ofHe4

Abstract

A nonlinear renormalization-group (RG) analysis of the thermal conductivity data near the $\ensuremath{\lambda}$ line of $^{4}\mathrm{He}$ is performed on the basis of the corrected dynamic RG flow equations of model $F$ in two-loop order. Our analysis eliminates recent uncertainties in the regime $(T\ensuremath{-}{T}_{\ensuremath{\lambda}})∕{T}_{\ensuremath{\lambda}}\ensuremath{\lesssim}{10}^{\ensuremath{-}6}$, which is most sensitive to the effect of the weak-scaling fixed point. This effect is found to be stronger than described previously. We also improve the Borel summation of the amplitude of the specific heat.