No abstract

We present the results of a one-loop calculation of the effect of a van der Waals type interaction potential ∼ |x| −d−σ on the critical Casimir force and specific heat of confined 4 He near the superfluid transition. We consider a 4 He film of thickness L. In the region L ξ (correlation length) we find that the van der Waals interaction causes a leading non-universal non-scaling contribution of O(ξ 2 L −d−σ ) to the critical temperature dependence of the Casimir force above T λ that dominates the universal scaling contribution ∼ e −L/ξ predicted by earlier theories. For the specific heat we find subleading non-scaling contributions of O(L −1 ) and O(L −d−σ ).