Universality of the thermodynamic Casimir effect

TL;DR

This paper demonstrates that the thermodynamic Casimir force is universal in systems with short-ranged interactions when properly accounting for momentum cutoff effects, correcting previous claims of nonuniversality.

Contribution

It clarifies the universal nature of the Casimir force by analyzing the effects of a sharp momentum cutoff and contrasting lattice and continuum models.

Findings

No leading nonuniversal term in short-ranged systems with proper cutoff treatment

Lattice and continuum models agree on Casimir force results

Finite-size effects in long-ranged interactions follow power laws

Abstract

Recently a nonuniversal character of the leading spatial behavior of the thermodynamic Casimir force has been reported [X. S. Chen and V. Dohm, Phys. Rev. E {\bf 66}, 016102 (2002)]. We reconsider the arguments leading to this observation and show that there is no such leading nonuniversal term in systems with short-ranged interactions if one treats properly the effects generated by a sharp momentum cutoff in the Fourier transform of the interaction potential. We also conclude that lattice and continuum models then produce results in mutual agreement independent of the cutoff scheme, contrary to the aforementioned report. All results are consistent with the {\em universal} character of the Casimir force in systems with short-ranged interactions. The effects due to dispersion forces are discussed for systems with periodic or realistic boundary conditions. In contrast to systems with short-ranged interactions, for $L/\xi \gg 1$ one observes leading finite-size contributions governed by power laws in $L$ due to the subleading long-ranged character of the interaction, where $L$ is the finite system size and $\xi$ is the correlation length.