Superfluid Mutual-friction Coefficients from Vortex Dynamics in the Two-dimensional Galerkin-truncated Gross-Pitaevskii Equation

We present algorithms for the ab-initio determination of the temperature ($T$) dependence of the mutual-friction coefficients $\alpha$ and ${\alpha }^{\mathrm{\prime }}$ and the normal-fluid density ${\rho }_{\mathrm{n}}$ in the two-dimensional (2D) Galerkin-truncated Gross-Pitaevskii system. Our algorithms enable us to determine $\alpha (T)$, even though fluctuations in 2D are considerably larger than they are in 3D. We also examine the implications of our measurements of ${\alpha }^{\mathrm{\prime }}(T)$ for the Iordanskii force, whose existence is often questioned.