Concentration dependence of theHe3quasiparticle interaction in dilute solutions ofHe3in superfluidHe4

On the basis of an analysis of transport-coefficient data for dilute solutions of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, Kuenhold and Ebner found evidence that the interaction between ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ quasiparticles depends on the concentration of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. We have estimated the size of concentration-dependent contributions to the effective interaction, assuming the zero-concentration form of the interaction to be known. These contributions vary as $x^{\frac{1}{3}}$, where $x$ is the concentration of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ atoms, and are appreciable even for concentrations of a few percent. We find that the theoretical estimates of the spin-diffusion coefficient and thermal conductivity in the low-temperature limit are generally reduced by the concentration-dependent contribution to the interaction. For a simple form of the zero-concentration interaction the experimental data on these transport coefficients for 1.3- and 5-at.% solutions can be fitted significantly better if the concentration-dependent terms are included than if they are neglected.