Longitudinal and transverse forces on a vortex in superfluid He-4

We examine the transverse and longitudinal components of the drag force upo n a straight vortex line due to the scattering of liquid He-4 excitations. For this purpose, we consider a recently proposed Hamiltonian that describe s the dissipative motion of a vortex, giving an explicit expression for the vortex-quasiparticle interaction. The dissipative coefficients involved ar e obtained in terms of the reservoir correlation function. Most of our expl icit calculations are concerned with the range of temperatures below 0.4 K, for which the reservoir is composed of phonon quasiparticle excitations. W e also discuss some important implications for the determination of possibl e scattering processes leading to dissipation, on the basis of the values o f the vortex mass found in the literature.