  We develop an effective field theory (EFT) framework for superfluid ${}^4$He
to model the interactions among quasiparticles, helium atoms and probe
particles. Our effective field theory approach brings together symmetry
arguments and power-counting and matches to classical fluid dynamics. We then
present the decay and scattering rates for the relevant processes involving
quasiparticles and helium atoms. The presented EFT framework and results can be
used to understand the dynamics of thermalization in the superfluid, and can be
further applied to sub-GeV dark matter direct detection with superfluid
${}^4$He.
