  We study the effects of thermal, hard particles on nucleation rates in
high-temperature quantum field theories (QFTs). The hard particles, which form
the heat bath for nucleating fields, can be regarded as the most qualitatively
distinct aspect of high-temperature QFTs in comparison with Langer's classical
nucleation theory: They have their own dynamics and interactions with the
nucleating fields, and consequently they do not obey a purely equilibrium
distribution during nucleation. We focus on the situation where the hard
particles are correctly described by a Vlasov equation, and show that the hard
particles can be included into Langer's framework, with only the dynamical part
of the nucleation rate changing. The statistical part retains its form and is
in accordance with the effective field theory approach to thermal nucleation.
It is also shown that the dominant damping from a light bosonic quantum field
comes from the corresponding long-wavelength classical field instead of the
corresponding bosonic hard particles.
