Radiative corrections to the decay rate of charged fermions caused by the
presence of a thermal bath of photons are calculated in the limit when
temperatures are below the masses of all charged particles involved. The
cancellation of finite-temperature infrared divergences in the decay rate is
described in detail. Temperature-dependent radiative corrections to a two-body
decay of a hypothetical charged fermion and to electroweak decays of a muon are
given. We touch upon possible implications of these results for charged
particles in the early Universe.Comment: 18 pages, 6 figures. v2: typos corrected, bibliography revised,
content matches published versio
