  We show that the single-particle and transport relaxation rates in
ferromagnetic metals, which determine the thermal and electrical conductivity,
respectively, at asymptotically low temperature do not obey a power law as
previously thought, but rather show an exponential temperature dependence. The
reason is the splitting of the conduction band that inevitably results from a
nonzero magnetization. At higher temperatures there is a sizable temperature
window where the transport rate shows a T^2 temperature dependence, in accord
with prior results. This window is separated from the asymptotic regime by a
temperature scale that is estimated to range from tens of mK to tens of K for
typical ferromagnets. We motivate and derive a very general effective theory
for metallic magnets that we then use to derive these results. Comparisons with
existing experiments are discussed, and predictions for future experiments at
low temperatures are made.
