  We develop a theory of energy relaxation and thermalization of hot carriers
in real quantum wires. Our theory is based on a controlled perturbative
approach for large excitation energies and emphasizes the important roles of
the electron spin and finite temperature. Unlike in higher dimensions,
relaxation in one-dimensional electron liquids requires three-body collisions
and is much faster for particles than holes which relax at nonzero temperatures
only. Moreover, co-moving carriers thermalize more rapidly than
counterpropagating carriers. Our results are quantitatively consistent with a
recent experiment.
