  In fusion reactions, the Coulomb barrier selects particles from the
high-momentum part of the distribution. Therefore, small variations of the
high-momentum tail of the velocity distribution can produce strong effects on
fusion rates. In plasmas several potential mechanisms exist that can produce
deviations from the standard Maxwell-Boltzmann distribution. Quantum broadening
of the energy-momentum dispersion relation of the plasma quasi-particles
modifies the high-momentum tail and could explain the fusion-rate enhancement
observed in low-energy nuclear reaction experiments.
