  We consider an impurity in a sea of zero-temperature fermions uniformly
distributed throughout the space. The impurity scatters on fermions. On
average, the momentum of impurity decreases with time as $t^{-1/(d+1)}$ in $d$
dimensions, and the momentum distribution acquires a scaling form in the long
time limit. We solve the Lorentz-Boltzmann equation for the scaled momentum
distribution of the impurity in three dimensions. The solution is a combination
of confluent hypergeometric functions. In two spatial dimensions, the
Lorentz-Boltzmann equation is analytically intractable, so we merely extract a
few exact predictions about asymptotic behaviors when the scaled momentum of
the impurity is small or large.
