  The virial theorem, and the equipartition theorem in the case of quadratic
degrees of freedom, are handy constraints on the statistics of equilibrium
systems. Their violation is instrumental in determining how far from
equilibrium a driven system might be. We extend the virial theorem to
nonequilibrium conditions for Langevin dynamics with nonlinear friction and
multiplicative noise. In particular, we generalize the equipartition theorem
for confined laser-cooled atoms in the semi-classical regime. The resulting
relation between the lowest moments of the atom position and velocity allows to
measure in experiments how dissipative the cooling mechanism is. Moreover, its
violation can reveal the departure from a strictly harmonic confinement or from
the semi-classical regime.
