  In a fluid out of equilibrium, the fluctuation dissipation theorem (FDT) is
usually violated. Using molecular dynamics simulations, we study in detail the
relationship between correlation and response functions in a fluid driven into
a stationary non-equilibrium state. Both the high temperature fluid state and
the low temperature glassy state are investigated. In the glassy state, the
violation of the FDT is quantitatively identical to the one observed previously
in an aging system in the absence of external drive. In the fluid state,
violations of the FDT appear only when the fluid is driven beyond the linear
response regime, and are then similar to those observed in the glassy state.
These results are consistent with the picture obtained earlier from theoretical
studies of driven mean-field disordered models, confirming the similarity
between these models and real glasses.
