Fluctuation-dissipation relations and energy landscape in an out-of-equilibrium strong-glass-forming liquid.

We study the out-of-equilibrium dynamics following a temperature jump in a model for silica, a strong liquid, and compare it with the well known case of fragile liquids. We calculate the fluctuation-dissipation relation, from which it is possible to estimate an effective temperature T(eff) associated with the slow out-of-equilibrium structural degrees of freedom. We find the striking and unexplained result that, different from the fragile liquid cases, T(eff) is smaller than the bath temperature.