Manifolds in random media: Beyond the variational approximation

In this paper we give a closed form expression for the $1/d$ corrections to the self-energy characterizing the correction function of a manifold in random media. This amounts to the first correction beyond the variational approximation. At this time we were able to evaluate this corrections in the high temperature ``phase'' of the notorious toy-model describing a classical particle subject to the influence of both a harmonic potential and a random potential. Although in this phase the correct solution is replica symmetric the calculation is non-trivial. The outcome is compared with previous analytical and numerical results. The corrections diverge at the ``transition'' temperature.