A systematic expansion for random Ising models

An approximation scheme for random Ising models on a square lattice is derived for the case of a symmetric probability distribution of the couplings. The calculation is explicitly performed for the binary distribution. It is suggested that the quenched free energy is an analytic function of the temperature down toT=0, and that a spin glass phase as a phase in the usual sense does not exist. Rigorous nontrivial bounds for the ground state energy and the ground state entropy are also obtained.Work performed within the research program of the Sonderforschungsbereich 125 Aachen-Jülich-Köln