Abstract
We show that, above the critical temperature, if the dimension
D
of a given Ising spin glass model is sufficiently high, its free energy can be effectively
expressed through the free energy of a related Ising model. When, in a broad sense,
, in the paramagnetic phase and on its boundary the mapping is exact. In this limit the
method provides a general and simple rule for obtaining exactly the upper phase
boundaries. We even provide simple effective rules for finding crossover surfaces
and correlation functions. We apply the mapping to several spin glass models.