  A new powerful method to test the stability of the replica symmetric spin
glass phase is proposed by introducing a replicon generator function g(v).
Exact symmetry arguments are used to prove that its extremum is proportional to
the inverse spin glass susceptibility. By the idea of independent droplet
excitations a scaling form for g(v) can be derived, whereas it can be exactly
computed in the mean field Sherrington-Kirkpatrick model. It is shown by a
first order perturbative treatment that the replica symmetric phase is unstable
down to dimensions d<6, and the mean field scaling function proves to be very
robust. Although replica symmetry breaking is escalating for decreasing
dimensionality, a mechanism caused by the infrared divergent replicon
propagator may destroy the mean field picture at some low enough dimension.
