REPLICA SYMMETRY-BREAKING AND THE RENORMALIZATION-GROUP THEORY OF THEWEAKLY DISORDERED FERROMAGNET

We study the critical properties of the weakly disordered p-component ferromagnet in terms of the renormalization group (Re) theory generali zed to take into account the replica symmetry breaking (RSB) effects c oming from the multiple local minima solutions of the mean-field equat ions. Recently it has been shown that for p < 4 the traditional RG Bow s at dimensions D = 4 - epsilon, which are usually considered as descr ibing the disorder-induced universal critical behaviour, are unstable with respect to the RSB potentials as found in spin glasses, and a new type of stable one-step RSB fixed point has been discovered [1]. Here it is demonstrated that for a general type of the Parisi RSB structur es there exist no stable fixed points, and the RG flows lead to the st rong-coupling regime at the finite scale R similar to exp(1/u), where u is the small parameter describing the disorder. The physical conseq uences of the obtained RG solutions are discussed. In particular, we a rgue that discovered RSB strong-coupling phenomena indicate the onset of a new spin-glass-type critical behaviour in the temperature interva l tau < tau similar to exp(-1/u) near Tr. The possible relevance of t he considered RSB effects for the Griffith phase is also discussed.