Fixed points and their stability in the functional renormalization group of random field models

Abstract: We consider the zero-temperature fixed points controlling the critical behavior of the $d$-dimensional random-field Ising, and more generally $O(N)$, models. We clarify the nature of these fixed points and their stability in the region of the $(N,d)$ plane where one passes from a critical behavior satisfying the $d\rightarrow d-2$ dimensional reduction to one where it breaks down due to the appearance of strong enough nonanalyticities in the functional dependence of the cumulants of the renormalized disorder. We unveil an intricate and unusual behavior.