Real-space renormalization for the finite temperature statics and dynamics of the Dyson Long-Ranged Ferromagnetic and Spin-Glass models

Abstract: The finite temperature dynamics of the Dyson hierarchical classical spins models is studied via real-space renormalization rules concerning the couplings and the relaxation times. For the ferromagnetic model involving Long-Ranged coupling $J(r) \propto r^{-1-\sigma}$ in the region $1/2<\sigma<1$ where there exists a non-mean-field-like thermal Ferromagnetic-Paramagnetic transition, the RG flows are explicitly solved: the characteristic relaxation time $\tau(L)$ follows the critical power-law $\tau(L)\propto L^{z_c(\sigma)} $ at the phase transition and the activated law $\ln \tau(L)\propto L^{\psi} $ with $\psi=1-\sigma$ in the ferromagnetic phase. For the Spin-Glass model involving random Long-Ranged couplings of variance $\overline{J^2(r)} \propto r^{-2\sigma}$ in the region $2/3<\sigma<1$ where there exists a non-mean-field-like thermal SpinGlass-Paramagnetic transition, the coupled RG flows of the couplings and of the relaxation times are studied numerically : the relaxation time $\tau(L)$ follows some power-law $\tau(L)\propto L^{z_c(\sigma)} $ at criticality and the activated law $\ln \tau(L)\propto L^{\psi} $ in the Spin-Glass phase with the dynamical exponent $\psi=1-\sigma=\theta$ coinciding with the droplet exponent governing the flow of the couplings $J(L) \propto L^{\theta} $.