Replica Plefka expansion of Ising systems

The replica extension theory has been developed for the purpose of investigating spin glass systems in the replica symmetry breaking phase. The replica extension theory is a replica theory for a specific sample and has the scheme of the one-step replica symmetry breaking ansatz. In this paper, using the Plefka expansion, we propose the perturbative expansion of Gibbs free energies of Ising systems with the replica extension theory, and we derive the explicit form of the second-and third-order approximations. Our Plefka expansion systematically provides perturbative approximations taking the one-step replica symmetry breaking into account. In some numerical experiments, we show that our perturbative approximations are quantitatively superior to conventional perturbative approximations that do not take the one-step replica symmetry breaking into account in the spin glass phase.