Comment on ‘fluctuation-dominated phase ordering at a mixed order transition’

Abstract

Abstract Renewal processes generated by a power-law distribution of intervals with tail index less than unity are genuinely non-stationary. This issue is illustrated by a critical review of the recent paper by Barma, Majumdar and Mukamel (2019 J. Phys. A 52 254001), devoted to the investigation of the properties of a specific one-dimensional equilibrium spin system with long-range interactions. We explain why discarding the non-stationarity of the process underlying the model leads to an incorrect expression of the critical spin–spin correlation function, even when the system, subjected to periodic boundary conditions, is translation invariant.