Correlation function and generalized master equation of arbitrary age
  We study a two-state statistical process with a non-Poisson distribution of sojourn times. In accordance with earlier work, we find that this process is characterized by aging and we study three different ways to define the correlation function of arbitrary age of the corresponding dichotomous fluctuation based respectively on the Generalized Master Equation formalism, on a Liouville-like approach and on a trajectory perspective. 
Paolo Allegrini, Gerardo Aquino, Paolo Grigolini, Luigi Palatella,   Angelo Rosa and Bruce J. West