Some remarks on Gordin-Lif\v{s}ic's condition for martingale approximations

Abstract

In this note, we study a condition introduced by Gordin and Lif{\v s}ic in 1981 to establish the Central Limit Theorem for additive functionals of stationary Markov chains with normal transition operator. In the more general setting of strictly stationary sequences satisfying the Gordin-Lif{\v s}ic condition, we give sufficient (and sometimes also necessary) conditions for partial sums to be approximated in L2 by a martingale with stationary increments. Various types of L2 approximations are described, leading to different versions of the central limit theorem (annealed, quenched, functional form...). The optimality of the conditions is discussed, and an application to the class of semi-linear processes is presented.