A test for the existence of a fractional root in a non-stationary time series

In this work, we present a modification of the hypothesis testing procedure for the existence of long memory in the stationary and invertible ARFIMA(p,d,q) process proposed by Castaño, Gómez and Gallón (2008). This modification allows assessing the existence of a fractional root in a non-stationary time series when the short-term ARMA component is undetermined or unknown, especially in ARFIMA(p,d,q) processes. We validate, via Monte Carlo simulations, the analytical results and demonstrate the good performance of the proposed test in terms of both power and size, in comparison to other well-known tests in the literature.