On the geometric ergodicity of nonlinear multivariate time series
  In this paper we consider multivariate time series obtained as solution to multidimensional nonlinear stochastic difference equations whose coefficients are allowed to be locally degenerate and to present discontinuities. We provide simple and easy to check sufficient conditions for the irreducibility, T-chain regularity and geometric ergodicity of these processes and apply the results to the BEKK-ARCH(1) models with a nonlinear autoregressive term. 
Marco Ferrante and Giovanni Fonseca
math.PR