Using a coupling for the weighted sum of independent random variables and the explicit expression of the transition semigroup of Ornstein-Uhlenbeck processes driven by compound Poisson processes, we establish the existence of a successful coupling and the Liouville theorem for general Ornstein-Uhlenbeck processes. Then we present the explicit coupling property of Ornstein-Uhlenbeck processes directly from the behaviour of the corresponding symbol or characteristic exponent. This approach allows us to derive gradient estimates for Ornstein-Uhlenbeck processes via the symbol.
Main resultsLet (X x t ) t≥0 be an n-dimensional Ornstein-Uhlenbeck process, which is defined as the unique strong solution of the following stochastic differential equation(1.1)Here A is a real n × n matrix, B is a real n × d matrix and Z t is a Lévy process in R d ; note that we allow Z t to take values in a proper subspace of R d . It is well known thatThe characteristic exponent or symbol of Z t , defined byenjoys the following Lévy-Khintchine representation:where Q = (q j,k ) d j,k=1 is a positive semi-definite matrix, b ∈ R d is the drift vector and ν is the Lévy measure, i.e. a σ -finite measure on R d \{0} such that the integral z =0 (1 ∧ |z| 2 ) ν(dz) < ∞. For every ε > 0, define ν ε on R d as follows: (2000): 60J25, 60J75
Mathematics Subject Classification