arXiv2021
We prove a Berry-Esseen theorem and Edgeworth expansions for partial sums of the form $S_N=\sum_{n=1}^{N}f_n(X_n,X_{n+1})$, where $\{X_n\}$ is a uniformly elliptic inhomogeneous Markov chain and $\{f_n\}$ is a sequence of uniformly bounded functions. The Berry-Esseen theorem holds without additional assumptions, while expansions of order $1$ hold when $\{f_n\}$ is irreducible, which is an optimal condition. For higher order expansions, we then focus on two situations. The first is when the essential supremum of $f_n$ is of order $O(n^{-\be})$ for some $\be\in(0,1/2)$. In this case it turns out that expansions of any order $r<\frac1{1-2\be}$ hold, and this condition is optimal. The second case is uniformly elliptic chains on a compact Riemannian manifold. When $f_n$ are uniformly Lipschitz continuous we show that $S_N$ admits expansions of all orders. When $f_n$ are uniformly Hölder continuous with some exponent $\al\in(0,1)$, we show that $S_N$ admits expansions of all orders $r<\frac{1+\al}{1-\al}$. For Hölder continues functions with $\al<1$ our results are new also for uniformly elliptic homogeneous Markov chains and a single functional $f=f_n$. In fact, we show that the condition $r<\frac{1+\al}{1-\al}$ is optimal even in the homogeneous case.