A simple proof of heavy tail estimates for affine type Lipschitz recursions

We study the affine recursion $X_n = A_nX_{n-1}+B_n$ where $(A_n,B_n)\in {\mathbb R}^+ \times {\mathbb R}$ is an i.i.d. sequence and recursions $X_n = Φ_n(X_{n-1})$ defined by Lipschitz transformations such that $Φ(x)\geq Ax+B$. It is known that under appropriate hypotheses the stationary solution $X$ has regularly varying tail, i.e. $\lim_{t\to\infty} t^α {\mathbb P}[X>t] = C.$ However positivity of $C$ in general is either unknown or requires some additional involved arguments. In this paper we give a simple proof that $C>0$. This applies, in particular, to the case when Kesten-Goldie assumptions are satisfied.

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