Pointwise estimates for first passage times of perpetuity sequences

Abstract

We consider first passage times $τ_u = \inf\{n:\; Y_n>u\}$ for the perpetuity sequence $$ Y_n = B_1 + A_1 B_2 + \cdots + (A_1\ldots A_{n-1})B_n, $$ where $(A_n,B_n)$ are i.i.d. random variables with values in ${\mathbb R} ^+\times {\mathbb R}$. Recently, a number of limit theorems related to $τ_u$ were proved including the law of large numbers, the central limit theorem and large deviations theorems. We obtain a precise asymptotics of the sequence ${\mathbb P}[τ_u = \log u/ρ]$, $ρ>0$, $u\to \infty $ which considerably improves the previous results. There, probabilities ${\mathbb P}[τ_u \in I_u]$ were identified, for some large intervals $I_u$ around $k_u$, with lengths growing at least as $\log\log u$. Remarkable analogies and differences to random walks are discussed.