February 2024 Refined behaviour of a conditioned random walk in the large deviations regime
Søren Asmussen, Peter W. Glynn
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Bernoulli 30(1): 371-387 (February 2024). DOI: 10.3150/23-BEJ1601
Abstract

Conditioned limit theorems as n are given for the increments X1,,Xn of a random walk Sn=X1++Xn, subject to the conditionings Snnb or Sn=nb with b>EX. The probabilities of these conditioning events are given by saddlepoint approximations, corresponding to the exponential tilting fθ(x)= eθxψ(θ)f(x) of the increment density f(x), with θ satisfying b=EθX=ψ(θ) where ψ(θ)=logEeθX. It has been noted in various formulations that conditionally, the increment density somehow is close to fθ(x). Sharp versions of such statements are given, including correction terms for segments (X1,,Xk) with k fixed. Similar correction terms are given for the mean and variance of Fˆn(x)Fθ(x) where Fˆn is the empirical c.d.f. of X1,,Xn. Also a result on the total variation distance for segments with knc(0,1) is derived. Further functional limit theorems for (Fˆk(x),Sk)kn are given, involving a bivariate conditioned Brownian limit.

Søren Asmussen and Peter W. Glynn "Refined behaviour of a conditioned random walk in the large deviations regime," Bernoulli 30(1), 371-387, (February 2024). https://doi.org/10.3150/23-BEJ1601
Received: 1 April 2022; Published: February 2024
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Vol.30 • No. 1 • February 2024
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