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.

Acknowledgements

The authors would like to thank the referees for their careful reading of the manuscript, which helped both improving the presentation and removing typos and some errors.

Citation

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Søren Asmussen. 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

Information

Received: 1 April 2022; Published: February 2024
First available in Project Euclid: 8 November 2023

MathSciNet: MR4665582
zbMATH: 07788888
Digital Object Identifier: 10.3150/23-BEJ1601

Keywords: Boltzmann law , Conditioned Brownian motion , empirical c.d.f. , exponential tilting , Functional limit theorem , Gibbs conditioning , saddlepoint approximation , total variation distance

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Vol.30 • No. 1 • February 2024
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