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The area of an exponential random walk and partial sums of uniform order statistics
Authors:V V Vysotsky
Institution:(1) St.Petersburg State University, St.Petersburg, Russia
Abstract:Let Si be a random walk with standard exponential increments. The sum ∑ i=1 k Si is called the k-step area of the walk. The random variable 
$$\mathop {\inf }\limits_{k \geqslant 1} \tfrac{2}{{k(k + 1)}}$$
i=1 k Si plays an important role in the study of the so-called one-dimensional sticky particles model. We find the distribution of this variable and prove that

$$\mathbb{P}\left\{ {\mathop {\inf }\limits_{k \geqslant 1} \tfrac{2}{{k(k + 1)}}\sum\limits_{i = 1}^k {S_i }  \geqslant t} \right\} = \mathbb{P}\left\{ {\mathop {\inf }\limits_{k \geqslant 1} \sum\limits_{i = 1}^k {(S_i  - it)}  \geqslant 0} \right\} = \sqrt {1 - t} e^{ - t/2} $$
for 0 ≤ t ≤ 1. We also show that

$$\mathop {\lim }\limits_{n \to \infty } \mathbb{P}\left\{ {\mathop {\min }\limits_{1 \leqslant k \leqslant n} \tfrac{{2n}}{{k(k + 1)}}\sum\limits_{i = 1}^k {U_{i,n} }  \geqslant t} \right\} = \sqrt {1 - t} e^{ - t/2} $$
, where the Ui,n are order statistics of n i.i.d. random variables uniformly distributed on 0, 1]. Bibliography: 6 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 341, 2007, pp. 48–67.
Keywords:
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