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Asymptotics for the expected maximum of random walks and Lévy flights with a constant drift

Abstract : In this paper, we study the large $n$ asymptotics of the expected maximum of an $n$-step random walk/L\'evy flight (characterized by a L\'evy index $1<\mu\leq 2$) on a line, in the presence of a constant drift $c$. For $0<\mu\leq 1$, the expected maximum is infinite, even for finite values of $n$. For $1<\mu\leq 2$, we obtain all the non-vanishing terms in the asymptotic expansion of the expected maximum for large $n$. For $c<0$ and $\mu =2$, the expected maximum approaches a non-trivial constant as $n$ gets large, while for $1<\mu < 2$, it grows as a power law $\sim n^{2-\mu}$. For $c>0$, the asymptotic expansion of the expected maximum is simply related to the one for $c<0$ by adding to the latter the linear drift term $cn$, making the leading term grow linearly for large $n$, as expected. Finally, we derive a scaling form interpolating smoothly between the cases $c=0$ and $c\ne 0$. These results are borne out by numerical simulations in excellent agreement with our analytical predictions.
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Contributor : Claudine Le Vaou <>
Submitted on : Monday, October 29, 2018 - 4:34:14 PM
Last modification on : Wednesday, September 16, 2020 - 4:05:54 PM

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Philippe Mounaix, Satya N. Majumdar, Gregory Schehr. Asymptotics for the expected maximum of random walks and Lévy flights with a constant drift. Journal of Statistical Mechanics: Theory and Experiment, IOP Publishing, 2018, 2018 (8), ⟨10.1088/1742-5468/aad364⟩. ⟨hal-01907941⟩

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