dorsal/arxiv
View SchemaUpper moderate deviation probabilities for the maximum of a branching random walk
| Authors | Louis Chataignier, Lianghui Luo |
|---|---|
| Categories | |
| ArXiv ID | 2601.08766vv1 |
| URL | https://arxiv.org/abs/2601.08766 |
| License | http://creativecommons.org/licenses/by/4.0/ |
Abstract
Consider $M_n$ the maximal position at generation $n$ of a supercritical branching random walk. A\"id\'ekon (2013) obtained and described the convergence in law, as time $n$ goes to infinity, of $M_n-m_n$, where $m_n$ is an explicit function. Equivalently, he identified the limit of $\mathbb{P}(M_n > m_n + x)$, for any $x \in \mathbb{R}$. More recently, Luo (2025) gave an asymptotic equivalent for the upper large deviation probability, that is $\mathbb{P}(M_n > m_n + xn)$, for $x > 0$. In this work, we study an intermediate regime, called upper moderate deviation. We obtain, under close-to-optimal integrability conditions, an asymptotic equivalent for $\mathbb{P}(M_n > m_n + x_n)$, where $x_n$ is such that $x_n \to \infty$ and $x_n = O(\sqrt{n})$. Our proof is based on a strategy due to Bramson, Ding, and Zeitouni (2016). As a byproduct, we obtain information about the typical behavior of particles contributing to such deviations. Finally, we apply our main result to show the convergence in law of the centered maximum of a two-speed branching random walk in the mean regime and describe its limit.
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"abstract": "Consider $M_n$ the maximal position at generation $n$ of a supercritical branching random walk. A\\\"id\\\u0027ekon (2013) obtained and described the convergence in law, as time $n$ goes to infinity, of $M_n-m_n$, where $m_n$ is an explicit function. Equivalently, he identified the limit of $\\mathbb{P}(M_n \u003e m_n + x)$, for any $x \\in \\mathbb{R}$. More recently, Luo (2025) gave an asymptotic equivalent for the upper large deviation probability, that is $\\mathbb{P}(M_n \u003e m_n + xn)$, for $x \u003e 0$. In this work, we study an intermediate regime, called upper moderate deviation. We obtain, under close-to-optimal integrability conditions, an asymptotic equivalent for $\\mathbb{P}(M_n \u003e m_n + x_n)$, where $x_n$ is such that $x_n \\to \\infty$ and $x_n = O(\\sqrt{n})$. Our proof is based on a strategy due to Bramson, Ding, and Zeitouni (2016). As a byproduct, we obtain information about the typical behavior of particles contributing to such deviations. Finally, we apply our main result to show the convergence in law of the centered maximum of a two-speed branching random walk in the mean regime and describe its limit.",
"arxiv_id": "2601.08766",
"authors": [
"Louis Chataignier",
"Lianghui Luo"
],
"categories": [
"math.PR"
],
"license": "http://creativecommons.org/licenses/by/4.0/",
"title": "Upper moderate deviation probabilities for the maximum of a branching random walk",
"url": "https://arxiv.org/abs/2601.08766",
"version": "v1"
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