An Elementary Proof of the Hanson-Wright Inequality

Fuente: arXiv
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Autore principale: Ziemann, Ingvar
Natura: Preprint
Pubblicazione: 2025
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author Ziemann, Ingvar
author_facet Ziemann, Ingvar
contents The Hanson-Wright inequality establishes exponential concentration for quadratic forms $X^T M X$, where $X$ is a vector with independent sub-Gaussian entries and with parameters depending on the Frobenius and operator norms of $M$. The most elementary proof to date is due to Rudelson & Vershinyn, who still rely on a convex decoupling argument due to Bourgain, followed by Gaussian comparison to arrive at the result. In this note we sidestep this decoupling and provide an arguably simpler proof reliant only on elementary properties of sub-Gaussian variables and Gaussian rotational invariance. As a consequence we also obtain improved constants.
format Preprint
id arxiv_https___arxiv_org_abs_2509_00881
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle An Elementary Proof of the Hanson-Wright Inequality
Ziemann, Ingvar
Probability
The Hanson-Wright inequality establishes exponential concentration for quadratic forms $X^T M X$, where $X$ is a vector with independent sub-Gaussian entries and with parameters depending on the Frobenius and operator norms of $M$. The most elementary proof to date is due to Rudelson & Vershinyn, who still rely on a convex decoupling argument due to Bourgain, followed by Gaussian comparison to arrive at the result. In this note we sidestep this decoupling and provide an arguably simpler proof reliant only on elementary properties of sub-Gaussian variables and Gaussian rotational invariance. As a consequence we also obtain improved constants.
title An Elementary Proof of the Hanson-Wright Inequality
topic Probability
url https://arxiv.org/abs/2509.00881