Majorizing-measure bounds in the realized square-function metric
Abstract
The predictable square function measures the size of a martingale. Applied to parameter differences, it also defines a random pseudometric. We explain how to perform a majorizing-measure argument directly in this realized geometry, without conditioning the terminal field to be Gaussian and without first replacing the metric by a random multiple of a deterministic one. For a finite family of predictable Gaussian sums in a (2,D)-smooth Banach space, and a fixed probability measure μ on the parameter set, we prove normmaxjoscT fjLp ≤ CDnormGμ(d)+√p ΔdLp, p≥1, where Δd is the diameter of the parameter space in the terminal square-function metric and Gμ(d) is its ball-mass integral. The proof combines a localized exponential inequality, pathwise averaging over random balls, and a stopping-time argument. Atomic measures recover logarithmically weighted maximal inequalities; Haar measure connects the result with homogeneous entropy and continuity estimates. We also give extensions, examples, and a precise account of the restrictions on choosing the averaging measure.
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BibTeX
@misc{bednorz2026majorizingmeasure,
title = {{Majorizing-measure bounds in the realized square-function metric}},
author = {Witold M. Bednorz and Rafał M. Łochowski},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.38425},
eprint = {2609.38425},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.38425},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Majorizing-measure bounds in the realized square-function metric
AU - Witold M. Bednorz
AU - Rafał M. Łochowski
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.38425
UR - https://arxiv.org/abs/2609.38425
AB - The predictable square function measures the size of a martingale. Applied to parameter differences, it also defines a random pseudometric. We explain how to perform a majorizing-measure argument directly in this realized geometry, without conditioning the terminal field to be Gaussian and without first replacing the metric by a random multiple of a deterministic one. For a finite family of predictable Gaussian sums in a (2,D)-smooth Banach space, and a fixed probability measure μ on the parameter set, we prove normmax_josc_T f_j_L^p ≤ CDnormG_μ(d)+√p Δ_d_L^p, p≥1, where Δ_d is the diameter of the parameter space in the terminal square-function metric and G_μ(d) is its ball-mass integral. The proof combines a localized exponential inequality, pathwise averaging over random balls, and a stopping-time argument. Atomic measures recover logarithmically weighted maximal inequalities; Haar measure connects the result with homogeneous entropy and continuity estimates. We also give extensions, examples, and a precise account of the restrictions on choosing the averaging measure.
ER -