Critical radius and supremum of random spherical harmonics

TL;DR

The paper establishes a uniform lower bound on the critical radius of high-dimensional spherical harmonic immersions, enabling explicit tail probability formulas for supremum deviations of random spherical harmonics.

Contribution

It proves a uniform lower bound on the critical radius for spherical harmonic immersions, with implications for analyzing the supremum behavior of random spherical harmonics.

Findings

Uniform lower bound on critical radius as degree n increases

Explicit tail probability formulas for supremum deviations

Connection between supremum tail probabilities and Euler characteristics

Abstract

We first consider {\it deterministic} immersions of the $d$-dimensional sphere into high dimensional Euclidean spaces, where the immersion is via spherical harmonics of level $n$. The main result of the article is the, a priori unexpected, fact that there is a uniform lower bound to the critical radius of the immersions as $n\to\infty$. This fact has immediate implications for {\it random} spherical harmonics with fixed $L^2$-norm. In particular, it leads to an exact and explicit formulae for the tail probability of their (large deviation) suprema by the tube formula, and also relates this to the expected Euler characteristic of their upper level sets.