Asymptotic estimates for unimodular multilinear forms with small norms on sequence spaces

TL;DR

This paper establishes asymptotic estimates for the minimal norms of unimodular multilinear forms on sequence spaces, revealing their behavior across various dimensions and p-norms, with implications for multilinear inequalities.

Contribution

It provides the first asymptotic estimates for the infimum norms of unimodular multilinear forms on sequence spaces for all p in [2, ∞], extending understanding in this area.

Findings

Asymptotic behavior of minimal norms characterized

Explicit formula involving dimensions and p-norms derived

Applications to multilinear Hardy--Littlewood inequality included

Abstract

The existence of unimodular forms with small norms on sequence spaces is crucial in a variety of problems in modern analysis. We prove that the infimum of $\left\Vert A\right\Vert $ over all unimodular $d$-linear (complex or real) forms $A$ on $\ell_{p_1}^{n_{1}} \times \cdots \times \ell_{p_d}^{n_{d}}$, for all $p_1,\dots,p_d \in [2, \infty]$ and all positive integers $n_1,\dots,n_d$, behaves (asymptotically) as $\left(n_{1}^{1/2} + \cdots + n_{d}^{1/2}\right) \prod_{j=1}^{d}n_{j}^{\frac{1}{2} - \frac{1}{p_j}}$. Applications to the theory of the multilinear Hardy--Littlewood inequality are also presented.