On the optimal multilinear Bohnenblust--Hille constants

TL;DR

This paper improves upper bounds for the optimal constants in the multilinear Bohnenblust--Hille inequality for both real and complex scalars, providing sharper estimates for large n.

Contribution

It offers new, tighter upper bounds for the constants in the multilinear Bohnenblust--Hille inequality, enhancing previous estimates and extending results for higher n.

Findings

Improved bounds for real scalars: K_n ≤ √2(n-1)^0.526322

Improved bounds for complex scalars: K_n ≤ (2/√π)(n-1)^0.304975

Sharper estimates for large n, e.g., K_n < 1.30379(n-1)^0.526322 for real scalars when n > 256

Abstract

The upper estimates for the optimal constants of the multilinear Bohnenblust--Hille inequality obtained in [J. Funct. Anal. 264 (2013), 429--463] are here improved to: {0.1cm} {enumerate} For real scalars: $K_{n}\leq\sqrt{2}(n-1)^{0.526322}$. For complex scalars: $K_{n}\leq\frac{2}{\sqrt{\pi}}(n-1)^{0.304975}$.{enumerate} {0.1cm} \noindent We also obtain sharper estimates for higher values of $n$. For instance, \[ K_{n}<1.30379(n-1) ^{0.526322}\] for real scalars and $n>2^{8}$ and \[ K_{n}<0.99137(n-1) ^{0.304975}\] for complex scalars and $n > 2^{15}.$