Extremals for Trudinger-Moser inequalities via polygonal profiles

Abstract

The aim of this paper is to establish the existence of extremal functions for the Trudinger--Moser inequality with logarithmic weights $(-\log |x|)^β$ in two dimensions throughout the full range $0\le β<1$. We also extend recent results on the existence of local maximizers for the Trudinger--Moser functional beyond the critical threshold. Our approach uses polygonal profiles to establish a lower bound uniform in the weight parameter. An explicit thirty-node profile gives the lower bound $\mathrm{TM}_{4π}>4.38421793217\,π$ for the classical critical supremum on the unit disk, improving on the value $4.3556\,π$ obtained in the computer experiments of Carleson and Chang. This lower bound has a purely analytic proof, which uses only elementary inequalities and exact rational arithmetic. Numerical experiments with polygonal profiles of up to $102400$ nodes suggest that this lower bound can be raised to $4.402732044\,π$, which improves the recent computational lower bound by Li and Sun.