A height transportation approach to the quantitative Prékopa--Leindler inequality

Abstract

We give a new, simpler proof of sharp stability for the Prékopa--Leindler inequality. In contrast to the main arguments from Figalli, van Hintum and Tiba~\cite{FigalliVanHintumTibaPL}, our proof hinges mostly on the sharp stability theory for the Brunn--Minkowski problem, developed by the same authors \cite{figalli2024BM}, and on the idea of using a height transportation approach in order to match level sets. As a by-product of our techniques, we are able to prove the sharp dependency on $τ= \min\{λ,1-λ\}$ in the Prékopa--Leindler stability constant whenever one of the inputs is logarithmically concave, producing a new, simplified proof of two of the main results from~\cite{FigalliVanHintumTibaPL}. Finally, in the same fashion as Kristály and Pîrvuceanu \cite{kristaly2026quantitative}, we are able to obtain new stability results for the Bakry-Emery log-Sobolev inequality and for the Talagrand inequality. Due to the sharpness of the inputs, these results are optimal in terms of exponents. We moreover show that the $L^1$ nature of the distance in such results \emph{cannot} in general be improved to any other $L^p$ distance, where $p>1.$