Logarithmic Bramson correction for multi-dimensional periodic Fisher-KPP equations

TL;DR

This paper analyzes the long-term behavior of solutions to multi-dimensional periodic Fisher-KPP equations, establishing a precise logarithmic correction (Bramson shift) in the propagation speed along different directions.

Contribution

It introduces a novel method to determine the Bramson shift in higher dimensions by linking propagation directions with minimizing directions, providing explicit asymptotic speeds.

Findings

Propagation speed includes a logarithmic correction term.

Unique correspondence between propagation directions and minimizing directions.

Asymptotic speed determined by a specific formula involving eigenvalues.

Abstract

We study the long time behavior of solutions of periodic Fisher-KPP type equations in $\mathbb{R}^n$ that arise from compactly supported initial data. We prove that propagation along a fixed direction $e\in\mathbb{S}^{n-1}$ is completely determined by an associated minimizing direction $e'$ which is unique and in a bijective correspondence with $e$. This correspondence allows us to determine the correct Bramson shift in higher dimensions and show that that the propagation along each $e$ occurs asymptotically at the speed $w_*(e)t-\frac{n/2+1}{\lambda_*(e')\,e\cdot e'}\log t+O(1)$.