Periodic Fisher-KPP equations on a regular tree

Abstract

We study Fisher-KPP equations on regular trees with reactions periodic in a Busemann coordinate or in distance from a vertex or a bi-infinite geodesic. For nonzero finitely supported data, we characterize the spectral threshold between uniform extinction and persistence, including critical extinction. We establish Bramson corrections for Busemann step data at positive, zero and negative speeds and, above the periodic extinction threshold, for the largest Busemann coordinate and radial level positions of finitely supported solutions. When the periodic spectral minimum is nonpositive but the geodesic spectral threshold is positive, we construct a smallest positive stationary solution with exponential transverse decay, prove uniqueness under an exponential bound, and determine longitudinal spreading with its logarithmic correction. We also classify positive stationary solutions depending only on distance from the geodesic and prove existence and stability results for moving and stationary fronts.