Oscillatory translational instabilities of spot patterns in the Schnakenberg system on general 2D domains

J. C. Tzou, S. Xie

Research output: Contribution to journalArticlepeer-review

Abstract

For a bounded 2D planar domain Ω, we investigate the impact of domain geometry on oscillatory translational instabilities of N-spot equilibrium solutions for a singularly perturbed Schnakenberg reaction-diffusion system with O(ε2) ≪ O(1) activator-inhibitor diffusivity ratio. An N-spot equilibrium is characterized by an activator concentration that is exponentially small everywhere in Ω except in N well-separated localized regions of O(ε) extent. We use the method of matched asymptotic analysis to analyze Hopf bifurcation thresholds above which the equilibrium becomes unstable to translational perturbations, which result in O(ε2) -frequency oscillations in the locations of the spots. We find that stability to these perturbations is governed by a nonlinear matrix-eigenvalue problem, the eigenvector of which is a 2N-vector that characterizes the possible modes (directions) of oscillation. The 2N × 2N matrix contains terms associated with a certain Green's function on Ω, which encodes geometric effects. For the special case of a perturbed disk with radius in polar coordinates r = 1 + σf(θ) with 0 < εσ ≪ 1, θ ∈ [0,2π), and f(θ) 2π-periodic, we show that only the mode-2 coefficients of the Fourier series of f impact the bifurcation threshold at leading order in σ. We further show that when f(θ) = cos2θ, the dominant mode of oscillation is in the direction parallel to the longer axis of the perturbed disk. Numerical investigations on the full Schnakenberg PDE are performed for various domains Ω and N-spot equilibria to confirm asymptotic results and also to demonstrate how domain geometry impacts thresholds and dominant oscillation modes.
Original languageEnglish
Pages (from-to)2473-2513
Number of pages41
JournalNonlinearity
Volume36
Issue number5
DOIs
Publication statusPublished - May 2023

Keywords

  • Hopf bifurcations
  • small eigenvalues
  • localized solutions
  • domain geometry

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