Abstract

The Kuramoto model is a paradigm for studying oscillator networks with interplay between coupling tending towards synchronization, and heterogeneity in the oscillator population driving away from synchrony. In continuum versions of this model an oscillator population is represented by a probability density on the circle. Ott and Antonsen identified a special class of densities which is invariant under the dynamics and on which the dynamics are low-dimensional and analytically tractable. The reduction to the OA manifold has been used to analyze the dynamics of many variants of the Kuramoto model. To address the fundamental question of whether the OA manifold is attracting, we develop a systematic technique using weighted averages of Poisson measures for analyzing dynamics off the OA manifold. We show that for models with a finite number of populations, the OA manifold is {\it not} attracting in any sense; moreover, the dynamics off the OA manifold is often more complex than on the OA manifold, even at the level of macroscopic order parameters. The OA manifold consists of Poisson densities $\rho_\omega$. A simple extension of the OA manifold consists of averages of pairs of Poisson densities; then the hyperbolic distance between the centroids of each Poisson pair is a dynamical invariant (for each $\omega$). These conserved quantities, defined on the double Poisson manifold, are a measure of the distance to the OA manifold. This invariance implies that chimera states, which have some but not all populations in sync, can never be stable in the full state space, even if stable in the OA manifold. More broadly, our framework facilitates the analysis of multi-population continuum Kuramoto networks beyond the restrictions of the OA manifold, and has the potential to reveal more intricate dynamical behavior than has previously been observed for these networks.

Highlights

  • The Kuramoto oscillator model, first proposed by Kuramoto in 1975 [1], is the dynamical system governed by the equations θj = ωj + K NN sin(θk − θ j ), j = 1, . . . , N. (1) k=1Here, θ j is an angular variable, which we can think of as representing a point on the unit circle S1, so the state space for this system is the N-fold torus T N = (S1)N

  • Ott and Antonsen proved that this condition is preserved by the system dynamics, so the OA manifold XOA consisting of Poisson states f satisfying this additional condition is invariant. (Ott and Antonsen parametrized their Poisson densities by the conjugate of the centroid, so their analytic continuation was in the lower halfplane.) The analysis of the order parameter Z on XOA is facilitated by the analytic continuation condition; as shown in Ref. [5], if we integrate (16) over R against g(ω), we obtain

  • For the finite-N continuum Kuramoto model, the Poisson manifold is generally not attracting, and does not capture the complexity of the dynamics on the full state space. We demonstrated this by defining the larger double Poisson manifold and showed that one can assign a measure of the distance of a state to the Poisson manifold which is dynamically invariant

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Summary

INTRODUCTION

The Kuramoto oscillator model, first proposed by Kuramoto in 1975 [1], is the dynamical system governed by the equations θj. To drive home this point, we will show that the stable long-term dynamics off the OA manifold is usually qualitatively distinct and more complex than that on the OA manifold This has important ramifications for the study of finite population continuum Kuramoto models and especially the existence and stability of chimera states [7,8,9,10,11]. We give a similar construction of families of invariant manifolds off the OA manifold in the infinite-N continuum case, as well as a measure of the distance to the OA manifold The dynamics on these families are given explicitly. As in the finite-N case, the steady-state dynamics of the individual oscillator populations is typically more complex off the OA manifold. In our framework we can see this explicitly; using techniques from hyperbolic geometry, we prove that the macroscopic order parameter on our extended OA manifolds must have the same asymptotic dynamics as on the OA manifold

System setup
Poisson manifold XP
Multi-Poisson manifolds: dynamics of XP
Order parameter dynamics: an example
Multi-Poissons are dense
INFINITE-N CONTINUUM SYSTEM
Poisson and OA manifolds
Multi-Poisson and OA manifolds: dynamics off XP and XOA
Order parameter dynamics off XOA
CONCLUSION
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