Role Of The Internal Degree Of Freedom Of Particles In Cluster Formation

How the internal degree of freedom of particles influences self-organization is explored by considering cluster formation in many-particle systems. We analyze a general class of dynamical systems in which the interactions between particles depend on their spatial distance and the difference of their internal states. In particular, we analyze a three-particle system in which two types of steady patterns exist, namely, (i) a regular triangle (two-dimensional cluster) and (ii) a straight line (one-dimensional cluster). The results show that the linear pattern can be stable when the internal degree of freedom exists, while it is always unstable when the dynamics depend only on the spatial distance. Based on this analysis, we can understand why this difference occurs. If the internal states can cause asymmetry of the interactions, this can enable the particles to remain in a one-dimensional cluster.