Phase synchronization between collective rhythms of fully locked oscillator groups

We study the phase synchronization between collective rhythms of fully locked oscillator groups. For weakly interacting groups of two oscillators with global sinusoidal coupling, we analytically derive the collective phase coupling function, which determines the dynamics of the collective phase difference between the groups. We demonstrate that the groups can exhibit anti-phase collective synchronization in spite of microscopic in-phase external coupling and vice versa.