Group-wave resonances in nonlinear dispersive media: The case of gravity water waves

The dynamics of coherent nonlinear wave groups is shown to be drastically different from the classical scenario of weakly nonlinear wave interactions. The coherent groups generate non-resonant (bound) waves which can be synchronized with other linear waves. By virtue of the revealed mechanism the groups may emit waves with similar or different lengths, which propagate in the same or opposite direction.