A tail-matching method for the linear stability of multi-vector-soliton bound states

Linear stability of multi-vector-soliton bound states in the coupled nonlinear Schr\"odinger equations is analyzed using a new tail-matching method. Under the condition that individual vector solitons in the bound states are wave-and-daughter-waves and widely separated, small eigenvalues of these bound states that bifurcate from the zero eigenvalue of single vector solitons are calculated explicitly. It is found that unstable eigenvalues from phase-mode bifurcations always exist, thus the bound states are always linearly unstable. This tail-matching method is simple, but it gives identical results as the Karpman-Solev'ev-Gorshkov-Ostrovsky method.