Low-amplitude breather and envelope solitons in quasi-one-dimensional physical models

In the low-amplitude limit we examine the breather- and envelope-soliton solutions of the generalized nonlinear Klein-Gordon system as nonlinear Schrödinger solitons. The existence of breather and envelope solutions is determined in the continuum and quasidiscrete limit; in this case the oscillations of the carrier in the envelope are treated exactly. The results are applied to the perturbed sine-Gordon and ${\phi }^4$ systems; in both cases the asymmetry of the breathers is controlled by the amplitude of the external force. The study is generalized to the calculations of low-amplitude breather modes in a ferromagnetic chain with a small out-of-plane angle.