  The concept of soliton complex in a nonlinear dispersive medium is proposed.
It is shown that strongly interacting identical topological solitons in the
medium can form bound soliton complexes which move without radiation. This
phenomenon is considered to be universal and applicable to various physical
systems. The soliton complex and its "excited" states are described
analytically and numerically as solutions of nonlinear dispersive equations
with the fourth and higher spatial or mixed derivatives. The dispersive
sine-Gordon, double and triple sine-Gordon, and piecewise-linear models are
studied in detail. Mechanisms and conditions of the formation of soliton
complexes, and peculiarities of their stationary dynamics are investigated. A
phenomenological approach to the description of the complexes and the
classification of all the possible complex states are proposed. Some examples
of physical systems, where the phenomenon can be experimentally observed, are
briefly discussed.
